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FreeRTOS library
FreeRTOS is a library defining the following symbols:Most used functions
Name
Location
Summary
It is preferred that the macros xQueueSend(), xQueueSendToFront() and xQueueSendToBack() are used in place of calling this function directly. Post an item on a queue. The item is queued by copy, not by reference. This function must not be called from an interrupt service routine. See xQueueSendFromISR () for an alternative which may be used in an ISR. Example usage:
{c}
struct AMessage
{
char ucMessageID;
char ucData[ 20 ];
} xMessage;
uint32_t ulVar = 10UL;
void vATask( void *pvParameters )
{
QueueHandle_t xQueue1, xQueue2;
struct AMessage *pxMessage;
// Create a queue capable of containing 10 uint32_t values.
xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) );
// Create a queue capable of containing 10 pointers to AMessage structures.
// These should be passed by pointer as they contain a lot of data.
xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) );
// ...
if( xQueue1 != 0 )
{
// Send an uint32_t. Wait for 10 ticks for space to become
// available if necessary.
if( xQueueGenericSend( xQueue1, ( void * ) &ulVar, ( TickType_t ) 10, queueSEND_TO_BACK ) != pdPASS )
{
// Failed to post the message, even after 10 ticks.
}
}
if( xQueue2 != 0 )
{
// Send a pointer to a struct AMessage object. Don't block if the
// queue is already full.
pxMessage = & xMessage;
xQueueGenericSend( xQueue2, ( void * ) &pxMessage, ( TickType_t ) 0, queueSEND_TO_BACK );
}
// ... Rest of task code.
}
Delay a task for a given number of ticks. The actual time that the task remains blocked depends on the tick rate. The constant portTICK_PERIOD_MS can be used to calculate real time from the tick rate - with the resolution of one tick period. INCLUDE_vTaskDelay must be defined as 1 for this function to be available. See the configuration section for more information. vTaskDelay() specifies a time at which the task wishes to unblock relative to the time at which vTaskDelay() is called. For example, specifying a block period of 100 ticks will cause the task to unblock 100 ticks after vTaskDelay() is called. vTaskDelay() does not therefore provide a good method of controlling the frequency of a periodic task as the path taken through the code, as well as other task and interrupt activity, will affect the frequency at which vTaskDelay() gets called and therefore the time at which the task next executes. See xTaskDelayUntil() for an alternative API function designed to facilitate fixed frequency execution. It does this by specifying an absolute time (rather than a relative time) at which the calling task should unblock. Example usage:
{c}
void vTaskFunction( void * pvParameters )
{
// Block for 500ms.
const TickType_t xDelay = 500 / portTICK_PERIOD_MS;
for( ;; )
{
// Simply toggle the LED every 500ms, blocking between each toggle.
vToggleLED();
vTaskDelay( xDelay );
}
}
Exit a SMP critical section This function can be called in a nested manner. On the outer most level of nesting, this function will: - Release the spinlock - Restore the previous interrupt level before the critical section was entered If still nesting, this function simply decrements a critical nesting count
Enter a SMP critical section This function enters an SMP critical section by disabling interrupts then taking a spinlock with an unlimited timeout. This function can be called in a nested manner
INCLUDE_vTaskDelete must be defined as 1 for this function to be available. See the configuration section for more information. Remove a task from the RTOS real time kernel's management. The task being deleted will be removed from all ready, blocked, suspended and event lists. NOTE: The idle task is responsible for freeing the kernel allocated memory from tasks that have been deleted. It is therefore important that the idle task is not starved of microcontroller processing time if your application makes any calls to vTaskDelete (). Memory allocated by the task code is not automatically freed, and should be freed before the task is deleted. See the demo application file death.c for sample code that utilises vTaskDelete (). Example usage:
{c}
void vOtherFunction( void )
{
TaskHandle_t xHandle;
// Create the task, storing the handle.
xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, &xHandle );
// Use the handle to delete the task.
vTaskDelete( xHandle );
}
Get reentrancy structure of the current task - This function is required by newlib (when __DYNAMIC_REENT__ is enabled) - It will return a pointer to the current task's reent struct - If FreeRTOS is not running, it will return the global reent struct
Delete a queue - freeing all the memory allocated for storing of items placed on the queue.
Safe version of exit critical Safe version of enter critical will automatically select between portEXIT_CRITICAL() and portEXIT_CRITICAL_ISR()
Safe version of enter critical Safe version of enter critical will automatically select between portENTER_CRITICAL() and portENTER_CRITICAL_ISR()
Create a new task and add it to the list of tasks that are ready to run. Internally, within the FreeRTOS implementation, tasks use two blocks of memory. The first block is used to hold the task's data structures. The second block is used by the task as its stack. If a task is created using xTaskCreate() then both blocks of memory are automatically dynamically allocated inside the xTaskCreate() function. (see https://www.FreeRTOS.org/a00111.html). If a task is created using xTaskCreateStatic() then the application writer must provide the required memory. xTaskCreateStatic() therefore allows a task to be created without using any dynamic memory allocation. See xTaskCreateStatic() for a version that does not use any dynamic memory allocation. xTaskCreate() can only be used to create a task that has unrestricted access to the entire microcontroller memory map. Systems that include MPU support can alternatively create an MPU constrained task using xTaskCreateRestricted(). Example usage:
{c}
// Task to be created.
void vTaskCode( void * pvParameters )
{
for( ;; )
{
// Task code goes here.
}
}
// Function that creates a task.
void vOtherFunction( void )
{
static uint8_t ucParameterToPass;
TaskHandle_t xHandle = NULL;
// Create the task, storing the handle. Note that the passed parameter ucParameterToPass
// must exist for the lifetime of the task, so in this case is declared static. If it was just an
// an automatic stack variable it might no longer exist, or at least have been corrupted, by the time
// the new task attempts to access it.
xTaskCreate( vTaskCode, "NAME", STACK_SIZE, &ucParameterToPass, tskIDLE_PRIORITY, &xHandle );
configASSERT( xHandle );
// Use the handle to delete the task.
if( xHandle != NULL )
{
vTaskDelete( xHandle );
}
}
Receive an item from a queue. The item is received by copy so a buffer of adequate size must be provided. The number of bytes copied into the buffer was defined when the queue was created. Successfully received items are removed from the queue. This function must not be used in an interrupt service routine. See xQueueReceiveFromISR for an alternative that can. Example usage:
{c}
struct AMessage
{
char ucMessageID;
char ucData[ 20 ];
} xMessage;
QueueHandle_t xQueue;
// Task to create a queue and post a value.
void vATask( void *pvParameters )
{
struct AMessage *pxMessage;
// Create a queue capable of containing 10 pointers to AMessage structures.
// These should be passed by pointer as they contain a lot of data.
xQueue = xQueueCreate( 10, sizeof( struct AMessage * ) );
if( xQueue == 0 )
{
// Failed to create the queue.
}
// ...
// Send a pointer to a struct AMessage object. Don't block if the
// queue is already full.
pxMessage = & xMessage;
xQueueSend( xQueue, ( void * ) &pxMessage, ( TickType_t ) 0 );
// ... Rest of task code.
}
// Task to receive from the queue.
void vADifferentTask( void *pvParameters )
{
struct AMessage *pxRxedMessage;
if( xQueue != 0 )
{
// Receive a message on the created queue. Block for 10 ticks if a
// message is not immediately available.
if( xQueueReceive( xQueue, &( pxRxedMessage ), ( TickType_t ) 10 ) )
{
// pcRxedMessage now points to the struct AMessage variable posted
// by vATask.
}
}
// ... Rest of task code.
}
Set bits within an event group. This function cannot be called from an interrupt. xEventGroupSetBitsFromISR() is a version that can be called from an interrupt. Setting bits in an event group will automatically unblock tasks that are blocked waiting for the bits. Example usage:
{c}
#define BIT_0 ( 1 << 0 )
#define BIT_4 ( 1 << 4 )
void aFunction( EventGroupHandle_t xEventGroup )
{
EventBits_t uxBits;
// Set bit 0 and bit 4 in xEventGroup.
uxBits = xEventGroupSetBits(
xEventGroup, // The event group being updated.
BIT_0 | BIT_4 );// The bits being set.
if( ( uxBits & ( BIT_0 | BIT_4 ) ) == ( BIT_0 | BIT_4 ) )
{
// Both bit 0 and bit 4 remained set when the function returned.
}
else if( ( uxBits & BIT_0 ) != 0 )
{
// Bit 0 remained set when the function returned, but bit 4 was
// cleared. It might be that bit 4 was cleared automatically as a
// task that was waiting for bit 4 was removed from the Blocked
// state.
}
else if( ( uxBits & BIT_4 ) != 0 )
{
// Bit 4 remained set when the function returned, but bit 0 was
// cleared. It might be that bit 0 was cleared automatically as a
// task that was waiting for bit 0 was removed from the Blocked
// state.
}
else
{
// Neither bit 0 nor bit 4 remained set. It might be that a task
// was waiting for both of the bits to be set, and the bits were
// cleared as the task left the Blocked state.
}
}
Create a new task that is pinned to a particular core This function is similar to xTaskCreate(), but allows the creation of a pinned task. The task's pinned core is specified by the xCoreID argument. If xCoreID is set to tskNO_AFFINITY, then the task is unpinned and can run on any core.
Clear bits within an event group. This function cannot be called from an interrupt. Example usage:
{c}
#define BIT_0 ( 1 << 0 )
#define BIT_4 ( 1 << 4 )
void aFunction( EventGroupHandle_t xEventGroup )
{
EventBits_t uxBits;
// Clear bit 0 and bit 4 in xEventGroup.
uxBits = xEventGroupClearBits(
xEventGroup, // The event group being updated.
BIT_0 | BIT_4 );// The bits being cleared.
if( ( uxBits & ( BIT_0 | BIT_4 ) ) == ( BIT_0 | BIT_4 ) )
{
// Both bit 0 and bit 4 were set before xEventGroupClearBits() was
// called. Both will now be clear (not set).
}
else if( ( uxBits & BIT_0 ) != 0 )
{
// Bit 0 was set before xEventGroupClearBits() was called. It will
// now be clear.
}
else if( ( uxBits & BIT_4 ) != 0 )
{
// Bit 4 was set before xEventGroupClearBits() was called. It will
// now be clear.
}
else
{
// Neither bit 0 nor bit 4 were set in the first place.
}
}
[Potentially] block to wait for one or more bits to be set within a previously created event group. This function cannot be called from an interrupt. Example usage:
{c}
#define BIT_0 ( 1 << 0 )
#define BIT_4 ( 1 << 4 )
void aFunction( EventGroupHandle_t xEventGroup )
{
EventBits_t uxBits;
const TickType_t xTicksToWait = 100 / portTICK_PERIOD_MS;
// Wait a maximum of 100ms for either bit 0 or bit 4 to be set within
// the event group. Clear the bits before exiting.
uxBits = xEventGroupWaitBits(
xEventGroup, // The event group being tested.
BIT_0 | BIT_4, // The bits within the event group to wait for.
pdTRUE, // BIT_0 and BIT_4 should be cleared before returning.
pdFALSE, // Don't wait for both bits, either bit will do.
xTicksToWait ); // Wait a maximum of 100ms for either bit to be set.
if( ( uxBits & ( BIT_0 | BIT_4 ) ) == ( BIT_0 | BIT_4 ) )
{
// xEventGroupWaitBits() returned because both bits were set.
}
else if( ( uxBits & BIT_0 ) != 0 )
{
// xEventGroupWaitBits() returned because just BIT_0 was set.
}
else if( ( uxBits & BIT_4 ) != 0 )
{
// xEventGroupWaitBits() returned because just BIT_4 was set.
}
else
{
// xEventGroupWaitBits() returned because xTicksToWait ticks passed
// without either BIT_0 or BIT_4 becoming set.
}
}
Create a new event group. Internally, within the FreeRTOS implementation, event groups use a [small] block of memory, in which the event group's structure is stored. If an event groups is created using xEventGroupCreate() then the required memory is automatically dynamically allocated inside the xEventGroupCreate() function. (see https://www.FreeRTOS.org/a00111.html). If an event group is created using xEventGroupCreateStatic() then the application writer must instead provide the memory that will get used by the event group. xEventGroupCreateStatic() therefore allows an event group to be created without using any dynamic memory allocation. Although event groups are not related to ticks, for internal implementation reasons the number of bits available for use in an event group is dependent on the configUSE_16_BIT_TICKS setting in FreeRTOSConfig.h. If configUSE_16_BIT_TICKS is 1 then each event group contains 8 usable bits (bit 0 to bit 7). If configUSE_16_BIT_TICKS is set to 0 then each event group has 24 usable bits (bit 0 to bit 23). The EventBits_t type is used to store event bits within an event group. Example usage:
{c}
// Declare a variable to hold the created event group.
EventGroupHandle_t xCreatedEventGroup;
// Attempt to create the event group.
xCreatedEventGroup = xEventGroupCreate();
// Was the event group created successfully?
if( xCreatedEventGroup == NULL )
{
// The event group was not created because there was insufficient
// FreeRTOS heap available.
}
else
{
// The event group was created.
}
Delete an event group that was previously created by a call to xEventGroupCreate(). Tasks that are blocked on the event group will be unblocked and obtain 0 as the event group's value.
It is preferred that the macros xQueueSendFromISR(), xQueueSendToFrontFromISR() and xQueueSendToBackFromISR() be used in place of calling this function directly. xQueueGiveFromISR() is an equivalent for use by semaphores that don't actually copy any data. Post an item on a queue. It is safe to use this function from within an interrupt service routine. Items are queued by copy not reference so it is preferable to only queue small items, especially when called from an ISR. In most cases it would be preferable to store a pointer to the item being queued. Example usage for buffered IO (where the ISR can obtain more than one value per call):
{c}
void vBufferISR( void )
{
char cIn;
BaseType_t xHigherPriorityTaskWokenByPost;
// We have not woken a task at the start of the ISR.
xHigherPriorityTaskWokenByPost = pdFALSE;
// Loop until the buffer is empty.
do
{
// Obtain a byte from the buffer.
cIn = portINPUT_BYTE( RX_REGISTER_ADDRESS );
// Post each byte.
xQueueGenericSendFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWokenByPost, queueSEND_TO_BACK );
} while( portINPUT_BYTE( BUFFER_COUNT ) );
// Now the buffer is empty we can switch context if necessary. Note that the
// name of the yield function required is port specific.
if( xHigherPriorityTaskWokenByPost )
{
portYIELD_FROM_ISR();
}
}
INCLUDE_vTaskSuspend must be defined as 1 for this function to be available. See the configuration section for more information. Suspend any task. When suspended a task will never get any microcontroller processing time, no matter what its priority. Calls to vTaskSuspend are not accumulative - i.e. calling vTaskSuspend () twice on the same task still only requires one call to vTaskResume () to ready the suspended task. Example usage:
{c}
void vAFunction( void )
{
TaskHandle_t xHandle;
// Create a task, storing the handle.
xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, &xHandle );
// ...
// Use the handle to suspend the created task.
vTaskSuspend( xHandle );
// ...
// The created task will not run during this period, unless
// another task calls vTaskResume( xHandle ).
//...
// Suspend ourselves.
vTaskSuspend( NULL );
// We cannot get here unless another task calls vTaskResume
// with our handle as the parameter.
}
Resumes scheduler activity after it was suspended by a call to vTaskSuspendAll(). xTaskResumeAll() only resumes the scheduler. It does not unsuspend tasks that were previously suspended by a call to vTaskSuspend(). Example usage:
{c}
void vTask1( void * pvParameters )
{
for( ;; )
{
// Task code goes here.
// ...
// At some point the task wants to perform a long operation during
// which it does not want to get swapped out. It cannot use
// taskENTER_CRITICAL ()/taskEXIT_CRITICAL () as the length of the
// operation may cause interrupts to be missed - including the
// ticks.
// Prevent the real time kernel swapping out the task.
vTaskSuspendAll ();
// Perform the operation here. There is no need to use critical
// sections as we have all the microcontroller processing time.
// During this time interrupts will still operate and the real
// time kernel tick count will be maintained.
// ...
// The operation is complete. Restart the kernel. We want to force
// a context switch - but there is no point if resuming the scheduler
// caused a context switch already.
if( !xTaskResumeAll () )
{
taskYIELD ();
}
}
}
Checks if the current core is in an ISR context - ISR context consist of Low/Mid priority ISR, or time tick ISR - High priority ISRs aren't detected here, but they normally cannot call C code, so that should not be an issue anyway.
Waits for a direct to task notification on a particular index in the calling task's notification array in a manner similar to taking a counting semaphore. See https://www.FreeRTOS.org/RTOS-task-notifications.html for details. configUSE_TASK_NOTIFICATIONS must be undefined or defined as 1 for this function to be available. Each task has a private array of "notification values" (or 'notifications'), each of which is a 32-bit unsigned integer (uint32_t). The constant configTASK_NOTIFICATION_ARRAY_ENTRIES sets the number of indexes in the array, and (for backward compatibility) defaults to 1 if left undefined. Prior to FreeRTOS V10.4.0 there was only one notification value per task. Events can be sent to a task using an intermediary object. Examples of such objects are queues, semaphores, mutexes and event groups. Task notifications are a method of sending an event directly to a task without the need for such an intermediary object. A notification sent to a task can optionally perform an action, such as update, overwrite or increment one of the task's notification values. In that way task notifications can be used to send data to a task, or be used as light weight and fast binary or counting semaphores. ulTaskNotifyTakeIndexed() is intended for use when a task notification is used as a faster and lighter weight binary or counting semaphore alternative. Actual FreeRTOS semaphores are taken using the xSemaphoreTake() API function, the equivalent action that instead uses a task notification is ulTaskNotifyTakeIndexed(). When a task is using its notification value as a binary or counting semaphore other tasks should send notifications to it using the xTaskNotifyGiveIndexed() macro, or xTaskNotifyIndex() function with the eAction parameter set to eIncrement. ulTaskNotifyTakeIndexed() can either clear the task's notification value at the array index specified by the uxIndexToWaitOn parameter to zero on exit, in which case the notification value acts like a binary semaphore, or decrement the notification value on exit, in which case the notification value acts like a counting semaphore. A task can use ulTaskNotifyTakeIndexed() to [optionally] block to wait for a notification. The task does not consume any CPU time while it is in the Blocked state. Where as xTaskNotifyWaitIndexed() will return when a notification is pending, ulTaskNotifyTakeIndexed() will return when the task's notification value is not zero. **NOTE** Each notification within the array operates independently - a task can only block on one notification within the array at a time and will not be unblocked by a notification sent to any other array index. Backward compatibility information: Prior to FreeRTOS V10.4.0 each task had a single "notification value", and all task notification API functions operated on that value. Replacing the single notification value with an array of notification values necessitated a new set of API functions that could address specific notifications within the array. ulTaskNotifyTake() is the original API function, and remains backward compatible by always operating on the notification value at index 0 in the array. Calling ulTaskNotifyTake() is equivalent to calling ulTaskNotifyTakeIndexed() with the uxIndexToWaitOn parameter set to 0. @cond !DOC_EXCLUDE_HEADER_SECTION
@endcond Suspends the scheduler without disabling interrupts. Context switches will not occur while the scheduler is suspended. After calling vTaskSuspendAll () the calling task will continue to execute without risk of being swapped out until a call to xTaskResumeAll () has been made. API functions that have the potential to cause a context switch (for example, xTaskDelayUntil(), xQueueSend(), etc.) must not be called while the scheduler is suspended. Example usage:
{c}
void vTask1( void * pvParameters )
{
for( ;; )
{
// Task code goes here.
// ...
// At some point the task wants to perform a long operation during
// which it does not want to get swapped out. It cannot use
// taskENTER_CRITICAL ()/taskEXIT_CRITICAL () as the length of the
// operation may cause interrupts to be missed - including the
// ticks.
// Prevent the real time kernel swapping out the task.
vTaskSuspendAll ();
// Perform the operation here. There is no need to use critical
// sections as we have all the microcontroller processing time.
// During this time interrupts will still operate and the kernel
// tick count will be maintained.
// ...
// The operation is complete. Restart the kernel.
xTaskResumeAll ();
}
}
Queries a timer to see if it is active or dormant. A timer will be dormant if: 1) It has been created but not started, or 2) It is an expired one-shot timer that has not been restarted. Timers are created in the dormant state. The xTimerStart(), xTimerReset(), xTimerStartFromISR(), xTimerResetFromISR(), xTimerChangePeriod() and xTimerChangePeriodFromISR() API functions can all be used to transition a timer into the active state. Example usage: @verbatim // This function assumes xTimer has already been created. void vAFunction( TimerHandle_t xTimer ) { if( xTimerIsTimerActive( xTimer ) != pdFALSE ) // or more simply and equivalently "if( xTimerIsTimerActive( xTimer ) )" { // xTimer is active, do something. } else { // xTimer is not active, do something else. } } @endverbatim
Re-enable interrupts in a nested manner (meant to be called from ISRs) @warning Only applies to current CPU.
Receive an item from a queue. It is safe to use this function from within an interrupt service routine. Example usage:
{c}
QueueHandle_t xQueue;
// Function to create a queue and post some values.
void vAFunction( void *pvParameters )
{
char cValueToPost;
const TickType_t xTicksToWait = ( TickType_t )0xff;
// Create a queue capable of containing 10 characters.
xQueue = xQueueCreate( 10, sizeof( char ) );
if( xQueue == 0 )
{
// Failed to create the queue.
}
// ...
// Post some characters that will be used within an ISR. If the queue
// is full then this task will block for xTicksToWait ticks.
cValueToPost = 'a';
xQueueSend( xQueue, ( void * ) &cValueToPost, xTicksToWait );
cValueToPost = 'b';
xQueueSend( xQueue, ( void * ) &cValueToPost, xTicksToWait );
// ... keep posting characters ... this task may block when the queue
// becomes full.
cValueToPost = 'c';
xQueueSend( xQueue, ( void * ) &cValueToPost, xTicksToWait );
}
// ISR that outputs all the characters received on the queue.
void vISR_Routine( void )
{
BaseType_t xTaskWokenByReceive = pdFALSE;
char cRxedChar;
while( xQueueReceiveFromISR( xQueue, ( void * ) &cRxedChar, &xTaskWokenByReceive) )
{
// A character was received. Output the character now.
vOutputCharacter( cRxedChar );
// If removing the character from the queue woke the task that was
// posting onto the queue xTaskWokenByReceive will have been set to
// pdTRUE. No matter how many times this loop iterates only one
// task will be woken.
}
if( xTaskWokenByReceive != ( char ) pdFALSE;
{
taskYIELD ();
}
}
Creates a new software timer instance, and returns a handle by which the created software timer can be referenced. Internally, within the FreeRTOS implementation, software timers use a block of memory, in which the timer data structure is stored. If a software timer is created using xTimerCreate() then the required memory is automatically dynamically allocated inside the xTimerCreate() function. (see https://www.FreeRTOS.org/a00111.html). If a software timer is created using xTimerCreateStatic() then the application writer must provide the memory that will get used by the software timer. xTimerCreateStatic() therefore allows a software timer to be created without using any dynamic memory allocation. Timers are created in the dormant state. The xTimerStart(), xTimerReset(), xTimerStartFromISR(), xTimerResetFromISR(), xTimerChangePeriod() and xTimerChangePeriodFromISR() API functions can all be used to transition a timer into the active state. Example usage: @verbatim #define NUM_TIMERS 5 // An array to hold handles to the created timers. TimerHandle_t xTimers[ NUM_TIMERS ]; // An array to hold a count of the number of times each timer expires. int32_t lExpireCounters[ NUM_TIMERS ] = { 0 }; // Define a callback function that will be used by multiple timer instances. // The callback function does nothing but count the number of times the // associated timer expires, and stop the timer once the timer has expired // 10 times. void vTimerCallback( TimerHandle_t pxTimer ) { int32_t lArrayIndex; const int32_t xMaxExpiryCountBeforeStopping = 10; // Optionally do something if the pxTimer parameter is NULL. configASSERT( pxTimer ); // Which timer expired? lArrayIndex = ( int32_t ) pvTimerGetTimerID( pxTimer ); // Increment the number of times that pxTimer has expired. lExpireCounters[ lArrayIndex ] += 1; // If the timer has expired 10 times then stop it from running. if( lExpireCounters[ lArrayIndex ] == xMaxExpiryCountBeforeStopping ) { // Do not use a block time if calling a timer API function from a // timer callback function, as doing so could cause a deadlock! xTimerStop( pxTimer, 0 ); } } void main( void ) { int32_t x; // Create then start some timers. Starting the timers before the scheduler // has been started means the timers will start running immediately that // the scheduler starts. for( x = 0; x < NUM_TIMERS; x++ ) { xTimers[ x ] = xTimerCreate( "Timer", // Just a text name, not used by the kernel. ( 100 * ( x + 1 ) ), // The timer period in ticks. pdTRUE, // The timers will auto-reload themselves when they expire. ( void * ) x, // Assign each timer a unique id equal to its array index. vTimerCallback // Each timer calls the same callback when it expires. ); if( xTimers[ x ] == NULL ) { // The timer was not created. } else { // Start the timer. No block time is specified, and even if one was // it would be ignored because the scheduler has not yet been // started. if( xTimerStart( xTimers[ x ], 0 ) != pdPASS ) { // The timer could not be set into the Active state. } } } // ... // Create tasks here. // ... // Starting the scheduler will start the timers running as they have already // been set into the active state. vTaskStartScheduler(); // Should not reach here. for( ;; ); } @endverbatim
Disable interrupts in a nested manner (meant to be called from ISRs) @warning Only applies to current CPU.
See https://www.FreeRTOS.org/RTOS-task-notifications.html for details. configUSE_TASK_NOTIFICATIONS must be undefined or defined as 1 for these functions to be available. Sends a direct to task notification to a task, with an optional value and action. Each task has a private array of "notification values" (or 'notifications'), each of which is a 32-bit unsigned integer (uint32_t). The constant configTASK_NOTIFICATION_ARRAY_ENTRIES sets the number of indexes in the array, and (for backward compatibility) defaults to 1 if left undefined. Prior to FreeRTOS V10.4.0 there was only one notification value per task. Events can be sent to a task using an intermediary object. Examples of such objects are queues, semaphores, mutexes and event groups. Task notifications are a method of sending an event directly to a task without the need for such an intermediary object. A notification sent to a task can optionally perform an action, such as update, overwrite or increment one of the task's notification values. In that way task notifications can be used to send data to a task, or be used as light weight and fast binary or counting semaphores. A task can use xTaskNotifyWaitIndexed() or ulTaskNotifyTakeIndexed() to [optionally] block to wait for a notification to be pending. The task does not consume any CPU time while it is in the Blocked state. A notification sent to a task will remain pending until it is cleared by the task calling xTaskNotifyWaitIndexed() or ulTaskNotifyTakeIndexed() (or their un-indexed equivalents). If the task was already in the Blocked state to wait for a notification when the notification arrives then the task will automatically be removed from the Blocked state (unblocked) and the notification cleared. **NOTE** Each notification within the array operates independently - a task can only block on one notification within the array at a time and will not be unblocked by a notification sent to any other array index. Backward compatibility information: Prior to FreeRTOS V10.4.0 each task had a single "notification value", and all task notification API functions operated on that value. Replacing the single notification value with an array of notification values necessitated a new set of API functions that could address specific notifications within the array. xTaskNotify() is the original API function, and remains backward compatible by always operating on the notification value at index 0 in the array. Calling xTaskNotify() is equivalent to calling xTaskNotifyIndexed() with the uxIndexToNotify parameter set to 0. eSetBits - The target notification value is bitwise ORed with ulValue. xTaskNotifyIndexed() always returns pdPASS in this case. eIncrement - The target notification value is incremented. ulValue is not used and xTaskNotifyIndexed() always returns pdPASS in this case. eSetValueWithOverwrite - The target notification value is set to the value of ulValue, even if the task being notified had not yet processed the previous notification at the same array index (the task already had a notification pending at that index). xTaskNotifyIndexed() always returns pdPASS in this case. eSetValueWithoutOverwrite - If the task being notified did not already have a notification pending at the same array index then the target notification value is set to ulValue and xTaskNotifyIndexed() will return pdPASS. If the task being notified already had a notification pending at the same array index then no action is performed and pdFAIL is returned. eNoAction - The task receives a notification at the specified array index without the notification value at that index being updated. ulValue is not used and xTaskNotifyIndexed() always returns pdPASS in this case. pulPreviousNotificationValue - Can be used to pass out the subject task's notification value before any bits are modified by the notify function. @cond !DOC_EXCLUDE_HEADER_SECTION
Deletes a semaphore previously created using one of the xSemaphoreCreate...WithCaps() functions
Deletes a queue previously created using xQueueCreateWithCaps()
Determines if pxTicksToWait ticks has passed since a time was captured using a call to vTaskSetTimeOutState(). The captured time includes the tick count and the number of times the tick count has overflowed. @see https://www.FreeRTOS.org/xTaskCheckForTimeOut.html Example Usage:
{c}
// Driver library function used to receive uxWantedBytes from an Rx buffer
// that is filled by a UART interrupt. If there are not enough bytes in the
// Rx buffer then the task enters the Blocked state until it is notified that
// more data has been placed into the buffer. If there is still not enough
// data then the task re-enters the Blocked state, and xTaskCheckForTimeOut()
// is used to re-calculate the Block time to ensure the total amount of time
// spent in the Blocked state does not exceed MAX_TIME_TO_WAIT. This
// continues until either the buffer contains at least uxWantedBytes bytes,
// or the total amount of time spent in the Blocked state reaches
// MAX_TIME_TO_WAIT - at which point the task reads however many bytes are
// available up to a maximum of uxWantedBytes.
size_t xUART_Receive( uint8_t *pucBuffer, size_t uxWantedBytes )
{
size_t uxReceived = 0;
TickType_t xTicksToWait = MAX_TIME_TO_WAIT;
TimeOut_t xTimeOut;
// Initialize xTimeOut. This records the time at which this function
// was entered.
vTaskSetTimeOutState( &xTimeOut );
// Loop until the buffer contains the wanted number of bytes, or a
// timeout occurs.
while( UART_bytes_in_rx_buffer( pxUARTInstance ) < uxWantedBytes )
{
// The buffer didn't contain enough data so this task is going to
// enter the Blocked state. Adjusting xTicksToWait to account for
// any time that has been spent in the Blocked state within this
// function so far to ensure the total amount of time spent in the
// Blocked state does not exceed MAX_TIME_TO_WAIT.
if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) != pdFALSE )
{
//Timed out before the wanted number of bytes were available,
// exit the loop.
break;
}
// Wait for a maximum of xTicksToWait ticks to be notified that the
// receive interrupt has placed more data into the buffer.
ulTaskNotifyTake( pdTRUE, xTicksToWait );
}
// Attempt to read uxWantedBytes from the receive buffer into pucBuffer.
// The actual number of bytes read (which might be less than
// uxWantedBytes) is returned.
uxReceived = UART_read_from_receive_buffer( pxUARTInstance,
pucBuffer,
uxWantedBytes );
return uxReceived;
}
A version of xTaskNotifyGiveIndexed() that can be called from an interrupt service routine (ISR). See https://www.FreeRTOS.org/RTOS-task-notifications.html for more details. configUSE_TASK_NOTIFICATIONS must be undefined or defined as 1 for this macro to be available. Each task has a private array of "notification values" (or 'notifications'), each of which is a 32-bit unsigned integer (uint32_t). The constant configTASK_NOTIFICATION_ARRAY_ENTRIES sets the number of indexes in the array, and (for backward compatibility) defaults to 1 if left undefined. Prior to FreeRTOS V10.4.0 there was only one notification value per task. Events can be sent to a task using an intermediary object. Examples of such objects are queues, semaphores, mutexes and event groups. Task notifications are a method of sending an event directly to a task without the need for such an intermediary object. A notification sent to a task can optionally perform an action, such as update, overwrite or increment one of the task's notification values. In that way task notifications can be used to send data to a task, or be used as light weight and fast binary or counting semaphores. vTaskNotifyGiveIndexedFromISR() is intended for use when task notifications are used as light weight and faster binary or counting semaphore equivalents. Actual FreeRTOS semaphores are given from an ISR using the xSemaphoreGiveFromISR() API function, the equivalent action that instead uses a task notification is vTaskNotifyGiveIndexedFromISR(). When task notifications are being used as a binary or counting semaphore equivalent then the task being notified should wait for the notification using the ulTaskNotifyTakeIndexed() API function rather than the xTaskNotifyWaitIndexed() API function. **NOTE** Each notification within the array operates independently - a task can only block on one notification within the array at a time and will not be unblocked by a notification sent to any other array index. Backward compatibility information: Prior to FreeRTOS V10.4.0 each task had a single "notification value", and all task notification API functions operated on that value. Replacing the single notification value with an array of notification values necessitated a new set of API functions that could address specific notifications within the array. xTaskNotifyFromISR() is the original API function, and remains backward compatible by always operating on the notification value at index 0 within the array. Calling xTaskNotifyGiveFromISR() is equivalent to calling xTaskNotifyGiveIndexedFromISR() with the uxIndexToNotify parameter set to 0.
INCLUDE_uxTaskPriorityGet must be defined as 1 for this function to be available. See the configuration section for more information. Obtain the priority of any task. Example usage:
{c}
void vAFunction( void )
{
TaskHandle_t xHandle;
// Create a task, storing the handle.
xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, &xHandle );
// ...
// Use the handle to obtain the priority of the created task.
// It was created with tskIDLE_PRIORITY, but may have changed
// it itself.
if( uxTaskPriorityGet( xHandle ) != tskIDLE_PRIORITY )
{
// The task has changed it's priority.
}
// ...
// Is our priority higher than the created task?
if( uxTaskPriorityGet( xHandle ) < uxTaskPriorityGet( NULL ) )
{
// Our priority (obtained using NULL handle) is higher.
}
}
Sets the ID assigned to the timer. IDs are assigned to timers using the pvTimerID parameter of the call to xTimerCreated() that was used to create the timer. If the same callback function is assigned to multiple timers then the timer ID can be used as time specific (timer local) storage. Example usage: See the xTimerCreate() API function example usage scenario.
Utility function to check whether a yield (on either core) is required after unblocking (or changing the priority of) a particular task. - This function is the SMP replacement for checking if an unblocked task has a higher (or equal) priority than the current task. - It should be called before calling taskYIELD_IF_USING_PREEMPTION() or before setting xYieldRequired - If it is the other core that requires a yield, this function will internally trigger the other core to yield Note: In some special instances, a yield is triggered if the unblocked task has an equal priority (such as in xTaskResumeAll). Thus the xYieldEqualPriority parameter specifies whether to yield if the current task has equal priority. Scheduling Algorithm: This function will bias towards yielding the current core. - If the unblocked task has a higher (or equal) priority than the current core, the current core is yielded regardless of the current priority of the other core. - A core (current or other) will only yield if their schedulers are not suspended. Todo: This can be optimized (IDF-5772) Entry: - This function must be called in a critical section - A task must just have been unblocked, or its priority raised Exit: - Returns pdTRUE if the current core requires yielding - The other core will be triggered to yield if required
Create a new static task that is pinned to a particular core This function is similar to xTaskCreateStatic(), but allows the creation of a pinned task. The task's pinned core is specified by the xCoreID argument. If xCoreID is set to tskNO_AFFINITY, then the task is unpinned and can run on any core.
Creates a queue with specific memory capabilities This function is similar to xQueueCreate(), except that it allows the memory allocated for the queue to have specific capabilities (e.g., MALLOC_CAP_INTERNAL).
@endcond Creates a binary semaphore with specific memory capabilities This function is similar to vSemaphoreCreateBinary(), except that it allows the memory allocated for the binary semaphore to have specific capabilities (e.g., MALLOC_CAP_INTERNAL).
@endcond Waits for a direct to task notification to be pending at a given index within an array of direct to task notifications. See https://www.FreeRTOS.org/RTOS-task-notifications.html for details. configUSE_TASK_NOTIFICATIONS must be undefined or defined as 1 for this function to be available. Each task has a private array of "notification values" (or 'notifications'), each of which is a 32-bit unsigned integer (uint32_t). The constant configTASK_NOTIFICATION_ARRAY_ENTRIES sets the number of indexes in the array, and (for backward compatibility) defaults to 1 if left undefined. Prior to FreeRTOS V10.4.0 there was only one notification value per task. Events can be sent to a task using an intermediary object. Examples of such objects are queues, semaphores, mutexes and event groups. Task notifications are a method of sending an event directly to a task without the need for such an intermediary object. A notification sent to a task can optionally perform an action, such as update, overwrite or increment one of the task's notification values. In that way task notifications can be used to send data to a task, or be used as light weight and fast binary or counting semaphores. A notification sent to a task will remain pending until it is cleared by the task calling xTaskNotifyWaitIndexed() or ulTaskNotifyTakeIndexed() (or their un-indexed equivalents). If the task was already in the Blocked state to wait for a notification when the notification arrives then the task will automatically be removed from the Blocked state (unblocked) and the notification cleared. A task can use xTaskNotifyWaitIndexed() to [optionally] block to wait for a notification to be pending, or ulTaskNotifyTakeIndexed() to [optionally] block to wait for a notification value to have a non-zero value. The task does not consume any CPU time while it is in the Blocked state. **NOTE** Each notification within the array operates independently - a task can only block on one notification within the array at a time and will not be unblocked by a notification sent to any other array index. Backward compatibility information: Prior to FreeRTOS V10.4.0 each task had a single "notification value", and all task notification API functions operated on that value. Replacing the single notification value with an array of notification values necessitated a new set of API functions that could address specific notifications within the array. xTaskNotifyWait() is the original API function, and remains backward compatible by always operating on the notification value at index 0 in the array. Calling xTaskNotifyWait() is equivalent to calling xTaskNotifyWaitIndexed() with the uxIndexToWaitOn parameter set to 0.
Return the number of free spaces available in a queue. This is equal to the number of items that can be sent to the queue before the queue becomes full if no items are removed.
INCLUDE_vTaskSuspend must be defined as 1 for this function to be available. See the configuration section for more information. Resumes a suspended task. A task that has been suspended by one or more calls to vTaskSuspend () will be made available for running again by a single call to vTaskResume (). Example usage:
{c}
void vAFunction( void )
{
TaskHandle_t xHandle;
// Create a task, storing the handle.
xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, &xHandle );
// ...
// Use the handle to suspend the created task.
vTaskSuspend( xHandle );
// ...
// The created task will not run during this period, unless
// another task calls vTaskResume( xHandle ).
//...
// Resume the suspended task ourselves.
vTaskResume( xHandle );
// The created task will once again get microcontroller processing
// time in accordance with its priority within the system.
}
Checks if the current core can yield - A core cannot yield if its in an ISR or in a critical section
INCLUDE_uxTaskGetStackHighWaterMark must be set to 1 in FreeRTOSConfig.h for this function to be available. Returns the high water mark of the stack associated with xTask. That is, the minimum free stack space there has been (in words, so on a 32 bit machine a value of 1 means 4 bytes) since the task started. The smaller the returned number the closer the task has come to overflowing its stack. uxTaskGetStackHighWaterMark() and uxTaskGetStackHighWaterMark2() are the same except for their return type. Using configSTACK_DEPTH_TYPE allows the user to determine the return type. It gets around the problem of the value overflowing on 8-bit types without breaking backward compatibility for applications that expect an 8-bit return type.
INCLUDE_eTaskGetState must be defined as 1 for this function to be available. See the configuration section for more information. Obtain the state of any task. States are encoded by the eTaskState enumerated type.
See https://www.FreeRTOS.org/RTOS-task-notifications.html for details. configUSE_TASK_NOTIFICATIONS must be undefined or defined as 1 for these functions to be available. A version of xTaskNotifyIndexed() that can be used from an interrupt service routine (ISR). Each task has a private array of "notification values" (or 'notifications'), each of which is a 32-bit unsigned integer (uint32_t). The constant configTASK_NOTIFICATION_ARRAY_ENTRIES sets the number of indexes in the array, and (for backward compatibility) defaults to 1 if left undefined. Prior to FreeRTOS V10.4.0 there was only one notification value per task. Events can be sent to a task using an intermediary object. Examples of such objects are queues, semaphores, mutexes and event groups. Task notifications are a method of sending an event directly to a task without the need for such an intermediary object. A notification sent to a task can optionally perform an action, such as update, overwrite or increment one of the task's notification values. In that way task notifications can be used to send data to a task, or be used as light weight and fast binary or counting semaphores. A task can use xTaskNotifyWaitIndexed() to [optionally] block to wait for a notification to be pending, or ulTaskNotifyTakeIndexed() to [optionally] block to wait for a notification value to have a non-zero value. The task does not consume any CPU time while it is in the Blocked state. A notification sent to a task will remain pending until it is cleared by the task calling xTaskNotifyWaitIndexed() or ulTaskNotifyTakeIndexed() (or their un-indexed equivalents). If the task was already in the Blocked state to wait for a notification when the notification arrives then the task will automatically be removed from the Blocked state (unblocked) and the notification cleared. **NOTE** Each notification within the array operates independently - a task can only block on one notification within the array at a time and will not be unblocked by a notification sent to any other array index. Backward compatibility information: Prior to FreeRTOS V10.4.0 each task had a single "notification value", and all task notification API functions operated on that value. Replacing the single notification value with an array of notification values necessitated a new set of API functions that could address specific notifications within the array. xTaskNotifyFromISR() is the original API function, and remains backward compatible by always operating on the notification value at index 0 within the array. Calling xTaskNotifyFromISR() is equivalent to calling xTaskNotifyIndexedFromISR() with the uxIndexToNotify parameter set to 0. eSetBits - The task's notification value is bitwise ORed with ulValue. xTaskNotify() always returns pdPASS in this case. eIncrement - The task's notification value is incremented. ulValue is not used and xTaskNotify() always returns pdPASS in this case. eSetValueWithOverwrite - The task's notification value is set to the value of ulValue, even if the task being notified had not yet processed the previous notification (the task already had a notification pending). xTaskNotify() always returns pdPASS in this case. eSetValueWithoutOverwrite - If the task being notified did not already have a notification pending then the task's notification value is set to ulValue and xTaskNotify() will return pdPASS. If the task being notified already had a notification pending then no action is performed and pdFAIL is returned. eNoAction - The task receives a notification without its notification value being updated. ulValue is not used and xTaskNotify() always returns pdPASS in this case. @cond !DOC_EXCLUDE_HEADER_SECTION
Returns the ID assigned to the timer. IDs are assigned to timers using the pvTimerID parameter of the call to xTimerCreated() that was used to create the timer, and by calling the vTimerSetTimerID() API function. If the same callback function is assigned to multiple timers then the timer ID can be used as time specific (timer local) storage. Example usage: See the xTimerCreate() API function example usage scenario.
Queries a queue to determine if the queue is full. This function should only be used in an ISR.
Utility function to check whether a task can currently be scheduled on one or more cores. This function is the SMP replacement for checking if `uxSchedulerSuspended == 0`. - If a task is pinned, check the scheduler suspension state on the task's pinned core. The task can be scheduled if the scheduler is not suspended on the pinned core. - If a task is unpinned, check the scheduler suspension state on both cores. The task can be scheduled if the scheduler is not suspended on either of the cores.
Enter a SMP critical section with a timeout This function enters an SMP critical section by disabling interrupts then taking a spinlock with a specified timeout. This function can be called in a nested manner.
Get the current core ID of a particular task Helper function to get the core ID of a particular task. If the task is pinned to a particular core, the core ID is returned. If the task is not pinned to a particular core, tskNO_AFFINITY is returned. If CONFIG_FREERTOS_UNICORE is enabled, this function simply returns 0. [refactor-todo] See if this needs to be deprecated (IDF-8145)(IDF-8164)
Yields the other core - Send an interrupt to another core in order to make the task running on it yield for a higher-priority task. - Can be used to yield current core as well
Queries a stream buffer to see how much free space it contains, which is equal to the amount of data that can be sent to the stream buffer before it is full.
Get the handle of idle task for the given core. [refactor-todo] See if this needs to be deprecated (IDF-8145)
configUSE_TRACE_FACILITY must be defined as 1 in FreeRTOSConfig.h for uxTaskGetSystemState() to be available. uxTaskGetSystemState() populates an TaskStatus_t structure for each task in the system. TaskStatus_t structures contain, among other things, members for the task handle, task name, task priority, task state, and total amount of run time consumed by the task. See the TaskStatus_t structure definition in this file for the full member list. NOTE: This function is intended for debugging use only as its use results in the scheduler remaining suspended for an extended period. Example usage:
{c}
// This example demonstrates how a human readable table of run time stats
// information is generated from raw data provided by uxTaskGetSystemState().
// The human readable table is written to pcWriteBuffer
void vTaskGetRunTimeStats( char *pcWriteBuffer )
{
TaskStatus_t *pxTaskStatusArray;
volatile UBaseType_t uxArraySize, x;
configRUN_TIME_COUNTER_TYPE ulTotalRunTime, ulStatsAsPercentage;
// Make sure the write buffer does not contain a string.
pcWriteBuffer = 0x00;
// Take a snapshot of the number of tasks in case it changes while this
// function is executing.
uxArraySize = uxTaskGetNumberOfTasks();
// Allocate a TaskStatus_t structure for each task. An array could be
// allocated statically at compile time.
pxTaskStatusArray = pvPortMalloc( uxArraySize * sizeof( TaskStatus_t ) );
if( pxTaskStatusArray != NULL )
{
// Generate raw status information about each task.
uxArraySize = uxTaskGetSystemState( pxTaskStatusArray, uxArraySize, &ulTotalRunTime );
// For percentage calculations.
ulTotalRunTime /= 100UL;
// Avoid divide by zero errors.
if( ulTotalRunTime > 0 )
{
// For each populated position in the pxTaskStatusArray array,
// format the raw data as human readable ASCII data
for( x = 0; x < uxArraySize; x++ )
{
// What percentage of the total run time has the task used?
// This will always be rounded down to the nearest integer.
// ulTotalRunTimeDiv100 has already been divided by 100.
ulStatsAsPercentage = pxTaskStatusArray[ x ].ulRunTimeCounter / ulTotalRunTime;
if( ulStatsAsPercentage > 0UL )
{
sprintf( pcWriteBuffer, "%s\t\t%lu\t\t%lu%%\r\n", pxTaskStatusArray[ x ].pcTaskName, pxTaskStatusArray[ x ].ulRunTimeCounter, ulStatsAsPercentage );
}
else
{
// If the percentage is zero here then the task has
// consumed less than 1% of the total run time.
sprintf( pcWriteBuffer, "%s\t\t%lu\t\t<1%%\r\n", pxTaskStatusArray[ x ].pcTaskName, pxTaskStatusArray[ x ].ulRunTimeCounter );
}
pcWriteBuffer += strlen( ( char * ) pcWriteBuffer );
}
}
// The array is no longer needed, free the memory it consumes.
vPortFree( pxTaskStatusArray );
}
}
Get the handle of the task currently running on a certain core Because of the nature of SMP processing, there is no guarantee that this value will still be valid on return and should only be used for debugging purposes. [refactor-todo] See if this needs to be deprecated (IDF-8145)
Capture the current time for future use with xTaskCheckForTimeOut().
INCLUDE_vTaskPrioritySet must be defined as 1 for this function to be available. See the configuration section for more information. Set the priority of any task. A context switch will occur before the function returns if the priority being set is higher than the currently executing task. Example usage:
{c}
void vAFunction( void )
{
TaskHandle_t xHandle;
// Create a task, storing the handle.
xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, &xHandle );
// ...
// Use the handle to raise the priority of the created task.
vTaskPrioritySet( xHandle, tskIDLE_PRIORITY + 1 );
// ...
// Use a NULL handle to raise our priority to the same value.
vTaskPrioritySet( NULL, tskIDLE_PRIORITY + 1 );
}
Checks if a given piece of memory can be used to store a task's TCB - Defined in heap_idf.c
Used from application interrupt service routines to defer the execution of a function to the RTOS daemon task (the timer service task, hence this function is implemented in timers.c and is prefixed with 'Timer'). Ideally an interrupt service routine (ISR) is kept as short as possible, but sometimes an ISR either has a lot of processing to do, or needs to perform processing that is not deterministic. In these cases xTimerPendFunctionCallFromISR() can be used to defer processing of a function to the RTOS daemon task. A mechanism is provided that allows the interrupt to return directly to the task that will subsequently execute the pended callback function. This allows the callback function to execute contiguously in time with the interrupt - just as if the callback had executed in the interrupt itself. Example usage: @verbatim // The callback function that will execute in the context of the daemon task. // Note callback functions must all use this same prototype. void vProcessInterface( void *pvParameter1, uint32_t ulParameter2 ) { BaseType_t xInterfaceToService; // The interface that requires servicing is passed in the second // parameter. The first parameter is not used in this case. xInterfaceToService = ( BaseType_t ) ulParameter2; // ...Perform the processing here... } // An ISR that receives data packets from multiple interfaces void vAnISR( void ) { BaseType_t xInterfaceToService, xHigherPriorityTaskWoken; // Query the hardware to determine which interface needs processing. xInterfaceToService = prvCheckInterfaces(); // The actual processing is to be deferred to a task. Request the // vProcessInterface() callback function is executed, passing in the // number of the interface that needs processing. The interface to // service is passed in the second parameter. The first parameter is // not used in this case. xHigherPriorityTaskWoken = pdFALSE; xTimerPendFunctionCallFromISR( vProcessInterface, NULL, ( uint32_t ) xInterfaceToService, &xHigherPriorityTaskWoken ); // If xHigherPriorityTaskWoken is now set to pdTRUE then a context // switch should be requested. The macro used is port specific and will // be either portYIELD_FROM_ISR() or portEND_SWITCHING_ISR() - refer to // the documentation page for the port being used. portYIELD_FROM_ISR( xHigherPriorityTaskWoken ); } @endverbatim
This is a version of xTaskGetTickCount() that is safe to be called from an ISR - provided that TickType_t is the natural word size of the microcontroller being used or interrupt nesting is either not supported or not being used.
Creates a mutex semaphore with specific memory capabilities This function is similar to xSemaphoreCreateMutex(), except that it allows the memory allocated for the mutex semaphore to have specific capabilities (e.g., MALLOC_CAP_INTERNAL).
Checks if a given piece of memory can be used to store a FreeRTOS list - Defined in heap_idf.c
See https://www.FreeRTOS.org/RTOS-task-notifications.html for details. configUSE_TASK_NOTIFICATIONS must be undefined or defined as 1 for these functions to be available. Each task has a private array of "notification values" (or 'notifications'), each of which is a 32-bit unsigned integer (uint32_t). The constant configTASK_NOTIFICATION_ARRAY_ENTRIES sets the number of indexes in the array, and (for backward compatibility) defaults to 1 if left undefined. Prior to FreeRTOS V10.4.0 there was only one notification value per task. If a notification is sent to an index within the array of notifications then the notification at that index is said to be 'pending' until it is read or explicitly cleared by the receiving task. xTaskNotifyStateClearIndexed() is the function that clears a pending notification without reading the notification value. The notification value at the same array index is not altered. Set xTask to NULL to clear the notification state of the calling task. Backward compatibility information: Prior to FreeRTOS V10.4.0 each task had a single "notification value", and all task notification API functions operated on that value. Replacing the single notification value with an array of notification values necessitated a new set of API functions that could address specific notifications within the array. xTaskNotifyStateClear() is the original API function, and remains backward compatible by always operating on the notification value at index 0 within the array. Calling xTaskNotifyStateClear() is equivalent to calling xTaskNotifyStateClearIndexed() with the uxIndexToNotify parameter set to 0.
xTaskGetIdleTaskHandle() is only available if INCLUDE_xTaskGetIdleTaskHandle is set to 1 in FreeRTOSConfig.h. Simply returns the handle of the idle task of the current core. It is not valid to call xTaskGetIdleTaskHandle() before the scheduler has been started.
Retrieve pointers to a statically created stream buffer's data structure buffer and storage area buffer. These are the same buffers that are supplied at the time of creation.
@endcond This function is used to provide a statically allocated block of memory to FreeRTOS to hold the Timer Task TCB. This function is required when configSUPPORT_STATIC_ALLOCATION is set. For more information see this URI: https://www.FreeRTOS.org/a00110.html#configSUPPORT_STATIC_ALLOCATION
Utility task that simply returns pdTRUE if the task referenced by xTask is currently in the Suspended state, or pdFALSE if the task referenced by xTask is in any other state.
Creates a pinned task where its stack has specific memory capabilities This function is similar to xTaskCreatePinnedToCore(), except that it allows the memory allocated for the task's stack to have specific capabilities (e.g., MALLOC_CAP_SPIRAM). However, the specified capabilities will NOT apply to the task's TCB as a TCB must always be in internal RAM.
Get the next task using the task iterator. This function retrieves the next task in the traversal sequence.
Fill a TaskSnapshot_t structure for specified task. - This function is used by the panic handler to get the snapshot of a particular task.
INCLUDE_xTaskDelayUntil must be defined as 1 for this function to be available. See the configuration section for more information. Delay a task until a specified time. This function can be used by periodic tasks to ensure a constant execution frequency. This function differs from vTaskDelay () in one important aspect: vTaskDelay () will cause a task to block for the specified number of ticks from the time vTaskDelay () is called. It is therefore difficult to use vTaskDelay () by itself to generate a fixed execution frequency as the time between a task starting to execute and that task calling vTaskDelay () may not be fixed [the task may take a different path though the code between calls, or may get interrupted or preempted a different number of times each time it executes]. Whereas vTaskDelay () specifies a wake time relative to the time at which the function is called, xTaskDelayUntil () specifies the absolute (exact) time at which it wishes to unblock. The macro pdMS_TO_TICKS() can be used to calculate the number of ticks from a time specified in milliseconds with a resolution of one tick period. Example usage:
{c}
// Perform an action every 10 ticks.
void vTaskFunction( void * pvParameters )
{
TickType_t xLastWakeTime;
const TickType_t xFrequency = 10;
BaseType_t xWasDelayed;
// Initialise the xLastWakeTime variable with the current time.
xLastWakeTime = xTaskGetTickCount ();
for( ;; )
{
// Wait for the next cycle.
xWasDelayed = xTaskDelayUntil( &xLastWakeTime, xFrequency );
// Perform action here. xWasDelayed value can be used to determine
// whether a deadline was missed if the code here took too long.
}
}
Queries a queue to determine if the queue is empty. This function should only be used in an ISR.
Set local storage pointer and deletion callback. Each task contains an array of pointers that is dimensioned by the configNUM_THREAD_LOCAL_STORAGE_POINTERS setting in FreeRTOSConfig.h. The kernel does not use the pointers itself, so the application writer can use the pointers for any purpose they wish. Local storage pointers set for a task can reference dynamically allocated resources. This function is similar to vTaskSetThreadLocalStoragePointer, but provides a way to release these resources when the task gets deleted. For each pointer, a callback function can be set. This function will be called when task is deleted, with the local storage pointer index and value as arguments.
Fill an array of TaskSnapshot_t structures for every task in the system - This function is used by the panic handler to get a snapshot of all tasks in the system
configUSE_TRACE_FACILITY and configUSE_STATS_FORMATTING_FUNCTIONS must both be defined as 1 for this function to be available. See the configuration section of the FreeRTOS.org website for more information. NOTE 1: This function will disable interrupts for its duration. It is not intended for normal application runtime use but as a debug aid. Lists all the current tasks, along with their current state and stack usage high water mark. Tasks are reported as blocked ('B'), ready ('R'), deleted ('D') or suspended ('S'). PLEASE NOTE: This function is provided for convenience only, and is used by many of the demo applications. Do not consider it to be part of the scheduler. vTaskList() calls uxTaskGetSystemState(), then formats part of the uxTaskGetSystemState() output into a human readable table that displays task: names, states, priority, stack usage and task number. Stack usage specified as the number of unused StackType_t words stack can hold on top of stack - not the number of bytes. vTaskList() has a dependency on the sprintf() C library function that might bloat the code size, use a lot of stack, and provide different results on different platforms. An alternative, tiny, third party, and limited functionality implementation of sprintf() is provided in many of the FreeRTOS/Demo sub-directories in a file called printf-stdarg.c (note printf-stdarg.c does not provide a full snprintf() implementation!). It is recommended that production systems call uxTaskGetSystemState() directly to get access to raw stats data, rather than indirectly through a call to vTaskList().
@cond !DOC_EXCLUDE_HEADER_SECTION Starts the real time kernel tick processing. After calling the kernel has control over which tasks are executed and when. See the demo application file main.c for an example of creating tasks and starting the kernel. Example usage:
{c}
void vAFunction( void )
{
// Create at least one task before starting the kernel.
xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, NULL );
// Start the real time kernel with preemption.
vTaskStartScheduler ();
// Will not get here unless a task calls vTaskEndScheduler ()
}
Safe version of enter critical timeout Safe version of enter critical will automatically select between portTRY_ENTER_CRITICAL() and portTRY_ENTER_CRITICAL_ISR()
FreeRTOS Compliant version of xPortEnterCriticalTimeout() Compliant version of xPortEnterCriticalTimeout() will ensure that this is called from a task context only. An abort is called otherwise.
TCB cleanup hook The portCLEAN_UP_TCB() macro is called in prvDeleteTCB() right before a deleted task's memory is freed. We map that macro to this internal function so that IDF FreeRTOS ports can inject some task pre-deletion operations.
Checks if a given piece of memory can be used to store a task's stack - Defined in heap_idf.c
configUSE_TRACE_FACILITY must be defined as 1 for this function to be available. See the configuration section for more information. Populates a TaskStatus_t structure with information about a task. Example usage:
{c}
void vAFunction( void )
{
TaskHandle_t xHandle;
TaskStatus_t xTaskDetails;
// Obtain the handle of a task from its name.
xHandle = xTaskGetHandle( "Task_Name" );
// Check the handle is not NULL.
configASSERT( xHandle );
// Use the handle to obtain further information about the task.
vTaskGetInfo( xHandle,
&xTaskDetails,
pdTRUE, // Include the high water mark in xTaskDetails.
eInvalid ); // Include the task state in xTaskDetails.
}
Retrieve pointers to a statically created task's data structure buffer and stack buffer. These are the same buffers that are supplied at the time of creation.
The application stack overflow hook is called when a stack overflow is detected for a task. Details on stack overflow detection can be found here: https://www.FreeRTOS.org/Stacks-and-stack-overflow-checking.html
This function is used to provide a statically allocated block of memory to FreeRTOS to hold the Idle Task TCB. This function is required when configSUPPORT_STATIC_ALLOCATION is set. For more information see this URI: https://www.FreeRTOS.org/a00110.html#configSUPPORT_STATIC_ALLOCATION
Receive an item from a queue without removing the item from the queue. The item is received by copy so a buffer of adequate size must be provided. The number of bytes copied into the buffer was defined when the queue was created. Successfully received items remain on the queue so will be returned again by the next call, or a call to xQueueReceive(). This macro must not be used in an interrupt service routine. See xQueuePeekFromISR() for an alternative that can be called from an interrupt service routine. Example usage:
{c}
struct AMessage
{
char ucMessageID;
char ucData[ 20 ];
} xMessage;
QueueHandle_t xQueue;
// Task to create a queue and post a value.
void vATask( void *pvParameters )
{
struct AMessage *pxMessage;
// Create a queue capable of containing 10 pointers to AMessage structures.
// These should be passed by pointer as they contain a lot of data.
xQueue = xQueueCreate( 10, sizeof( struct AMessage * ) );
if( xQueue == 0 )
{
// Failed to create the queue.
}
// ...
// Send a pointer to a struct AMessage object. Don't block if the
// queue is already full.
pxMessage = & xMessage;
xQueueSend( xQueue, ( void * ) &pxMessage, ( TickType_t ) 0 );
// ... Rest of task code.
}
// Task to peek the data from the queue.
void vADifferentTask( void *pvParameters )
{
struct AMessage *pxRxedMessage;
if( xQueue != 0 )
{
// Peek a message on the created queue. Block for 10 ticks if a
// message is not immediately available.
if( xQueuePeek( xQueue, &( pxRxedMessage ), ( TickType_t ) 10 ) )
{
// pcRxedMessage now points to the struct AMessage variable posted
// by vATask, but the item still remains on the queue.
}
}
// ... Rest of task code.
}
Deletes a stream buffer that was previously created using a call to xStreamBufferCreate() or xStreamBufferCreateStatic(). If the stream buffer was created using dynamic memory (that is, by xStreamBufferCreate()), then the allocated memory is freed. A stream buffer handle must not be used after the stream buffer has been deleted.
Queries a timer to determine if it is an auto-reload timer, in which case the timer automatically resets itself each time it expires, or a one-shot timer, in which case the timer will only expire once unless it is manually restarted.
Create a new event group. Internally, within the FreeRTOS implementation, event groups use a [small] block of memory, in which the event group's structure is stored. If an event groups is created using xEventGroupCreate() then the required memory is automatically dynamically allocated inside the xEventGroupCreate() function. (see https://www.FreeRTOS.org/a00111.html). If an event group is created using xEventGroupCreateStatic() then the application writer must instead provide the memory that will get used by the event group. xEventGroupCreateStatic() therefore allows an event group to be created without using any dynamic memory allocation. Although event groups are not related to ticks, for internal implementation reasons the number of bits available for use in an event group is dependent on the configUSE_16_BIT_TICKS setting in FreeRTOSConfig.h. If configUSE_16_BIT_TICKS is 1 then each event group contains 8 usable bits (bit 0 to bit 7). If configUSE_16_BIT_TICKS is set to 0 then each event group has 24 usable bits (bit 0 to bit 23). The EventBits_t type is used to store event bits within an event group. Example usage:
{c}
// StaticEventGroup_t is a publicly accessible structure that has the same
// size and alignment requirements as the real event group structure. It is
// provided as a mechanism for applications to know the size of the event
// group (which is dependent on the architecture and configuration file
// settings) without breaking the strict data hiding policy by exposing the
// real event group internals. This StaticEventGroup_t variable is passed
// into the xSemaphoreCreateEventGroupStatic() function and is used to store
// the event group's data structures
StaticEventGroup_t xEventGroupBuffer;
// Create the event group without dynamically allocating any memory.
xEventGroup = xEventGroupCreateStatic( &xEventGroupBuffer );
Retrieve a pointer to a statically created event groups's data structure buffer. It is the same buffer that is supplied at the time of creation.
Utility function to select the highest priority and runnable task for the current core.
Get the total execution of a particular core's idle task This function is equivalent to ulTaskGetIdleRunTimeCounter() but queries the idle task of a particular core.
Get the percentage run time of a particular core's idle task This function is equivalent to ulTaskGetIdleRunTimePercent() but queries the idle task of a particular core.
Check if in ISR context from High priority ISRs - Called from High priority ISR - Checks if the previous context (before high priority interrupt) was in ISR context (meaning low/med priority)
Deletes a task previously created using xTaskCreateWithCaps() or xTaskCreatePinnedToCoreWithCaps()
A version of uxQueueMessagesWaiting() that can be called from an ISR. Return the number of messages stored in a queue.
Hook function called on entry to tickless idle - Implemented in pm_impl.c
FreeRTOS compliant version of vPortEnterCritical() Compliant version of vPortEnterCritical() will ensure that this is called from a task context only. An abort is called otherwise.
Create a new task and add it to the list of tasks that are ready to run. Internally, within the FreeRTOS implementation, tasks use two blocks of memory. The first block is used to hold the task's data structures. The second block is used by the task as its stack. If a task is created using xTaskCreate() then both blocks of memory are automatically dynamically allocated inside the xTaskCreate() function. (see https://www.FreeRTOS.org/a00111.html). If a task is created using xTaskCreateStatic() then the application writer must provide the required memory. xTaskCreateStatic() therefore allows a task to be created without using any dynamic memory allocation. Example usage:
{c}
// Dimensions the buffer that the task being created will use as its stack.
// NOTE: This is the number of bytes the stack will hold, not the number of
// words as found in vanilla FreeRTOS.
#define STACK_SIZE 200
// Structure that will hold the TCB of the task being created.
StaticTask_t xTaskBuffer;
// Buffer that the task being created will use as its stack. Note this is
// an array of StackType_t variables. The size of StackType_t is dependent on
// the RTOS port.
StackType_t xStack[ STACK_SIZE ];
// Function that implements the task being created.
void vTaskCode( void * pvParameters )
{
// The parameter value is expected to be 1 as 1 is passed in the
// pvParameters value in the call to xTaskCreateStatic().
configASSERT( ( uint32_t ) pvParameters == 1UL );
for( ;; )
{
// Task code goes here.
}
}
// Function that creates a task.
void vOtherFunction( void )
{
TaskHandle_t xHandle = NULL;
// Create the task without using any dynamic memory allocation.
xHandle = xTaskCreateStatic(
vTaskCode, // Function that implements the task.
"NAME", // Text name for the task.
STACK_SIZE, // Stack size in bytes.
( void * ) 1, // Parameter passed into the task.
tskIDLE_PRIORITY,// Priority at which the task is created.
xStack, // Array to use as the task's stack.
&xTaskBuffer ); // Variable to hold the task's data structure.
// puxStackBuffer and pxTaskBuffer were not NULL, so the task will have
// been created, and xHandle will be the task's handle. Use the handle
// to suspend the task.
vTaskSuspend( xHandle );
}
FreeRTOS compliant version of vPortExitCritical() Compliant version of vPortExitCritical() will ensure that this is called from a task context only. An abort is called otherwise.
Set a watchpoint to watch the last 32 bytes of the stack Callback to set a watchpoint on the end of the stack. Called every context switch to change the stack watchpoint around.
@endcond INCLUDE_xTaskAbortDelay must be defined as 1 in FreeRTOSConfig.h for this function to be available. A task will enter the Blocked state when it is waiting for an event. The event it is waiting for can be a temporal event (waiting for a time), such as when vTaskDelay() is called, or an event on an object, such as when xQueueReceive() or ulTaskNotifyTake() is called. If the handle of a task that is in the Blocked state is used in a call to xTaskAbortDelay() then the task will leave the Blocked state, and return from whichever function call placed the task into the Blocked state. There is no 'FromISR' version of this function as an interrupt would need to know which object a task was blocked on in order to know which actions to take. For example, if the task was blocked on a queue the interrupt handler would then need to know if the queue was locked.
A version of uxTaskPriorityGet() that can be used from an ISR.
INCLUDE_xTaskResumeFromISR must be defined as 1 for this function to be available. See the configuration section for more information. An implementation of vTaskResume() that can be called from within an ISR. A task that has been suspended by one or more calls to vTaskSuspend () will be made available for running again by a single call to xTaskResumeFromISR (). xTaskResumeFromISR() should not be used to synchronise a task with an interrupt if there is a chance that the interrupt could arrive prior to the task being suspended - as this can lead to interrupts being missed. Use of a semaphore as a synchronisation mechanism would avoid this eventuality.
NOTE: At the time of writing only the x86 real mode port, which runs on a PC in place of DOS, implements this function. Stops the real time kernel tick. All created tasks will be automatically deleted and multitasking (either preemptive or cooperative) will stop. Execution then resumes from the point where vTaskStartScheduler () was called, as if vTaskStartScheduler () had just returned. See the demo application file main. c in the demo/PC directory for an example that uses vTaskEndScheduler (). vTaskEndScheduler () requires an exit function to be defined within the portable layer (see vPortEndScheduler () in port. c for the PC port). This performs hardware specific operations such as stopping the kernel tick. vTaskEndScheduler () will cause all of the resources allocated by the kernel to be freed - but will not free resources allocated by application tasks. Example usage:
{c}
void vTaskCode( void * pvParameters )
{
for( ;; )
{
// Task code goes here.
// At some point we want to end the real time kernel processing
// so call ...
vTaskEndScheduler ();
}
}
void vAFunction( void )
{
// Create at least one task before starting the kernel.
xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, NULL );
// Start the real time kernel with preemption.
vTaskStartScheduler ();
// Will only get here when the vTaskCode () task has called
// vTaskEndScheduler (). When we get here we are back to single task
// execution.
}
NOTE: This function takes a relatively long time to complete and should be used sparingly.
See https://www.FreeRTOS.org/RTOS-task-notifications.html for details. configUSE_TASK_NOTIFICATIONS must be undefined or defined as 1 for these functions to be available. Each task has a private array of "notification values" (or 'notifications'), each of which is a 32-bit unsigned integer (uint32_t). The constant configTASK_NOTIFICATION_ARRAY_ENTRIES sets the number of indexes in the array, and (for backward compatibility) defaults to 1 if left undefined. Prior to FreeRTOS V10.4.0 there was only one notification value per task. ulTaskNotifyValueClearIndexed() clears the bits specified by the ulBitsToClear bit mask in the notification value at array index uxIndexToClear of the task referenced by xTask. Backward compatibility information: Prior to FreeRTOS V10.4.0 each task had a single "notification value", and all task notification API functions operated on that value. Replacing the single notification value with an array of notification values necessitated a new set of API functions that could address specific notifications within the array. ulTaskNotifyValueClear() is the original API function, and remains backward compatible by always operating on the notification value at index 0 within the array. Calling ulTaskNotifyValueClear() is equivalent to calling ulTaskNotifyValueClearIndexed() with the uxIndexToClear parameter set to 0.
INCLUDE_uxTaskGetStackHighWaterMark2 must be set to 1 in FreeRTOSConfig.h for this function to be available. Returns the high water mark of the stack associated with xTask. That is, the minimum free stack space there has been (in words, so on a 32 bit machine a value of 1 means 4 bytes) since the task started. The smaller the returned number the closer the task has come to overflowing its stack. uxTaskGetStackHighWaterMark() and uxTaskGetStackHighWaterMark2() are the same except for their return type. Using configSTACK_DEPTH_TYPE allows the user to determine the return type. It gets around the problem of the value overflowing on 8-bit types without breaking backward compatibility for applications that expect an 8-bit return type.
Each task contains an array of pointers that is dimensioned by the configNUM_THREAD_LOCAL_STORAGE_POINTERS setting in FreeRTOSConfig.h. The kernel does not use the pointers itself, so the application writer can use the pointers for any purpose they wish. The following two functions are used to set and query a pointer respectively.
configGENERATE_RUN_TIME_STATS and configUSE_STATS_FORMATTING_FUNCTIONS must both be defined as 1 for this function to be available. The application must also then provide definitions for portCONFIGURE_TIMER_FOR_RUN_TIME_STATS() and portGET_RUN_TIME_COUNTER_VALUE() to configure a peripheral timer/counter and return the timers current count value respectively. The counter should be at least 10 times the frequency of the tick count. NOTE 1: This function will disable interrupts for its duration. It is not intended for normal application runtime use but as a debug aid. Setting configGENERATE_RUN_TIME_STATS to 1 will result in a total accumulated execution time being stored for each task. The resolution of the accumulated time value depends on the frequency of the timer configured by the portCONFIGURE_TIMER_FOR_RUN_TIME_STATS() macro. Calling vTaskGetRunTimeStats() writes the total execution time of each task into a buffer, both as an absolute count value and as a percentage of the total system execution time. NOTE 2: This function is provided for convenience only, and is used by many of the demo applications. Do not consider it to be part of the scheduler. vTaskGetRunTimeStats() calls uxTaskGetSystemState(), then formats part of the uxTaskGetSystemState() output into a human readable table that displays the amount of time each task has spent in the Running state in both absolute and percentage terms. vTaskGetRunTimeStats() has a dependency on the sprintf() C library function that might bloat the code size, use a lot of stack, and provide different results on different platforms. An alternative, tiny, third party, and limited functionality implementation of sprintf() is provided in many of the FreeRTOS/Demo sub-directories in a file called printf-stdarg.c (note printf-stdarg.c does not provide a full snprintf() implementation!). It is recommended that production systems call uxTaskGetSystemState() directly to get access to raw stats data, rather than indirectly through a call to vTaskGetRunTimeStats().
configGENERATE_RUN_TIME_STATS, configUSE_STATS_FORMATTING_FUNCTIONS and INCLUDE_xTaskGetIdleTaskHandle must all be defined as 1 for these functions to be available. The application must also then provide definitions for portCONFIGURE_TIMER_FOR_RUN_TIME_STATS() and portGET_RUN_TIME_COUNTER_VALUE() to configure a peripheral timer/counter and return the timers current count value respectively. The counter should be at least 10 times the frequency of the tick count. Setting configGENERATE_RUN_TIME_STATS to 1 will result in a total accumulated execution time being stored for each task. The resolution of the accumulated time value depends on the frequency of the timer configured by the portCONFIGURE_TIMER_FOR_RUN_TIME_STATS() macro. While uxTaskGetSystemState() and vTaskGetRunTimeStats() writes the total execution time of each task into a buffer, ulTaskGetIdleRunTimeCounter() returns the total execution time of just the idle task and ulTaskGetIdleRunTimePercent() returns the percentage of the CPU time used by just the idle task. Note the amount of idle time is only a good measure of the slack time in a system if there are no other tasks executing at the idle priority, tickless idle is not used, and configIDLE_SHOULD_YIELD is set to 0.
A version of xQueuePeek() that can be called from an interrupt service routine (ISR). Receive an item from a queue without removing the item from the queue. The item is received by copy so a buffer of adequate size must be provided. The number of bytes copied into the buffer was defined when the queue was created. Successfully received items remain on the queue so will be returned again by the next call, or a call to xQueueReceive().
This function corrects the tick count value after the application code has held interrupts disabled for an extended period resulting in tick interrupts having been missed. This function is similar to vTaskStepTick(), however, unlike vTaskStepTick(), xTaskCatchUpTicks() may move the tick count forward past a time at which a task should be removed from the blocked state. That means tasks may have to be removed from the blocked state as the tick count is moved.
A version of xQueueSelectFromSet() that can be used from an ISR.
Sends bytes to a stream buffer. The bytes are copied into the stream buffer. ***NOTE***: Uniquely among FreeRTOS objects, the stream buffer implementation (so also the message buffer implementation, as message buffers are built on top of stream buffers) assumes there is only one task or interrupt that will write to the buffer (the writer), and only one task or interrupt that will read from the buffer (the reader). It is safe for the writer and reader to be different tasks or interrupts, but, unlike other FreeRTOS objects, it is not safe to have multiple different writers or multiple different readers. If there are to be multiple different writers then the application writer must place each call to a writing API function (such as xStreamBufferSend()) inside a critical section and set the send block time to 0. Likewise, if there are to be multiple different readers then the application writer must place each call to a reading API function (such as xStreamBufferReceive()) inside a critical section and set the receive block time to 0. Use xStreamBufferSend() to write to a stream buffer from a task. Use xStreamBufferSendFromISR() to write to a stream buffer from an interrupt service routine (ISR). Example use:
{c}
void vAFunction( StreamBufferHandle_t xStreamBuffer )
{
size_t xBytesSent;
uint8_t ucArrayToSend[] = { 0, 1, 2, 3 };
char *pcStringToSend = "String to send";
const TickType_t x100ms = pdMS_TO_TICKS( 100 );
// Send an array to the stream buffer, blocking for a maximum of 100ms to
// wait for enough space to be available in the stream buffer.
xBytesSent = xStreamBufferSend( xStreamBuffer, ( void * ) ucArrayToSend, sizeof( ucArrayToSend ), x100ms );
if( xBytesSent != sizeof( ucArrayToSend ) )
{
// The call to xStreamBufferSend() times out before there was enough
// space in the buffer for the data to be written, but it did
// successfully write xBytesSent bytes.
}
// Send the string to the stream buffer. Return immediately if there is not
// enough space in the buffer.
xBytesSent = xStreamBufferSend( xStreamBuffer, ( void * ) pcStringToSend, strlen( pcStringToSend ), 0 );
if( xBytesSent != strlen( pcStringToSend ) )
{
// The entire string could not be added to the stream buffer because
// there was not enough free space in the buffer, but xBytesSent bytes
// were sent. Could try again to send the remaining bytes.
}
}
Interrupt safe version of the API function that sends a stream of bytes to the stream buffer. ***NOTE***: Uniquely among FreeRTOS objects, the stream buffer implementation (so also the message buffer implementation, as message buffers are built on top of stream buffers) assumes there is only one task or interrupt that will write to the buffer (the writer), and only one task or interrupt that will read from the buffer (the reader). It is safe for the writer and reader to be different tasks or interrupts, but, unlike other FreeRTOS objects, it is not safe to have multiple different writers or multiple different readers. If there are to be multiple different writers then the application writer must place each call to a writing API function (such as xStreamBufferSend()) inside a critical section and set the send block time to 0. Likewise, if there are to be multiple different readers then the application writer must place each call to a reading API function (such as xStreamBufferReceive()) inside a critical section and set the receive block time to 0. Use xStreamBufferSend() to write to a stream buffer from a task. Use xStreamBufferSendFromISR() to write to a stream buffer from an interrupt service routine (ISR). Example use:
{c}
// A stream buffer that has already been created.
StreamBufferHandle_t xStreamBuffer;
void vAnInterruptServiceRoutine( void )
{
size_t xBytesSent;
char *pcStringToSend = "String to send";
BaseType_t xHigherPriorityTaskWoken = pdFALSE; // Initialised to pdFALSE.
// Attempt to send the string to the stream buffer.
xBytesSent = xStreamBufferSendFromISR( xStreamBuffer,
( void * ) pcStringToSend,
strlen( pcStringToSend ),
&xHigherPriorityTaskWoken );
if( xBytesSent != strlen( pcStringToSend ) )
{
// There was not enough free space in the stream buffer for the entire
// string to be written, ut xBytesSent bytes were written.
}
// If xHigherPriorityTaskWoken was set to pdTRUE inside
// xStreamBufferSendFromISR() then a task that has a priority above the
// priority of the currently executing task was unblocked and a context
// switch should be performed to ensure the ISR returns to the unblocked
// task. In most FreeRTOS ports this is done by simply passing
// xHigherPriorityTaskWoken into portYIELD_FROM_ISR(), which will test the
// variables value, and perform the context switch if necessary. Check the
// documentation for the port in use for port specific instructions.
portYIELD_FROM_ISR( xHigherPriorityTaskWoken );
}
Receives bytes from a stream buffer. ***NOTE***: Uniquely among FreeRTOS objects, the stream buffer implementation (so also the message buffer implementation, as message buffers are built on top of stream buffers) assumes there is only one task or interrupt that will write to the buffer (the writer), and only one task or interrupt that will read from the buffer (the reader). It is safe for the writer and reader to be different tasks or interrupts, but, unlike other FreeRTOS objects, it is not safe to have multiple different writers or multiple different readers. If there are to be multiple different writers then the application writer must place each call to a writing API function (such as xStreamBufferSend()) inside a critical section and set the send block time to 0. Likewise, if there are to be multiple different readers then the application writer must place each call to a reading API function (such as xStreamBufferReceive()) inside a critical section and set the receive block time to 0. Use xStreamBufferReceive() to read from a stream buffer from a task. Use xStreamBufferReceiveFromISR() to read from a stream buffer from an interrupt service routine (ISR). Example use:
{c}
void vAFunction( StreamBuffer_t xStreamBuffer )
{
uint8_t ucRxData[ 20 ];
size_t xReceivedBytes;
const TickType_t xBlockTime = pdMS_TO_TICKS( 20 );
// Receive up to another sizeof( ucRxData ) bytes from the stream buffer.
// Wait in the Blocked state (so not using any CPU processing time) for a
// maximum of 100ms for the full sizeof( ucRxData ) number of bytes to be
// available.
xReceivedBytes = xStreamBufferReceive( xStreamBuffer,
( void * ) ucRxData,
sizeof( ucRxData ),
xBlockTime );
if( xReceivedBytes > 0 )
{
// A ucRxData contains another xReceivedBytes bytes of data, which can
// be processed here....
}
}
An interrupt safe version of the API function that receives bytes from a stream buffer. Use xStreamBufferReceive() to read bytes from a stream buffer from a task. Use xStreamBufferReceiveFromISR() to read bytes from a stream buffer from an interrupt service routine (ISR). Example use:
{c}
// A stream buffer that has already been created.
StreamBuffer_t xStreamBuffer;
void vAnInterruptServiceRoutine( void )
{
uint8_t ucRxData[ 20 ];
size_t xReceivedBytes;
BaseType_t xHigherPriorityTaskWoken = pdFALSE; // Initialised to pdFALSE.
// Receive the next stream from the stream buffer.
xReceivedBytes = xStreamBufferReceiveFromISR( xStreamBuffer,
( void * ) ucRxData,
sizeof( ucRxData ),
&xHigherPriorityTaskWoken );
if( xReceivedBytes > 0 )
{
// ucRxData contains xReceivedBytes read from the stream buffer.
// Process the stream here....
}
// If xHigherPriorityTaskWoken was set to pdTRUE inside
// xStreamBufferReceiveFromISR() then a task that has a priority above the
// priority of the currently executing task was unblocked and a context
// switch should be performed to ensure the ISR returns to the unblocked
// task. In most FreeRTOS ports this is done by simply passing
// xHigherPriorityTaskWoken into portYIELD_FROM_ISR(), which will test the
// variables value, and perform the context switch if necessary. Check the
// documentation for the port in use for port specific instructions.
portYIELD_FROM_ISR( xHigherPriorityTaskWoken );
}
Queries a stream buffer to see if it is full. A stream buffer is full if it does not have any free space, and therefore cannot accept any more data.
Queries a stream buffer to see if it is empty. A stream buffer is empty if it does not contain any data.
Resets a stream buffer to its initial, empty, state. Any data that was in the stream buffer is discarded. A stream buffer can only be reset if there are no tasks blocked waiting to either send to or receive from the stream buffer.
Queries a stream buffer to see how much data it contains, which is equal to the number of bytes that can be read from the stream buffer before the stream buffer would be empty.
A stream buffer's trigger level is the number of bytes that must be in the stream buffer before a task that is blocked on the stream buffer to wait for data is moved out of the blocked state. For example, if a task is blocked on a read of an empty stream buffer that has a trigger level of 1 then the task will be unblocked when a single byte is written to the buffer or the task's block time expires. As another example, if a task is blocked on a read of an empty stream buffer that has a trigger level of 10 then the task will not be unblocked until the stream buffer contains at least 10 bytes or the task's block time expires. If a reading task's block time expires before the trigger level is reached then the task will still receive however many bytes are actually available. Setting a trigger level of 0 will result in a trigger level of 1 being used. It is not valid to specify a trigger level that is greater than the buffer size. A trigger level is set when the stream buffer is created, and can be modified using xStreamBufferSetTriggerLevel().
For advanced users only. The sbSEND_COMPLETED() macro is called from within the FreeRTOS APIs when data is sent to a message buffer or stream buffer. If there was a task that was blocked on the message or stream buffer waiting for data to arrive then the sbSEND_COMPLETED() macro sends a notification to the task to remove it from the Blocked state. xStreamBufferSendCompletedFromISR() does the same thing. It is provided to enable application writers to implement their own version of sbSEND_COMPLETED(), and MUST NOT BE USED AT ANY OTHER TIME. See the example implemented in FreeRTOS/Demo/Minimal/MessageBufferAMP.c for additional information.
For advanced users only. The sbRECEIVE_COMPLETED() macro is called from within the FreeRTOS APIs when data is read out of a message buffer or stream buffer. If there was a task that was blocked on the message or stream buffer waiting for data to arrive then the sbRECEIVE_COMPLETED() macro sends a notification to the task to remove it from the Blocked state. xStreamBufferReceiveCompletedFromISR() does the same thing. It is provided to enable application writers to implement their own version of sbRECEIVE_COMPLETED(), and MUST NOT BE USED AT ANY OTHER TIME. See the example implemented in FreeRTOS/Demo/Minimal/MessageBufferAMP.c for additional information.
@endcond Queue sets provide a mechanism to allow a task to block (pend) on a read operation from multiple queues or semaphores simultaneously. See FreeRTOS/Source/Demo/Common/Minimal/QueueSet.c for an example using this function. A queue set must be explicitly created using a call to xQueueCreateSet() before it can be used. Once created, standard FreeRTOS queues and semaphores can be added to the set using calls to xQueueAddToSet(). xQueueSelectFromSet() is then used to determine which, if any, of the queues or semaphores contained in the set is in a state where a queue read or semaphore take operation would be successful. Note 1: See the documentation on https://www.FreeRTOS.org/RTOS-queue-sets.html for reasons why queue sets are very rarely needed in practice as there are simpler methods of blocking on multiple objects. Note 2: Blocking on a queue set that contains a mutex will not cause the mutex holder to inherit the priority of the blocked task. Note 3: An additional 4 bytes of RAM is required for each space in a every queue added to a queue set. Therefore counting semaphores that have a high maximum count value should not be added to a queue set. Note 4: A receive (in the case of a queue) or take (in the case of a semaphore) operation must not be performed on a member of a queue set unless a call to xQueueSelectFromSet() has first returned a handle to that set member.
Adds a queue or semaphore to a queue set that was previously created by a call to xQueueCreateSet(). See FreeRTOS/Source/Demo/Common/Minimal/QueueSet.c for an example using this function. Note 1: A receive (in the case of a queue) or take (in the case of a semaphore) operation must not be performed on a member of a queue set unless a call to xQueueSelectFromSet() has first returned a handle to that set member.
Removes a queue or semaphore from a queue set. A queue or semaphore can only be removed from a set if the queue or semaphore is empty. See FreeRTOS/Source/Demo/Common/Minimal/QueueSet.c for an example using this function.
xQueueSelectFromSet() selects from the members of a queue set a queue or semaphore that either contains data (in the case of a queue) or is available to take (in the case of a semaphore). xQueueSelectFromSet() effectively allows a task to block (pend) on a read operation on all the queues and semaphores in a queue set simultaneously. See FreeRTOS/Source/Demo/Common/Minimal/QueueSet.c for an example using this function. Note 1: See the documentation on https://www.FreeRTOS.org/RTOS-queue-sets.html for reasons why queue sets are very rarely needed in practice as there are simpler methods of blocking on multiple objects. Note 2: Blocking on a queue set that contains a mutex will not cause the mutex holder to inherit the priority of the blocked task. Note 3: A receive (in the case of a queue) or take (in the case of a semaphore) operation must not be performed on a member of a queue set unless a call to xQueueSelectFromSet() has first returned a handle to that set member.
Creates a new software timer instance, and returns a handle by which the created software timer can be referenced. Internally, within the FreeRTOS implementation, software timers use a block of memory, in which the timer data structure is stored. If a software timer is created using xTimerCreate() then the required memory is automatically dynamically allocated inside the xTimerCreate() function. (see https://www.FreeRTOS.org/a00111.html). If a software timer is created using xTimerCreateStatic() then the application writer must provide the memory that will get used by the software timer. xTimerCreateStatic() therefore allows a software timer to be created without using any dynamic memory allocation. Timers are created in the dormant state. The xTimerStart(), xTimerReset(), xTimerStartFromISR(), xTimerResetFromISR(), xTimerChangePeriod() and xTimerChangePeriodFromISR() API functions can all be used to transition a timer into the active state. Example usage: @verbatim // The buffer used to hold the software timer's data structure. static StaticTimer_t xTimerBuffer; // A variable that will be incremented by the software timer's callback // function. UBaseType_t uxVariableToIncrement = 0; // A software timer callback function that increments a variable passed to // it when the software timer was created. After the 5th increment the // callback function stops the software timer. static void prvTimerCallback( TimerHandle_t xExpiredTimer ) { UBaseType_t *puxVariableToIncrement; BaseType_t xReturned; // Obtain the address of the variable to increment from the timer ID. puxVariableToIncrement = ( UBaseType_t * ) pvTimerGetTimerID( xExpiredTimer ); // Increment the variable to show the timer callback has executed. ( *puxVariableToIncrement )++; // If this callback has executed the required number of times, stop the // timer. if( *puxVariableToIncrement == 5 ) { // This is called from a timer callback so must not block. xTimerStop( xExpiredTimer, staticDONT_BLOCK ); } } void main( void ) { // Create the software time. xTimerCreateStatic() has an extra parameter // than the normal xTimerCreate() API function. The parameter is a pointer // to the StaticTimer_t structure that will hold the software timer // structure. If the parameter is passed as NULL then the structure will be // allocated dynamically, just as if xTimerCreate() had been called. xTimer = xTimerCreateStatic( "T1", // Text name for the task. Helps debugging only. Not used by FreeRTOS. xTimerPeriod, // The period of the timer in ticks. pdTRUE, // This is an auto-reload timer. ( void * ) &uxVariableToIncrement, // A variable incremented by the software timer's callback function prvTimerCallback, // The function to execute when the timer expires. &xTimerBuffer ); // The buffer that will hold the software timer structure. // The scheduler has not started yet so a block time is not used. xReturned = xTimerStart( xTimer, 0 ); // ... // Create tasks here. // ... // Starting the scheduler will start the timers running as they have already // been set into the active state. vTaskStartScheduler(); // Should not reach here. for( ;; ); } @endverbatim
Simply returns the handle of the timer service/daemon task. It it not valid to call xTimerGetTimerDaemonTaskHandle() before the scheduler has been started.
Used to defer the execution of a function to the RTOS daemon task (the timer service task, hence this function is implemented in timers.c and is prefixed with 'Timer').
Returns the name that was assigned to a timer when the timer was created.
Updates a timer to be either an auto-reload timer, in which case the timer automatically resets itself each time it expires, or a one-shot timer, in which case the timer will only expire once unless it is manually restarted.
Queries a timer to determine if it is an auto-reload timer, in which case the timer automatically resets itself each time it expires, or a one-shot timer, in which case the timer will only expire once unless it is manually restarted.
Returns the time in ticks at which the timer will expire. If this is less than the current tick count then the expiry time has overflowed from the current time.
Retrieve pointer to a statically created timer's data structure buffer. This is the same buffer that is supplied at the time of creation.
Atomically set bits within an event group, then wait for a combination of bits to be set within the same event group. This functionality is typically used to synchronise multiple tasks, where each task has to wait for the other tasks to reach a synchronisation point before proceeding. This function cannot be used from an interrupt. The function will return before its block time expires if the bits specified by the uxBitsToWait parameter are set, or become set within that time. In this case all the bits specified by uxBitsToWait will be automatically cleared before the function returns. Example usage:
{c}
// Bits used by the three tasks.
#define TASK_0_BIT ( 1 << 0 )
#define TASK_1_BIT ( 1 << 1 )
#define TASK_2_BIT ( 1 << 2 )
#define ALL_SYNC_BITS ( TASK_0_BIT | TASK_1_BIT | TASK_2_BIT )
// Use an event group to synchronise three tasks. It is assumed this event
// group has already been created elsewhere.
EventGroupHandle_t xEventBits;
void vTask0( void *pvParameters )
{
EventBits_t uxReturn;
TickType_t xTicksToWait = 100 / portTICK_PERIOD_MS;
for( ;; )
{
// Perform task functionality here.
// Set bit 0 in the event flag to note this task has reached the
// sync point. The other two tasks will set the other two bits defined
// by ALL_SYNC_BITS. All three tasks have reached the synchronisation
// point when all the ALL_SYNC_BITS are set. Wait a maximum of 100ms
// for this to happen.
uxReturn = xEventGroupSync( xEventBits, TASK_0_BIT, ALL_SYNC_BITS, xTicksToWait );
if( ( uxReturn & ALL_SYNC_BITS ) == ALL_SYNC_BITS )
{
// All three tasks reached the synchronisation point before the call
// to xEventGroupSync() timed out.
}
}
}
void vTask1( void *pvParameters )
{
for( ;; )
{
// Perform task functionality here.
// Set bit 1 in the event flag to note this task has reached the
// synchronisation point. The other two tasks will set the other two
// bits defined by ALL_SYNC_BITS. All three tasks have reached the
// synchronisation point when all the ALL_SYNC_BITS are set. Wait
// indefinitely for this to happen.
xEventGroupSync( xEventBits, TASK_1_BIT, ALL_SYNC_BITS, portMAX_DELAY );
// xEventGroupSync() was called with an indefinite block time, so
// this task will only reach here if the synchronisation was made by all
// three tasks, so there is no need to test the return value.
}
}
void vTask2( void *pvParameters )
{
for( ;; )
{
// Perform task functionality here.
// Set bit 2 in the event flag to note this task has reached the
// synchronisation point. The other two tasks will set the other two
// bits defined by ALL_SYNC_BITS. All three tasks have reached the
// synchronisation point when all the ALL_SYNC_BITS are set. Wait
// indefinitely for this to happen.
xEventGroupSync( xEventBits, TASK_2_BIT, ALL_SYNC_BITS, portMAX_DELAY );
// xEventGroupSync() was called with an indefinite block time, so
// this task will only reach here if the synchronisation was made by all
// three tasks, so there is no need to test the return value.
}
}
A version of xEventGroupGetBits() that can be called from an ISR.
Deletes an event group previously created using xEventGroupCreateWithCaps()
Returns the start of the stack associated with xTask. Returns the lowest stack memory address, regardless of whether the stack grows up or down. [refactor-todo] Change return type to StackType_t (IDF-8158)
Creates an event group with specific memory capabilities This function is similar to xEventGroupCreate(), except that it allows the memory allocated for the event group to have specific capabilities (e.g., MALLOC_CAP_INTERNAL).
Get a void pointer to the current TCB of a particular core
Handler of SysTick The function is called from: - _frxt_timer_int for xtensa with CONFIG_FREERTOS_SYSTICK_USES_CCOUNT - SysTickIsrHandler for xtensa with CONFIG_FREERTOS_SYSTICK_USES_SYSTIMER - SysTickIsrHandler for riscv
INCLUDE_vTaskPrioritySet must be defined as 1 for this function to be available. See the configuration section for more information. Saves the current priority and current base priority of a task, then raises the task's current and base priority to uxNewPriority if uxNewPriority is of a higher priority. Once a task's priority has been raised with this function, the priority can be restored by calling prvTaskPriorityRestore() - Note that this function differs from vTaskPrioritySet() as the task's current priority will be modified even if the task has already inherited a priority. - This function is intended for special circumstance where a task must be forced immediately to a higher priority. For configUSE_MUTEXES == 0: A context switch will occur before the function returns if the priority being set is higher than the priority of the currently executing task.
INCLUDE_vTaskPrioritySet must be defined as 1 for this function to be available. See the configuration section for more information. Restore a task's priority that was previously raised by prvTaskPriorityRaise(). For configUSE_MUTEXES == 0: A context switch will occur before the function returns if the priority being set is higher than the priority of the currently executing task.
Get the total count of task lists. The count includes both the ready task lists (based on priority) and non-ready task lists.
Get the task list from state lists by index - This function returns the task list based on the specified index. - The index is relative to the below order of the task state lists - Ready lists (highest to lowers priority) - Pending ready list(s) - Delayed list 1 - Delayed list 2 - Waiting termination list - Suspended list
Initialize the task's starting interrupt stack frame This function initializes the task's starting interrupt stack frame. The dispatcher will use this stack frame in a context restore routine. Therefore, the starting stack frame must be initialized as if the task was interrupted right before its first instruction is called. - The stack frame is allocated to a 16-byte aligned address - The THREADPTR register is saved in the extra storage area of the stack frame. This is also initialized
Allocate and initialize coprocessor save area on the stack This function allocates the coprocessor save area on the stack (sized XT_CP_SIZE) which includes... - Individual save areas for each coprocessor (size XT_CPx_SA, inclusive of each area's alignment) - Coprocessor context switching flags (e.g., XT_CPENABLE, XT_CPSTORED, XT_CP_CS_ST, XT_CP_ASA). The coprocessor save area is aligned to a 16-byte boundary. The coprocessor context switching flags are then initialized
Allocate and initialize GCC TLS area This function allocates and initializes the area on the stack used to store GCC TLS (Thread Local Storage) variables. - The area's size is derived from the TLS section's linker variables, and rounded up to a multiple of 16 bytes - The allocated area is aligned to a 16-byte aligned address - The TLS variables in the area are then initialized Each task access the TLS variables using the THREADPTR register plus an offset to obtain the address of the variable. The value for the THREADPTR register is also calculated by this function, and that value should be use to initialize the THREADPTR register.
A version of xEventGroupClearBits() that can be called from an interrupt. Setting bits in an event group is not a deterministic operation because there are an unknown number of tasks that may be waiting for the bit or bits being set. FreeRTOS does not allow nondeterministic operations to be performed while interrupts are disabled, so protects event groups that are accessed from tasks by suspending the scheduler rather than disabling interrupts. As a result event groups cannot be accessed directly from an interrupt service routine. Therefore xEventGroupClearBitsFromISR() sends a message to the timer task to have the clear operation performed in the context of the timer task. Example usage:
{c}
#define BIT_0 ( 1 << 0 )
#define BIT_4 ( 1 << 4 )
// An event group which it is assumed has already been created by a call to
// xEventGroupCreate().
EventGroupHandle_t xEventGroup;
void anInterruptHandler( void )
{
// Clear bit 0 and bit 4 in xEventGroup.
xResult = xEventGroupClearBitsFromISR(
xEventGroup, // The event group being updated.
BIT_0 | BIT_4 ); // The bits being set.
if( xResult == pdPASS )
{
// The message was posted successfully.
portYIELD_FROM_ISR(pdTRUE);
}
}
A version of xEventGroupSetBits() that can be called from an interrupt. Setting bits in an event group is not a deterministic operation because there are an unknown number of tasks that may be waiting for the bit or bits being set. FreeRTOS does not allow nondeterministic operations to be performed in interrupts or from critical sections. Therefore xEventGroupSetBitsFromISR() sends a message to the timer task to have the set operation performed in the context of the timer task - where a scheduler lock is used in place of a critical section. Example usage:
{c}
#define BIT_0 ( 1 << 0 )
#define BIT_4 ( 1 << 4 )
// An event group which it is assumed has already been created by a call to
// xEventGroupCreate().
EventGroupHandle_t xEventGroup;
void anInterruptHandler( void )
{
BaseType_t xHigherPriorityTaskWoken, xResult;
// xHigherPriorityTaskWoken must be initialised to pdFALSE.
xHigherPriorityTaskWoken = pdFALSE;
// Set bit 0 and bit 4 in xEventGroup.
xResult = xEventGroupSetBitsFromISR(
xEventGroup, // The event group being updated.
BIT_0 | BIT_4 // The bits being set.
&xHigherPriorityTaskWoken );
// Was the message posted successfully?
if( xResult == pdPASS )
{
// If xHigherPriorityTaskWoken is now set to pdTRUE then a context
// switch should be requested. The macro used is port specific and
// will be either portYIELD_FROM_ISR() or portEND_SWITCHING_ISR() -
// refer to the documentation page for the port being used.
portYIELD_FROM_ISR( xHigherPriorityTaskWoken );
}
}
Creates a task where its stack has specific memory capabilities This function is similar to xTaskCreate(), except that it allows the memory allocated for the task's stack to have specific capabilities (e.g., MALLOC_CAP_SPIRAM). However, the specified capabilities will NOT apply to the task's TCB as a TCB must always be in internal RAM.
Creates a counting semaphore with specific memory capabilities This function is similar to xSemaphoreCreateCounting(), except that it allows the memory allocated for the counting semaphore to have specific capabilities (e.g., MALLOC_CAP_INTERNAL).
Creates a recursive mutex with specific memory capabilities This function is similar to xSemaphoreCreateRecursiveMutex(), except that it allows the memory allocated for the recursive mutex to have specific capabilities (e.g., MALLOC_CAP_INTERNAL).
@endcond Creates a stream buffer with specific memory capabilities This function is similar to xStreamBufferCreate(), except that it allows the memory allocated for the stream buffer to have specific capabilities (e.g., MALLOC_CAP_INTERNAL).
Deletes a stream buffer previously created using xStreamBufferCreateWithCaps()
Creates a message buffer with specific memory capabilities This function is similar to xMessageBufferCreate(), except that it allows the memory allocated for the message buffer to have specific capabilities (e.g., MALLOC_CAP_INTERNAL).
Deletes a stream buffer previously created using xMessageBufferCreateWithCaps()
@endcond Memory regions are assigned to a restricted task when the task is created by a call to xTaskCreateRestricted(). These regions can be redefined using vTaskAllocateMPURegions(). Example usage:
{c}
// Define an array of MemoryRegion_t structures that configures an MPU region
// allowing read/write access for 1024 bytes starting at the beginning of the
// ucOneKByte array. The other two of the maximum 3 definable regions are
// unused so set to zero.
static const MemoryRegion_t xAltRegions[ portNUM_CONFIGURABLE_REGIONS ] =
{
// Base address Length Parameters
{ ucOneKByte, 1024, portMPU_REGION_READ_WRITE },
{ 0, 0, 0 },
{ 0, 0, 0 }
};
void vATask( void *pvParameters )
{
// This task was created such that it has access to certain regions of
// memory as defined by the MPU configuration. At some point it is
// desired that these MPU regions are replaced with that defined in the
// xAltRegions const struct above. Use a call to vTaskAllocateMPURegions()
// for this purpose. NULL is used as the task handle to indicate that this
// function should modify the MPU regions of the calling task.
vTaskAllocateMPURegions( NULL, xAltRegions );
// Now the task can continue its function, but from this point on can only
// access its stack and the ucOneKByte array (unless any other statically
// defined or shared regions have been declared elsewhere).
}
Calls the hook function associated with xTask. Passing xTask as NULL has the effect of calling the Running tasks (the calling task) hook function. pvParameter is passed to the hook function for the task to interpret as it wants. The return value is the value returned by the task hook function registered by the user.
Other commonly used symbols
Name
Location
Summary
Type by which queues are referenced. For example, a call to xQueueCreate() returns an QueueHandle_t variable that can then be used as a parameter to xQueueSend(), xQueueReceive(), etc.
@endcond Type by which tasks are referenced. For example, a call to xTaskCreate returns (via a pointer parameter) an TaskHandle_t variable that can then be used as a parameter to vTaskDelete to delete the task.
Macro to release a semaphore. The semaphore must have previously been created with a call to xSemaphoreCreateBinary(), xSemaphoreCreateMutex() or xSemaphoreCreateCounting(). and obtained using sSemaphoreTake(). This macro must not be used from an ISR. See xSemaphoreGiveFromISR () for an alternative which can be used from an ISR. This macro must also not be used on semaphores created using xSemaphoreCreateRecursiveMutex(). Example usage:
{c}
SemaphoreHandle_t xSemaphore = NULL;
void vATask( void * pvParameters )
{
// Create the semaphore to guard a shared resource.
xSemaphore = vSemaphoreCreateBinary();
if( xSemaphore != NULL )
{
if( xSemaphoreGive( xSemaphore ) != pdTRUE )
{
// We would expect this call to fail because we cannot give
// a semaphore without first "taking" it!
}
// Obtain the semaphore - don't block if the semaphore is not
// immediately available.
if( xSemaphoreTake( xSemaphore, ( TickType_t ) 0 ) )
{
// We now have the semaphore and can access the shared resource.
// ...
// We have finished accessing the shared resource so can free the
// semaphore.
if( xSemaphoreGive( xSemaphore ) != pdTRUE )
{
// We would not expect this call to fail because we must have
// obtained the semaphore to get here.
}
}
}
}
Macro to obtain a semaphore. The semaphore must have previously been created with a call to xSemaphoreCreateBinary(), xSemaphoreCreateMutex() or xSemaphoreCreateCounting(). Example usage:
{c}
SemaphoreHandle_t xSemaphore = NULL;
// A task that creates a semaphore.
void vATask( void * pvParameters )
{
// Create the semaphore to guard a shared resource.
xSemaphore = xSemaphoreCreateBinary();
}
// A task that uses the semaphore.
void vAnotherTask( void * pvParameters )
{
// ... Do other things.
if( xSemaphore != NULL )
{
// See if we can obtain the semaphore. If the semaphore is not available
// wait 10 ticks to see if it becomes free.
if( xSemaphoreTake( xSemaphore, ( TickType_t ) 10 ) == pdTRUE )
{
// We were able to obtain the semaphore and can now access the
// shared resource.
// ...
// We have finished accessing the shared resource. Release the
// semaphore.
xSemaphoreGive( xSemaphore );
}
else
{
// We could not obtain the semaphore and can therefore not access
// the shared resource safely.
}
}
}
An event group is a collection of bits to which an application can assign a meaning. For example, an application may create an event group to convey the status of various CAN bus related events in which bit 0 might mean "A CAN message has been received and is ready for processing", bit 1 might mean "The application has queued a message that is ready for sending onto the CAN network", and bit 2 might mean "It is time to send a SYNC message onto the CAN network" etc. A task can then test the bit values to see which events are active, and optionally enter the Blocked state to wait for a specified bit or a group of specified bits to be active. To continue the CAN bus example, a CAN controlling task can enter the Blocked state (and therefore not consume any processing time) until either bit 0, bit 1 or bit 2 are active, at which time the bit that was actually active would inform the task which action it had to take (process a received message, send a message, or send a SYNC). The event groups implementation contains intelligence to avoid race conditions that would otherwise occur were an application to use a simple variable for the same purpose. This is particularly important with respect to when a bit within an event group is to be cleared, and when bits have to be set and then tested atomically - as is the case where event groups are used to create a synchronisation point between multiple tasks (a 'rendezvous'). Type by which event groups are referenced. For example, a call to xEventGroupCreate() returns an EventGroupHandle_t variable that can then be used as a parameter to other event group functions.
Delete a semaphore. This function must be used with care. For example, do not delete a mutex type semaphore if the mutex is held by a task.
@endcond Type by which software timers are referenced. For example, a call to xTimerCreate() returns an TimerHandle_t variable that can then be used to reference the subject timer in calls to other software timer API functions (for example, xTimerStart(), xTimerReset(), etc.).
Type by which stream buffers are referenced. For example, a call to xStreamBufferCreate() returns an StreamBufferHandle_t variable that can then be used as a parameter to xStreamBufferSend(), xStreamBufferReceive(), etc.
This is a macro that calls xQueueGenericSend(). It is included for backward compatibility with versions of FreeRTOS.org that did not include the xQueueSendToFront() and xQueueSendToBack() macros. It is equivalent to xQueueSendToBack(). Post an item on a queue. The item is queued by copy, not by reference. This function must not be called from an interrupt service routine. See xQueueSendFromISR () for an alternative which may be used in an ISR. Example usage:
{c}
struct AMessage
{
char ucMessageID;
char ucData[ 20 ];
} xMessage;
uint32_t ulVar = 10UL;
void vATask( void *pvParameters )
{
QueueHandle_t xQueue1, xQueue2;
struct AMessage *pxMessage;
// Create a queue capable of containing 10 uint32_t values.
xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) );
// Create a queue capable of containing 10 pointers to AMessage structures.
// These should be passed by pointer as they contain a lot of data.
xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) );
// ...
if( xQueue1 != 0 )
{
// Send an uint32_t. Wait for 10 ticks for space to become
// available if necessary.
if( xQueueSend( xQueue1, ( void * ) &ulVar, ( TickType_t ) 10 ) != pdPASS )
{
// Failed to post the message, even after 10 ticks.
}
}
if( xQueue2 != 0 )
{
// Send a pointer to a struct AMessage object. Don't block if the
// queue is already full.
pxMessage = & xMessage;
xQueueSend( xQueue2, ( void * ) &pxMessage, ( TickType_t ) 0 );
}
// ... Rest of task code.
}
Creates a new binary semaphore instance, and returns a handle by which the new semaphore can be referenced. In many usage scenarios it is faster and more memory efficient to use a direct to task notification in place of a binary semaphore! https://www.FreeRTOS.org/RTOS-task-notifications.html Internally, within the FreeRTOS implementation, binary semaphores use a block of memory, in which the semaphore structure is stored. If a binary semaphore is created using xSemaphoreCreateBinary() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateBinary() function. (see https://www.FreeRTOS.org/a00111.html). If a binary semaphore is created using xSemaphoreCreateBinaryStatic() then the application writer must provide the memory. xSemaphoreCreateBinaryStatic() therefore allows a binary semaphore to be created without using any dynamic memory allocation. The old vSemaphoreCreateBinary() macro is now deprecated in favour of this xSemaphoreCreateBinary() function. Note that binary semaphores created using the vSemaphoreCreateBinary() macro are created in a state such that the first call to 'take' the semaphore would pass, whereas binary semaphores created using xSemaphoreCreateBinary() are created in a state such that the the semaphore must first be 'given' before it can be 'taken'. This type of semaphore can be used for pure synchronisation between tasks or between an interrupt and a task. The semaphore need not be given back once obtained, so one task/interrupt can continuously 'give' the semaphore while another continuously 'takes' the semaphore. For this reason this type of semaphore does not use a priority inheritance mechanism. For an alternative that does use priority inheritance see xSemaphoreCreateMutex(). Example usage:
{c}
SemaphoreHandle_t xSemaphore = NULL;
void vATask( void * pvParameters )
{
// Semaphore cannot be used before a call to xSemaphoreCreateBinary().
// This is a macro so pass the variable in directly.
xSemaphore = xSemaphoreCreateBinary();
if( xSemaphore != NULL )
{
// The semaphore was created successfully.
// The semaphore can now be used.
}
}
@endcond Creates a new queue instance, and returns a handle by which the new queue can be referenced. Internally, within the FreeRTOS implementation, queues use two blocks of memory. The first block is used to hold the queue's data structures. The second block is used to hold items placed into the queue. If a queue is created using xQueueCreate() then both blocks of memory are automatically dynamically allocated inside the xQueueCreate() function. (see https://www.FreeRTOS.org/a00111.html). If a queue is created using xQueueCreateStatic() then the application writer must provide the memory that will get used by the queue. xQueueCreateStatic() therefore allows a queue to be created without using any dynamic memory allocation. https://www.FreeRTOS.org/Embedded-RTOS-Queues.html Example usage:
{c}
struct AMessage
{
char ucMessageID;
char ucData[ 20 ];
};
void vATask( void *pvParameters )
{
QueueHandle_t xQueue1, xQueue2;
// Create a queue capable of containing 10 uint32_t values.
xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) );
if( xQueue1 == 0 )
{
// Queue was not created and must not be used.
}
// Create a queue capable of containing 10 pointers to AMessage structures.
// These should be passed by pointer as they contain a lot of data.
xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) );
if( xQueue2 == 0 )
{
// Queue was not created and must not be used.
}
// ... Rest of task code.
}
Macro to mark the end of a critical code region. Preemptive context switches cannot occur when in a critical region. NOTE: This may alter the stack (depending on the portable implementation) so must be used with care!
@endcond Reset a queue back to its original empty state. The return value is now obsolete and is always set to pdPASS.
Timer functionality is provided by a timer service/daemon task. Many of the public FreeRTOS timer API functions send commands to the timer service task through a queue called the timer command queue. The timer command queue is private to the kernel itself and is not directly accessible to application code. The length of the timer command queue is set by the configTIMER_QUEUE_LENGTH configuration constant. xTimerStop() stops a timer that was previously started using either of the The xTimerStart(), xTimerReset(), xTimerStartFromISR(), xTimerResetFromISR(), xTimerChangePeriod() or xTimerChangePeriodFromISR() API functions. Stopping a timer ensures the timer is not in the active state. The configUSE_TIMERS configuration constant must be set to 1 for xTimerStop() to be available. Example usage: See the xTimerCreate() API function example usage scenario.
Macro to mark the start of a critical code region. Preemptive context switches cannot occur when in a critical region. NOTE: This may alter the stack (depending on the portable implementation) so must be used with care!
Macro representing and unpinned (i.e., "no affinity") task in xCoreID parameters
This is a macro that calls xQueueGenericSendFromISR(). It is included for backward compatibility with versions of FreeRTOS.org that did not include the xQueueSendToBackFromISR() and xQueueSendToFrontFromISR() macros. Post an item to the back of a queue. It is safe to use this function from within an interrupt service routine. Items are queued by copy not reference so it is preferable to only queue small items, especially when called from an ISR. In most cases it would be preferable to store a pointer to the item being queued. Example usage for buffered IO (where the ISR can obtain more than one value per call):
{c}
void vBufferISR( void )
{
char cIn;
BaseType_t xHigherPriorityTaskWoken;
// We have not woken a task at the start of the ISR.
xHigherPriorityTaskWoken = pdFALSE;
// Loop until the buffer is empty.
do
{
// Obtain a byte from the buffer.
cIn = portINPUT_BYTE( RX_REGISTER_ADDRESS );
// Post the byte.
xQueueSendFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWoken );
} while( portINPUT_BYTE( BUFFER_COUNT ) );
// Now the buffer is empty we can switch context if necessary.
if( xHigherPriorityTaskWoken )
{
// Actual macro used here is port specific.
portYIELD_FROM_ISR ();
}
}
Creates a new mutex type semaphore instance, and returns a handle by which the new mutex can be referenced. Internally, within the FreeRTOS implementation, mutex semaphores use a block of memory, in which the mutex structure is stored. If a mutex is created using xSemaphoreCreateMutex() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateMutex() function. (see https://www.FreeRTOS.org/a00111.html). If a mutex is created using xSemaphoreCreateMutexStatic() then the application writer must provided the memory. xSemaphoreCreateMutexStatic() therefore allows a mutex to be created without using any dynamic memory allocation. Mutexes created using this function can be accessed using the xSemaphoreTake() and xSemaphoreGive() macros. The xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros must not be used. This type of semaphore uses a priority inheritance mechanism so a task 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the semaphore it is no longer required. Mutex type semaphores cannot be used from within interrupt service routines. See xSemaphoreCreateBinary() for an alternative implementation that can be used for pure synchronisation (where one task or interrupt always 'gives' the semaphore and another always 'takes' the semaphore) and from within interrupt service routines. Example usage:
{c}
SemaphoreHandle_t xSemaphore;
void vATask( void * pvParameters )
{
// Semaphore cannot be used before a call to xSemaphoreCreateMutex().
// This is a macro so pass the variable in directly.
xSemaphore = xSemaphoreCreateMutex();
if( xSemaphore != NULL )
{
// The semaphore was created successfully.
// The semaphore can now be used.
}
}
@endcond Used with the uxTaskGetSystemState() function to return the state of each task in the system.
Macro to release a semaphore. The semaphore must have previously been created with a call to xSemaphoreCreateBinary() or xSemaphoreCreateCounting(). Mutex type semaphores (those created using a call to xSemaphoreCreateMutex()) must not be used with this macro. This macro can be used from an ISR. Example usage:
{c}
#define LONG_TIME 0xffff
#define TICKS_TO_WAIT 10
SemaphoreHandle_t xSemaphore = NULL;
// Repetitive task.
void vATask( void * pvParameters )
{
for( ;; )
{
// We want this task to run every 10 ticks of a timer. The semaphore
// was created before this task was started.
// Block waiting for the semaphore to become available.
if( xSemaphoreTake( xSemaphore, LONG_TIME ) == pdTRUE )
{
// It is time to execute.
// ...
// We have finished our task. Return to the top of the loop where
// we will block on the semaphore until it is time to execute
// again. Note when using the semaphore for synchronisation with an
// ISR in this manner there is no need to 'give' the semaphore back.
}
}
}
// Timer ISR
void vTimerISR( void * pvParameters )
{
static uint8_t ucLocalTickCount = 0;
static BaseType_t xHigherPriorityTaskWoken;
// A timer tick has occurred.
// ... Do other time functions.
// Is it time for vATask () to run?
xHigherPriorityTaskWoken = pdFALSE;
ucLocalTickCount++;
if( ucLocalTickCount >= TICKS_TO_WAIT )
{
// Unblock the task by releasing the semaphore.
xSemaphoreGiveFromISR( xSemaphore, &xHigherPriorityTaskWoken );
// Reset the count so we release the semaphore again in 10 ticks time.
ucLocalTickCount = 0;
}
if( xHigherPriorityTaskWoken != pdFALSE )
{
// We can force a context switch here. Context switching from an
// ISR uses port specific syntax. Check the demo task for your port
// to find the syntax required.
}
}
Macro to recursively release, or 'give', a mutex type semaphore. The mutex must have previously been created using a call to xSemaphoreCreateRecursiveMutex(); configUSE_RECURSIVE_MUTEXES must be set to 1 in FreeRTOSConfig.h for this macro to be available. This macro must not be used on mutexes created using xSemaphoreCreateMutex(). A mutex used recursively can be 'taken' repeatedly by the owner. The mutex doesn't become available again until the owner has called xSemaphoreGiveRecursive() for each successful 'take' request. For example, if a task successfully 'takes' the same mutex 5 times then the mutex will not be available to any other task until it has also 'given' the mutex back exactly five times. Example usage:
{c}
SemaphoreHandle_t xMutex = NULL;
// A task that creates a mutex.
void vATask( void * pvParameters )
{
// Create the mutex to guard a shared resource.
xMutex = xSemaphoreCreateRecursiveMutex();
}
// A task that uses the mutex.
void vAnotherTask( void * pvParameters )
{
// ... Do other things.
if( xMutex != NULL )
{
// See if we can obtain the mutex. If the mutex is not available
// wait 10 ticks to see if it becomes free.
if( xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 ) == pdTRUE )
{
// We were able to obtain the mutex and can now access the
// shared resource.
// ...
// For some reason due to the nature of the code further calls to
// xSemaphoreTakeRecursive() are made on the same mutex. In real
// code these would not be just sequential calls as this would make
// no sense. Instead the calls are likely to be buried inside
// a more complex call structure.
xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 );
xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 );
// The mutex has now been 'taken' three times, so will not be
// available to another task until it has also been given back
// three times. Again it is unlikely that real code would have
// these calls sequentially, it would be more likely that the calls
// to xSemaphoreGiveRecursive() would be called as a call stack
// unwound. This is just for demonstrative purposes.
xSemaphoreGiveRecursive( xMutex );
xSemaphoreGiveRecursive( xMutex );
xSemaphoreGiveRecursive( xMutex );
// Now the mutex can be taken by other tasks.
}
else
{
// We could not obtain the mutex and can therefore not access
// the shared resource safely.
}
}
}
Timer functionality is provided by a timer service/daemon task. Many of the public FreeRTOS timer API functions send commands to the timer service task through a queue called the timer command queue. The timer command queue is private to the kernel itself and is not directly accessible to application code. The length of the timer command queue is set by the configTIMER_QUEUE_LENGTH configuration constant. xTimerReset() re-starts a timer that was previously created using the xTimerCreate() API function. If the timer had already been started and was already in the active state, then xTimerReset() will cause the timer to re-evaluate its expiry time so that it is relative to when xTimerReset() was called. If the timer was in the dormant state then xTimerReset() has equivalent functionality to the xTimerStart() API function. Resetting a timer ensures the timer is in the active state. If the timer is not stopped, deleted, or reset in the mean time, the callback function associated with the timer will get called 'n' ticks after xTimerReset() was called, where 'n' is the timers defined period. It is valid to call xTimerReset() before the scheduler has been started, but when this is done the timer will not actually start until the scheduler is started, and the timers expiry time will be relative to when the scheduler is started, not relative to when xTimerReset() was called. The configUSE_TIMERS configuration constant must be set to 1 for xTimerReset() to be available. Example usage: @verbatim // When a key is pressed, an LCD back-light is switched on. If 5 seconds pass // without a key being pressed, then the LCD back-light is switched off. In // this case, the timer is a one-shot timer. TimerHandle_t xBacklightTimer = NULL; // The callback function assigned to the one-shot timer. In this case the // parameter is not used. void vBacklightTimerCallback( TimerHandle_t pxTimer ) { // The timer expired, therefore 5 seconds must have passed since a key // was pressed. Switch off the LCD back-light. vSetBacklightState( BACKLIGHT_OFF ); } // The key press event handler. void vKeyPressEventHandler( char cKey ) { // Ensure the LCD back-light is on, then reset the timer that is // responsible for turning the back-light off after 5 seconds of // key inactivity. Wait 10 ticks for the command to be successfully sent // if it cannot be sent immediately. vSetBacklightState( BACKLIGHT_ON ); if( xTimerReset( xBacklightTimer, 100 ) != pdPASS ) { // The reset command was not executed successfully. Take appropriate // action here. } // Perform the rest of the key processing here. } void main( void ) { int32_t x; // Create then start the one-shot timer that is responsible for turning // the back-light off if no keys are pressed within a 5 second period. xBacklightTimer = xTimerCreate( "BacklightTimer", // Just a text name, not used by the kernel. ( 5000 / portTICK_PERIOD_MS), // The timer period in ticks. pdFALSE, // The timer is a one-shot timer. 0, // The id is not used by the callback so can take any value. vBacklightTimerCallback // The callback function that switches the LCD back-light off. ); if( xBacklightTimer == NULL ) { // The timer was not created. } else { // Start the timer. No block time is specified, and even if one was // it would be ignored because the scheduler has not yet been // started. if( xTimerStart( xBacklightTimer, 0 ) != pdPASS ) { // The timer could not be set into the Active state. } } // ... // Create tasks here. // ... // Starting the scheduler will start the timer running as it has already // been set into the active state. vTaskStartScheduler(); // Should not reach here. for( ;; ); } @endverbatim
Macro to recursively obtain, or 'take', a mutex type semaphore. The mutex must have previously been created using a call to xSemaphoreCreateRecursiveMutex(); configUSE_RECURSIVE_MUTEXES must be set to 1 in FreeRTOSConfig.h for this macro to be available. This macro must not be used on mutexes created using xSemaphoreCreateMutex(). A mutex used recursively can be 'taken' repeatedly by the owner. The mutex doesn't become available again until the owner has called xSemaphoreGiveRecursive() for each successful 'take' request. For example, if a task successfully 'takes' the same mutex 5 times then the mutex will not be available to any other task until it has also 'given' the mutex back exactly five times. Example usage:
{c}
SemaphoreHandle_t xMutex = NULL;
// A task that creates a mutex.
void vATask( void * pvParameters )
{
// Create the mutex to guard a shared resource.
xMutex = xSemaphoreCreateRecursiveMutex();
}
// A task that uses the mutex.
void vAnotherTask( void * pvParameters )
{
// ... Do other things.
if( xMutex != NULL )
{
// See if we can obtain the mutex. If the mutex is not available
// wait 10 ticks to see if it becomes free.
if( xSemaphoreTakeRecursive( xSemaphore, ( TickType_t ) 10 ) == pdTRUE )
{
// We were able to obtain the mutex and can now access the
// shared resource.
// ...
// For some reason due to the nature of the code further calls to
// xSemaphoreTakeRecursive() are made on the same mutex. In real
// code these would not be just sequential calls as this would make
// no sense. Instead the calls are likely to be buried inside
// a more complex call structure.
xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 );
xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 );
// The mutex has now been 'taken' three times, so will not be
// available to another task until it has also been given back
// three times. Again it is unlikely that real code would have
// these calls sequentially, but instead buried in a more complex
// call structure. This is just for illustrative purposes.
xSemaphoreGiveRecursive( xMutex );
xSemaphoreGiveRecursive( xMutex );
xSemaphoreGiveRecursive( xMutex );
// Now the mutex can be taken by other tasks.
}
else
{
// We could not obtain the mutex and can therefore not access
// the shared resource safely.
}
}
}
Task Snapshot structure - Used with the uxTaskGetSnapshotAll() function to save memory snapshot of each task in the system. - We need this structure because TCB_t is defined (hidden) in tasks.c.
Creates a new recursive mutex type semaphore instance, and returns a handle by which the new recursive mutex can be referenced. Internally, within the FreeRTOS implementation, recursive mutexes use a block of memory, in which the mutex structure is stored. If a recursive mutex is created using xSemaphoreCreateRecursiveMutex() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateRecursiveMutex() function. (see https://www.FreeRTOS.org/a00111.html). If a recursive mutex is created using xSemaphoreCreateRecursiveMutexStatic() then the application writer must provide the memory that will get used by the mutex. xSemaphoreCreateRecursiveMutexStatic() therefore allows a recursive mutex to be created without using any dynamic memory allocation. Mutexes created using this macro can be accessed using the xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros. The xSemaphoreTake() and xSemaphoreGive() macros must not be used. A mutex used recursively can be 'taken' repeatedly by the owner. The mutex doesn't become available again until the owner has called xSemaphoreGiveRecursive() for each successful 'take' request. For example, if a task successfully 'takes' the same mutex 5 times then the mutex will not be available to any other task until it has also 'given' the mutex back exactly five times. This type of semaphore uses a priority inheritance mechanism so a task 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the semaphore it is no longer required. Mutex type semaphores cannot be used from within interrupt service routines. See xSemaphoreCreateBinary() for an alternative implementation that can be used for pure synchronisation (where one task or interrupt always 'gives' the semaphore and another always 'takes' the semaphore) and from within interrupt service routines. Example usage:
{c}
SemaphoreHandle_t xSemaphore;
void vATask( void * pvParameters )
{
// Semaphore cannot be used before a call to xSemaphoreCreateMutex().
// This is a macro so pass the variable in directly.
xSemaphore = xSemaphoreCreateRecursiveMutex();
if( xSemaphore != NULL )
{
// The semaphore was created successfully.
// The semaphore can now be used.
}
}
Timer functionality is provided by a timer service/daemon task. Many of the public FreeRTOS timer API functions send commands to the timer service task through a queue called the timer command queue. The timer command queue is private to the kernel itself and is not directly accessible to application code. The length of the timer command queue is set by the configTIMER_QUEUE_LENGTH configuration constant. xTimerDelete() deletes a timer that was previously created using the xTimerCreate() API function. The configUSE_TIMERS configuration constant must be set to 1 for xTimerDelete() to be available. Example usage: See the xTimerChangePeriod() API function example usage scenario.
Creates a new counting semaphore instance, and returns a handle by which the new counting semaphore can be referenced. In many usage scenarios it is faster and more memory efficient to use a direct to task notification in place of a counting semaphore! https://www.FreeRTOS.org/RTOS-task-notifications.html Internally, within the FreeRTOS implementation, counting semaphores use a block of memory, in which the counting semaphore structure is stored. If a counting semaphore is created using xSemaphoreCreateCounting() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateCounting() function. (see https://www.FreeRTOS.org/a00111.html). If a counting semaphore is created using xSemaphoreCreateCountingStatic() then the application writer can instead optionally provide the memory that will get used by the counting semaphore. xSemaphoreCreateCountingStatic() therefore allows a counting semaphore to be created without using any dynamic memory allocation. Counting semaphores are typically used for two things: 1) Counting events. In this usage scenario an event handler will 'give' a semaphore each time an event occurs (incrementing the semaphore count value), and a handler task will 'take' a semaphore each time it processes an event (decrementing the semaphore count value). The count value is therefore the difference between the number of events that have occurred and the number that have been processed. In this case it is desirable for the initial count value to be zero. 2) Resource management. In this usage scenario the count value indicates the number of resources available. To obtain control of a resource a task must first obtain a semaphore - decrementing the semaphore count value. When the count value reaches zero there are no free resources. When a task finishes with the resource it 'gives' the semaphore back - incrementing the semaphore count value. In this case it is desirable for the initial count value to be equal to the maximum count value, indicating that all resources are free. Example usage:
{c}
SemaphoreHandle_t xSemaphore;
void vATask( void * pvParameters )
{
SemaphoreHandle_t xSemaphore = NULL;
// Semaphore cannot be used before a call to xSemaphoreCreateCounting().
// The max value to which the semaphore can count should be 10, and the
// initial value assigned to the count should be 0.
xSemaphore = xSemaphoreCreateCounting( 10, 0 );
if( xSemaphore != NULL )
{
// The semaphore was created successfully.
// The semaphore can now be used.
}
}
Sends a direct to task notification to a particular index in the target task's notification array in a manner similar to giving a counting semaphore. See https://www.FreeRTOS.org/RTOS-task-notifications.html for more details. configUSE_TASK_NOTIFICATIONS must be undefined or defined as 1 for these macros to be available. Each task has a private array of "notification values" (or 'notifications'), each of which is a 32-bit unsigned integer (uint32_t). The constant configTASK_NOTIFICATION_ARRAY_ENTRIES sets the number of indexes in the array, and (for backward compatibility) defaults to 1 if left undefined. Prior to FreeRTOS V10.4.0 there was only one notification value per task. Events can be sent to a task using an intermediary object. Examples of such objects are queues, semaphores, mutexes and event groups. Task notifications are a method of sending an event directly to a task without the need for such an intermediary object. A notification sent to a task can optionally perform an action, such as update, overwrite or increment one of the task's notification values. In that way task notifications can be used to send data to a task, or be used as light weight and fast binary or counting semaphores. xTaskNotifyGiveIndexed() is a helper macro intended for use when task notifications are used as light weight and faster binary or counting semaphore equivalents. Actual FreeRTOS semaphores are given using the xSemaphoreGive() API function, the equivalent action that instead uses a task notification is xTaskNotifyGiveIndexed(). When task notifications are being used as a binary or counting semaphore equivalent then the task being notified should wait for the notification using the ulTaskNotifyTakeIndexed() API function rather than the xTaskNotifyWaitIndexed() API function. **NOTE** Each notification within the array operates independently - a task can only block on one notification within the array at a time and will not be unblocked by a notification sent to any other array index. Backward compatibility information: Prior to FreeRTOS V10.4.0 each task had a single "notification value", and all task notification API functions operated on that value. Replacing the single notification value with an array of notification values necessitated a new set of API functions that could address specific notifications within the array. xTaskNotifyGive() is the original API function, and remains backward compatible by always operating on the notification value at index 0 in the array. Calling xTaskNotifyGive() is equivalent to calling xTaskNotifyGiveIndexed() with the uxIndexToNotify parameter set to 0.
This is a macro that calls xQueueGenericSend(). Post an item to the back of a queue. The item is queued by copy, not by reference. This function must not be called from an interrupt service routine. See xQueueSendFromISR () for an alternative which may be used in an ISR. Example usage:
{c}
struct AMessage
{
char ucMessageID;
char ucData[ 20 ];
} xMessage;
uint32_t ulVar = 10UL;
void vATask( void *pvParameters )
{
QueueHandle_t xQueue1, xQueue2;
struct AMessage *pxMessage;
// Create a queue capable of containing 10 uint32_t values.
xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) );
// Create a queue capable of containing 10 pointers to AMessage structures.
// These should be passed by pointer as they contain a lot of data.
xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) );
// ...
if( xQueue1 != 0 )
{
// Send an uint32_t. Wait for 10 ticks for space to become
// available if necessary.
if( xQueueSendToBack( xQueue1, ( void * ) &ulVar, ( TickType_t ) 10 ) != pdPASS )
{
// Failed to post the message, even after 10 ticks.
}
}
if( xQueue2 != 0 )
{
// Send a pointer to a struct AMessage object. Don't block if the
// queue is already full.
pxMessage = & xMessage;
xQueueSendToBack( xQueue2, ( void * ) &pxMessage, ( TickType_t ) 0 );
}
// ... Rest of task code.
}
Task Snapshot iterator Used in xTaskGetNext(). Must be zero/null initialized on the first call.
Structure to save a task's previous priority This structure is meant to be used with prvTaskPriorityRaise() and prvTaskPriorityRestore().
If the semaphore is a counting semaphore then uxSemaphoreGetCount() returns its current count value. If the semaphore is a binary semaphore then uxSemaphoreGetCount() returns 1 if the semaphore is available, and 0 if the semaphore is not available.
Definitions returned by xTaskGetSchedulerState(). taskSCHEDULER_SUSPENDED is 0 to generate more optimal code when configASSERT() is defined as the constant
Defines the prototype to which timer callback functions must conform.
The total run time allocated to the task so far, as defined by the run time stats clock. See https://www.FreeRTOS.org/rtos-run-time-stats.html. Only valid when configGENERATE_RUN_TIME_STATS is defined as 1 in FreeRTOSConfig.h.
The task being queried is in the Suspended state, or is in the Blocked state with an infinite time out.
The handle of the task to which the rest of the information in the structure relates.
Macro to take a semaphore from an ISR. The semaphore must have previously been created with a call to xSemaphoreCreateBinary() or xSemaphoreCreateCounting(). Mutex type semaphores (those created using a call to xSemaphoreCreateMutex()) must not be used with this macro. This macro can be used from an ISR, however taking a semaphore from an ISR is not a common operation. It is likely to only be useful when taking a counting semaphore when an interrupt is obtaining an object from a resource pool (when the semaphore count indicates the number of resources available).
Timer functionality is provided by a timer service/daemon task. Many of the public FreeRTOS timer API functions send commands to the timer service task through a queue called the timer command queue. The timer command queue is private to the kernel itself and is not directly accessible to application code. The length of the timer command queue is set by the configTIMER_QUEUE_LENGTH configuration constant. xTimerStart() starts a timer that was previously created using the xTimerCreate() API function. If the timer had already been started and was already in the active state, then xTimerStart() has equivalent functionality to the xTimerReset() API function. Starting a timer ensures the timer is in the active state. If the timer is not stopped, deleted, or reset in the mean time, the callback function associated with the timer will get called 'n' ticks after xTimerStart() was called, where 'n' is the timers defined period. It is valid to call xTimerStart() before the scheduler has been started, but when this is done the timer will not actually start until the scheduler is started, and the timers expiry time will be relative to when the scheduler is started, not relative to when xTimerStart() was called. The configUSE_TIMERS configuration constant must be set to 1 for xTimerStart() to be available. Example usage: See the xTimerCreate() API function example usage scenario.
A pointer to the task's name. This value will be invalid if the task was deleted since the structure was populated!
Timer functionality is provided by a timer service/daemon task. Many of the public FreeRTOS timer API functions send commands to the timer service task through a queue called the timer command queue. The timer command queue is private to the kernel itself and is not directly accessible to application code. The length of the timer command queue is set by the configTIMER_QUEUE_LENGTH configuration constant. xTimerChangePeriod() changes the period of a timer that was previously created using the xTimerCreate() API function. xTimerChangePeriod() can be called to change the period of an active or dormant state timer. The configUSE_TIMERS configuration constant must be set to 1 for xTimerChangePeriod() to be available. Example usage: @verbatim // This function assumes xTimer has already been created. If the timer // referenced by xTimer is already active when it is called, then the timer // is deleted. If the timer referenced by xTimer is not active when it is // called, then the period of the timer is set to 500ms and the timer is // started. void vAFunction( TimerHandle_t xTimer ) { if( xTimerIsTimerActive( xTimer ) != pdFALSE ) // or more simply and equivalently "if( xTimerIsTimerActive( xTimer ) )" { // xTimer is already active - delete it. xTimerDelete( xTimer ); } else { // xTimer is not active, change its period to 500ms. This will also // cause the timer to start. Block for a maximum of 100 ticks if the // change period command cannot immediately be sent to the timer // command queue. if( xTimerChangePeriod( xTimer, 500 / portTICK_PERIOD_MS, 100 ) == pdPASS ) { // The command was successfully sent. } else { // The command could not be sent, even after waiting for 100 ticks // to pass. Take appropriate action here. } } } @endverbatim
Defines the prototype to which functions used with the xTimerPendFunctionCallFromISR() function must conform.
Set the task's notification value to a specific value even if the previous value has not yet been read by the task.
Prototype of local storage pointer deletion callback.
Used by FreeRTOS functions to call the correct version of critical section API
Align stack pointer in a downward growing stack This macro is used to round a stack pointer downwards to the nearest n-byte boundary, where n is a power of 2. This macro is generally used when allocating aligned areas on a downward growing stack.
Creates a new queue instance, and returns a handle by which the new queue can be referenced. Internally, within the FreeRTOS implementation, queues use two blocks of memory. The first block is used to hold the queue's data structures. The second block is used to hold items placed into the queue. If a queue is created using xQueueCreate() then both blocks of memory are automatically dynamically allocated inside the xQueueCreate() function. (see https://www.FreeRTOS.org/a00111.html). If a queue is created using xQueueCreateStatic() then the application writer must provide the memory that will get used by the queue. xQueueCreateStatic() therefore allows a queue to be created without using any dynamic memory allocation. https://www.FreeRTOS.org/Embedded-RTOS-Queues.html Example usage:
{c}
struct AMessage
{
char ucMessageID;
char ucData[ 20 ];
};
#define QUEUE_LENGTH 10
#define ITEM_SIZE sizeof( uint32_t )
// xQueueBuffer will hold the queue structure.
StaticQueue_t xQueueBuffer;
// ucQueueStorage will hold the items posted to the queue. Must be at least
// [(queue length) * ( queue item size)] bytes long.
uint8_t ucQueueStorage[ QUEUE_LENGTH * ITEM_SIZE ];
void vATask( void *pvParameters )
{
QueueHandle_t xQueue1;
// Create a queue capable of containing 10 uint32_t values.
xQueue1 = xQueueCreate( QUEUE_LENGTH, // The number of items the queue can hold.
ITEM_SIZE // The size of each item in the queue
&( ucQueueStorage[ 0 ] ), // The buffer that will hold the items in the queue.
&xQueueBuffer ); // The buffer that will hold the queue structure.
// The queue is guaranteed to be created successfully as no dynamic memory
// allocation is used. Therefore xQueue1 is now a handle to a valid queue.
// ... Rest of task code.
}
This is a macro that calls xQueueGenericSendFromISR(). Post an item to the back of a queue. It is safe to use this macro from within an interrupt service routine. Items are queued by copy not reference so it is preferable to only queue small items, especially when called from an ISR. In most cases it would be preferable to store a pointer to the item being queued. Example usage for buffered IO (where the ISR can obtain more than one value per call):
{c}
void vBufferISR( void )
{
char cIn;
BaseType_t xHigherPriorityTaskWoken;
// We have not woken a task at the start of the ISR.
xHigherPriorityTaskWoken = pdFALSE;
// Loop until the buffer is empty.
do
{
// Obtain a byte from the buffer.
cIn = portINPUT_BYTE( RX_REGISTER_ADDRESS );
// Post the byte.
xQueueSendToBackFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWoken );
} while( portINPUT_BYTE( BUFFER_COUNT ) );
// Now the buffer is empty we can switch context if necessary.
if( xHigherPriorityTaskWoken )
{
taskYIELD ();
}
}
Creates a new mutex type semaphore instance, and returns a handle by which the new mutex can be referenced. Internally, within the FreeRTOS implementation, mutex semaphores use a block of memory, in which the mutex structure is stored. If a mutex is created using xSemaphoreCreateMutex() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateMutex() function. (see https://www.FreeRTOS.org/a00111.html). If a mutex is created using xSemaphoreCreateMutexStatic() then the application writer must provided the memory. xSemaphoreCreateMutexStatic() therefore allows a mutex to be created without using any dynamic memory allocation. Mutexes created using this function can be accessed using the xSemaphoreTake() and xSemaphoreGive() macros. The xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros must not be used. This type of semaphore uses a priority inheritance mechanism so a task 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the semaphore it is no longer required. Mutex type semaphores cannot be used from within interrupt service routines. See xSemaphoreCreateBinary() for an alternative implementation that can be used for pure synchronisation (where one task or interrupt always 'gives' the semaphore and another always 'takes' the semaphore) and from within interrupt service routines. Example usage:
{c}
SemaphoreHandle_t xSemaphore;
StaticSemaphore_t xMutexBuffer;
void vATask( void * pvParameters )
{
// A mutex cannot be used before it has been created. xMutexBuffer is
// into xSemaphoreCreateMutexStatic() so no dynamic memory allocation is
// attempted.
xSemaphore = xSemaphoreCreateMutexStatic( &xMutexBuffer );
// As no dynamic memory allocation was performed, xSemaphore cannot be NULL,
// so there is no need to check it.
}
Creates a new counting semaphore instance, and returns a handle by which the new counting semaphore can be referenced. In many usage scenarios it is faster and more memory efficient to use a direct to task notification in place of a counting semaphore! https://www.FreeRTOS.org/RTOS-task-notifications.html Internally, within the FreeRTOS implementation, counting semaphores use a block of memory, in which the counting semaphore structure is stored. If a counting semaphore is created using xSemaphoreCreateCounting() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateCounting() function. (see https://www.FreeRTOS.org/a00111.html). If a counting semaphore is created using xSemaphoreCreateCountingStatic() then the application writer must provide the memory. xSemaphoreCreateCountingStatic() therefore allows a counting semaphore to be created without using any dynamic memory allocation. Counting semaphores are typically used for two things: 1) Counting events. In this usage scenario an event handler will 'give' a semaphore each time an event occurs (incrementing the semaphore count value), and a handler task will 'take' a semaphore each time it processes an event (decrementing the semaphore count value). The count value is therefore the difference between the number of events that have occurred and the number that have been processed. In this case it is desirable for the initial count value to be zero. 2) Resource management. In this usage scenario the count value indicates the number of resources available. To obtain control of a resource a task must first obtain a semaphore - decrementing the semaphore count value. When the count value reaches zero there are no free resources. When a task finishes with the resource it 'gives' the semaphore back - incrementing the semaphore count value. In this case it is desirable for the initial count value to be equal to the maximum count value, indicating that all resources are free. Example usage:
{c}
SemaphoreHandle_t xSemaphore;
StaticSemaphore_t xSemaphoreBuffer;
void vATask( void * pvParameters )
{
SemaphoreHandle_t xSemaphore = NULL;
// Counting semaphore cannot be used before they have been created. Create
// a counting semaphore using xSemaphoreCreateCountingStatic(). The max
// value to which the semaphore can count is 10, and the initial value
// assigned to the count will be 0. The address of xSemaphoreBuffer is
// passed in and will be used to hold the semaphore structure, so no dynamic
// memory allocation will be used.
xSemaphore = xSemaphoreCreateCounting( 10, 0, &xSemaphoreBuffer );
// No memory allocation was attempted so xSemaphore cannot be NULL, so there
// is no need to check its value.
}
If xMutex is indeed a mutex type semaphore, return the current mutex holder. If xMutex is not a mutex type semaphore, or the mutex is available (not held by a task), return NULL. Note: This is a good way of determining if the calling task is the mutex holder, but not a good way of determining the identity of the mutex holder as the holder may change between the function exiting and the returned value being tested.
The minimum amount of stack space that has remained for the task since the task was created. The closer this value is to zero the closer the task has come to overflowing its stack.
A task has been made ready or a context switch pended since portSUPPRESS_TICKS_AND_SLEEP() was called - abort entering a sleep mode.
When passed for 'timeout_cycles', spin forever if necessary. [refactor-todo] check if this is still required
- Only applies to current core - These cannot be nested. They should be used with a lot of care and cannot be called from interrupt level.
Creates a new binary semaphore instance, and returns a handle by which the new semaphore can be referenced. NOTE: In many usage scenarios it is faster and more memory efficient to use a direct to task notification in place of a binary semaphore! https://www.FreeRTOS.org/RTOS-task-notifications.html Internally, within the FreeRTOS implementation, binary semaphores use a block of memory, in which the semaphore structure is stored. If a binary semaphore is created using xSemaphoreCreateBinary() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateBinary() function. (see https://www.FreeRTOS.org/a00111.html). If a binary semaphore is created using xSemaphoreCreateBinaryStatic() then the application writer must provide the memory. xSemaphoreCreateBinaryStatic() therefore allows a binary semaphore to be created without using any dynamic memory allocation. This type of semaphore can be used for pure synchronisation between tasks or between an interrupt and a task. The semaphore need not be given back once obtained, so one task/interrupt can continuously 'give' the semaphore while another continuously 'takes' the semaphore. For this reason this type of semaphore does not use a priority inheritance mechanism. For an alternative that does use priority inheritance see xSemaphoreCreateMutex(). Example usage:
{c}
SemaphoreHandle_t xSemaphore = NULL;
StaticSemaphore_t xSemaphoreBuffer;
void vATask( void * pvParameters )
{
// Semaphore cannot be used before a call to xSemaphoreCreateBinary().
// The semaphore's data structures will be placed in the xSemaphoreBuffer
// variable, the address of which is passed into the function. The
// function's parameter is not NULL, so the function will not attempt any
// dynamic memory allocation, and therefore the function will not return
// return NULL.
xSemaphore = xSemaphoreCreateBinary( &xSemaphoreBuffer );
// Rest of task code goes here.
}
Returns the current value of the bits in an event group. This function cannot be used from an interrupt.
Set the task's notification value if the previous value has been read by the task.
The priority at which the task was running (may be inherited) when the structure was populated.
Retrieve pointers to a statically created queue's data structure buffer and storage area buffer. These are the same buffers that are supplied at the time of creation.
Creates a new recursive mutex type semaphore instance, and returns a handle by which the new recursive mutex can be referenced. Internally, within the FreeRTOS implementation, recursive mutexes use a block of memory, in which the mutex structure is stored. If a recursive mutex is created using xSemaphoreCreateRecursiveMutex() then the required memory is automatically dynamically allocated inside the xSemaphoreCreateRecursiveMutex() function. (see https://www.FreeRTOS.org/a00111.html). If a recursive mutex is created using xSemaphoreCreateRecursiveMutexStatic() then the application writer must provide the memory that will get used by the mutex. xSemaphoreCreateRecursiveMutexStatic() therefore allows a recursive mutex to be created without using any dynamic memory allocation. Mutexes created using this macro can be accessed using the xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros. The xSemaphoreTake() and xSemaphoreGive() macros must not be used. A mutex used recursively can be 'taken' repeatedly by the owner. The mutex doesn't become available again until the owner has called xSemaphoreGiveRecursive() for each successful 'take' request. For example, if a task successfully 'takes' the same mutex 5 times then the mutex will not be available to any other task until it has also 'given' the mutex back exactly five times. This type of semaphore uses a priority inheritance mechanism so a task 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the semaphore it is no longer required. Mutex type semaphores cannot be used from within interrupt service routines. See xSemaphoreCreateBinary() for an alternative implementation that can be used for pure synchronisation (where one task or interrupt always 'gives' the semaphore and another always 'takes' the semaphore) and from within interrupt service routines. Example usage:
{c}
SemaphoreHandle_t xSemaphore;
StaticSemaphore_t xMutexBuffer;
void vATask( void * pvParameters )
{
// A recursive semaphore cannot be used before it is created. Here a
// recursive mutex is created using xSemaphoreCreateRecursiveMutexStatic().
// The address of xMutexBuffer is passed into the function, and will hold
// the mutexes data structures - so no dynamic memory allocation will be
// attempted.
xSemaphore = xSemaphoreCreateRecursiveMutexStatic( &xMutexBuffer );
// As no dynamic memory allocation was performed, xSemaphore cannot be NULL,
// so there is no need to check it.
}
A version of xQueueOverwrite() that can be used in an interrupt service routine (ISR). Only for use with queues that can hold a single item - so the queue is either empty or full. Post an item on a queue. If the queue is already full then overwrite the value held in the queue. The item is queued by copy, not by reference. Example usage:
{c}
QueueHandle_t xQueue;
void vFunction( void *pvParameters )
{
// Create a queue to hold one uint32_t value. It is strongly
// recommended *not* to use xQueueOverwriteFromISR() on queues that can
// contain more than one value, and doing so will trigger an assertion
// if configASSERT() is defined.
xQueue = xQueueCreate( 1, sizeof( uint32_t ) );
}
void vAnInterruptHandler( void )
{
// xHigherPriorityTaskWoken must be set to pdFALSE before it is used.
BaseType_t xHigherPriorityTaskWoken = pdFALSE;
uint32_t ulVarToSend, ulValReceived;
// Write the value 10 to the queue using xQueueOverwriteFromISR().
ulVarToSend = 10;
xQueueOverwriteFromISR( xQueue, &ulVarToSend, &xHigherPriorityTaskWoken );
// The queue is full, but calling xQueueOverwriteFromISR() again will still
// pass because the value held in the queue will be overwritten with the
// new value.
ulVarToSend = 100;
xQueueOverwriteFromISR( xQueue, &ulVarToSend, &xHigherPriorityTaskWoken );
// Reading from the queue will now return 100.
// ...
if( xHigherPrioritytaskWoken == pdTRUE )
{
// Writing to the queue caused a task to unblock and the unblocked task
// has a priority higher than or equal to the priority of the currently
// executing task (the task this interrupt interrupted). Perform a context
// switch so this interrupt returns directly to the unblocked task.
portYIELD_FROM_ISR(); // or portEND_SWITCHING_ISR() depending on the port.
}
}
The priority to which the task will return if the task's current priority has been inherited to avoid unbounded priority inversion when obtaining a mutex. Only valid if configUSE_MUTEXES is defined as 1 in FreeRTOSConfig.h.
Enter a sleep mode that will not last any longer than the expected idle time.
No tasks are waiting for a timeout so it is safe to enter a sleep mode that can only be exited by an external interrupt.
Retrieve pointer to a statically created binary semaphore, counting semaphore, or mutex semaphore's data structure buffer. This is the same buffer that is supplied at the time of creation.
Creates a new stream buffer using statically allocated memory. See xStreamBufferCreate() for a version that uses dynamically allocated memory. configSUPPORT_STATIC_ALLOCATION must be set to 1 in FreeRTOSConfig.h for xStreamBufferCreateStatic() to be available. Example use:
{c}
// Used to dimension the array used to hold the streams. The available space
// will actually be one less than this, so 999.
#define STORAGE_SIZE_BYTES 1000
// Defines the memory that will actually hold the streams within the stream
// buffer.
static uint8_t ucStorageBuffer[ STORAGE_SIZE_BYTES ];
// The variable used to hold the stream buffer structure.
StaticStreamBuffer_t xStreamBufferStruct;
void MyFunction( void )
{
StreamBufferHandle_t xStreamBuffer;
const size_t xTriggerLevel = 1;
xStreamBuffer = xStreamBufferCreateStatic( sizeof( ucStorageBuffer ),
xTriggerLevel,
ucStorageBuffer,
&xStreamBufferStruct );
// As neither the pucStreamBufferStorageArea or pxStaticStreamBuffer
// parameters were NULL, xStreamBuffer will not be NULL, and can be used to
// reference the created stream buffer in other stream buffer API calls.
// Other code that uses the stream buffer can go here.
}
Creates a new message buffer using statically allocated memory. See xMessageBufferCreate() for a version that uses dynamically allocated memory. Example use:
{c}
// Used to dimension the array used to hold the messages. The available space
// will actually be one less than this, so 999.
#define STORAGE_SIZE_BYTES 1000
// Defines the memory that will actually hold the messages within the message
// buffer.
static uint8_t ucStorageBuffer[ STORAGE_SIZE_BYTES ];
// The variable used to hold the message buffer structure.
StaticMessageBuffer_t xMessageBufferStruct;
void MyFunction( void )
{
MessageBufferHandle_t xMessageBuffer;
xMessageBuffer = xMessageBufferCreateStatic( sizeof( ucStorageBuffer ),
ucStorageBuffer,
&xMessageBufferStruct );
// As neither the pucMessageBufferStorageArea or pxStaticMessageBuffer
// parameters were NULL, xMessageBuffer will not be NULL, and can be used to
// reference the created message buffer in other message buffer API calls.
// Other code that uses the message buffer can go here.
}
Retrieve pointers to a statically created message buffer's data structure buffer and storage area buffer. These are the same buffers that are supplied at the time of creation.
Deletes a message buffer that was previously created using a call to xMessageBufferCreate() or xMessageBufferCreateStatic(). If the message buffer was created using dynamic memory (that is, by xMessageBufferCreate()), then the allocated memory is freed. A message buffer handle must not be used after the message buffer has been deleted.
Points to the end of the stack. pxTopOfStack < pxEndOfStack, stack grows hi2lo pxTopOfStack > pxEndOfStack, stack grows lo2hi
HOOKS TO DYNAMICALLY INSTALL INTERRUPT AND EXCEPTION HANDLERS PER LEVEL. This Xtensa RTOS port provides hooks for dynamically installing exception and interrupt handlers to facilitate automated testing where each test case can install its own handler for user exceptions and each interrupt priority (level). This consists of an array of function pointers indexed by interrupt priority, with index 0 being the user exception handler hook. Each entry in the array is initially 0, and may be replaced by a function pointer of type XT_INTEXC_HOOK. A handler may be uninstalled by installing 0. The handler for low and medium priority obeys ABI conventions so may be coded in C. For the exception handler, the cause is the contents of the EXCCAUSE reg, and the result is -1 if handled, else the cause (still needs handling). For interrupt handlers, the cause is a mask of pending enabled interrupts at that level, and the result is the same mask with the bits for the handled interrupts cleared (those not cleared still need handling). This allows a test case to either pre-handle or override the default handling for the exception or interrupt level (see xtensa_vectors.S). High priority handlers (including NMI) must be coded in assembly, are always called by 'call0' regardless of ABI, must preserve all registers except a0, and must not use or modify the interrupted stack. The hook argument 'cause' is not passed and the result is ignored, so as not to burden the caller with saving and restoring a2 (it assumes only one interrupt per level - see the discussion in high priority interrupts in xtensa_vectors.S). The handler therefore should be coded to prototype 'void h(void)' even though it plugs into an array of handlers of prototype 'unsigned h(unsigned)'. To enable interrupt/exception hooks, compile the RTOS with '-DXT_INTEXC_HOOKS'.
Post an item to the front of a queue. The item is queued by copy, not by reference. This function must not be called from an interrupt service routine. See xQueueSendFromISR () for an alternative which may be used in an ISR. Example usage:
{c}
struct AMessage
{
char ucMessageID;
char ucData[ 20 ];
} xMessage;
uint32_t ulVar = 10UL;
void vATask( void *pvParameters )
{
QueueHandle_t xQueue1, xQueue2;
struct AMessage *pxMessage;
// Create a queue capable of containing 10 uint32_t values.
xQueue1 = xQueueCreate( 10, sizeof( uint32_t ) );
// Create a queue capable of containing 10 pointers to AMessage structures.
// These should be passed by pointer as they contain a lot of data.
xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) );
// ...
if( xQueue1 != 0 )
{
// Send an uint32_t. Wait for 10 ticks for space to become
// available if necessary.
if( xQueueSendToFront( xQueue1, ( void * ) &ulVar, ( TickType_t ) 10 ) != pdPASS )
{
// Failed to post the message, even after 10 ticks.
}
}
if( xQueue2 != 0 )
{
// Send a pointer to a struct AMessage object. Don't block if the
// queue is already full.
pxMessage = & xMessage;
xQueueSendToFront( xQueue2, ( void * ) &pxMessage, ( TickType_t ) 0 );
}
// ... Rest of task code.
}
A version of xTimerStart() that can be called from an interrupt service routine. Example usage: @verbatim // This scenario assumes xBacklightTimer has already been created. When a // key is pressed, an LCD back-light is switched on. If 5 seconds pass // without a key being pressed, then the LCD back-light is switched off. In // this case, the timer is a one-shot timer, and unlike the example given for // the xTimerReset() function, the key press event handler is an interrupt // service routine. // The callback function assigned to the one-shot timer. In this case the // parameter is not used. void vBacklightTimerCallback( TimerHandle_t pxTimer ) { // The timer expired, therefore 5 seconds must have passed since a key // was pressed. Switch off the LCD back-light. vSetBacklightState( BACKLIGHT_OFF ); } // The key press interrupt service routine. void vKeyPressEventInterruptHandler( void ) { BaseType_t xHigherPriorityTaskWoken = pdFALSE; // Ensure the LCD back-light is on, then restart the timer that is // responsible for turning the back-light off after 5 seconds of // key inactivity. This is an interrupt service routine so can only // call FreeRTOS API functions that end in "FromISR". vSetBacklightState( BACKLIGHT_ON ); // xTimerStartFromISR() or xTimerResetFromISR() could be called here // as both cause the timer to re-calculate its expiry time. // xHigherPriorityTaskWoken was initialised to pdFALSE when it was // declared (in this function). if( xTimerStartFromISR( xBacklightTimer, &xHigherPriorityTaskWoken ) != pdPASS ) { // The start command was not executed successfully. Take appropriate // action here. } // Perform the rest of the key processing here. // If xHigherPriorityTaskWoken equals pdTRUE, then a context switch // should be performed. The syntax required to perform a context switch // from inside an ISR varies from port to port, and from compiler to // compiler. Inspect the demos for the port you are using to find the // actual syntax required. if( xHigherPriorityTaskWoken != pdFALSE ) { // Call the interrupt safe yield function here (actual function // depends on the FreeRTOS port being used). } } @endverbatim
Defines the prototype to which the application task hook function must conform.
Try to acquire the spinlock a single time only. [refactor-todo] check if this is still required
See https://www.FreeRTOS.org/RTOS-task-notifications.html for details. xTaskNotifyAndQueryIndexed() performs the same operation as xTaskNotifyIndexed() with the addition that it also returns the subject task's prior notification value (the notification value at the time the function is called rather than when the function returns) in the additional pulPreviousNotifyValue parameter. xTaskNotifyAndQuery() performs the same operation as xTaskNotify() with the addition that it also returns the subject task's prior notification value (the notification value as it was at the time the function is called, rather than when the function returns) in the additional pulPreviousNotifyValue parameter.
See https://www.FreeRTOS.org/RTOS-task-notifications.html for details. xTaskNotifyAndQueryIndexedFromISR() performs the same operation as xTaskNotifyIndexedFromISR() with the addition that it also returns the subject task's prior notification value (the notification value at the time the function is called rather than at the time the function returns) in the additional pulPreviousNotifyValue parameter. xTaskNotifyAndQueryFromISR() performs the same operation as xTaskNotifyFromISR() with the addition that it also returns the subject task's prior notification value (the notification value at the time the function is called rather than at the time the function returns) in the additional pulPreviousNotifyValue parameter.
Only for use with queues that have a length of one - so the queue is either empty or full. Post an item on a queue. If the queue is already full then overwrite the value held in the queue. The item is queued by copy, not by reference. This function must not be called from an interrupt service routine. See xQueueOverwriteFromISR () for an alternative which may be used in an ISR. Example usage:
{c}
void vFunction( void *pvParameters )
{
QueueHandle_t xQueue;
uint32_t ulVarToSend, ulValReceived;
// Create a queue to hold one uint32_t value. It is strongly
// recommended *not* to use xQueueOverwrite() on queues that can
// contain more than one value, and doing so will trigger an assertion
// if configASSERT() is defined.
xQueue = xQueueCreate( 1, sizeof( uint32_t ) );
// Write the value 10 to the queue using xQueueOverwrite().
ulVarToSend = 10;
xQueueOverwrite( xQueue, &ulVarToSend );
// Peeking the queue should now return 10, but leave the value 10 in
// the queue. A block time of zero is used as it is known that the
// queue holds a value.
ulValReceived = 0;
xQueuePeek( xQueue, &ulValReceived, 0 );
if( ulValReceived != 10 )
{
// Error unless the item was removed by a different task.
}
// The queue is still full. Use xQueueOverwrite() to overwrite the
// value held in the queue with 100.
ulVarToSend = 100;
xQueueOverwrite( xQueue, &ulVarToSend );
// This time read from the queue, leaving the queue empty once more.
// A block time of 0 is used again.
xQueueReceive( xQueue, &ulValReceived, 0 );
// The value read should be the last value written, even though the
// queue was already full when the value was written.
if( ulValReceived != 100 )
{
// Error!
}
// ...
}
This is a macro that calls xQueueGenericSendFromISR(). Post an item to the front of a queue. It is safe to use this macro from within an interrupt service routine. Items are queued by copy not reference so it is preferable to only queue small items, especially when called from an ISR. In most cases it would be preferable to store a pointer to the item being queued. Example usage for buffered IO (where the ISR can obtain more than one value per call):
{c}
void vBufferISR( void )
{
char cIn;
BaseType_t xHigherPriorityTaskWoken;
// We have not woken a task at the start of the ISR.
xHigherPriorityTaskWoken = pdFALSE;
// Loop until the buffer is empty.
do
{
// Obtain a byte from the buffer.
cIn = portINPUT_BYTE( RX_REGISTER_ADDRESS );
// Post the byte.
xQueueSendToFrontFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWoken );
} while( portINPUT_BYTE( BUFFER_COUNT ) );
// Now the buffer is empty we can switch context if necessary.
if( xHigherPriorityTaskWoken )
{
taskYIELD ();
}
}
In many usage scenarios it is faster and more memory efficient to use a direct to task notification in place of a binary semaphore! https://www.FreeRTOS.org/RTOS-task-notifications.html This old vSemaphoreCreateBinary() macro is now deprecated in favour of the xSemaphoreCreateBinary() function. Note that binary semaphores created using the vSemaphoreCreateBinary() macro are created in a state such that the first call to 'take' the semaphore would pass, whereas binary semaphores created using xSemaphoreCreateBinary() are created in a state such that the the semaphore must first be 'given' before it can be 'taken'. Macro that implements a semaphore by using the existing queue mechanism. The queue length is 1 as this is a binary semaphore. The data size is 0 as we don't want to actually store any data - we just want to know if the queue is empty or full. This type of semaphore can be used for pure synchronisation between tasks or between an interrupt and a task. The semaphore need not be given back once obtained, so one task/interrupt can continuously 'give' the semaphore while another continuously 'takes' the semaphore. For this reason this type of semaphore does not use a priority inheritance mechanism. For an alternative that does use priority inheritance see xSemaphoreCreateMutex(). Example usage:
{c}
SemaphoreHandle_t xSemaphore = NULL;
void vATask( void * pvParameters )
{
// Semaphore cannot be used before a call to vSemaphoreCreateBinary ().
// This is a macro so pass the variable in directly.
vSemaphoreCreateBinary( xSemaphore );
if( xSemaphore != NULL )
{
// The semaphore was created successfully.
// The semaphore can now be used.
}
}
If xMutex is indeed a mutex type semaphore, return the current mutex holder. If xMutex is not a mutex type semaphore, or the mutex is available (not held by a task), return NULL.
semphr.h
{c}
UBaseType_t uxSemaphoreGetCountFromISR( SemaphoreHandle_t xSemaphore );
If the semaphore is a counting semaphore then uxSemaphoreGetCountFromISR() returns its current count value. If the semaphore is a binary semaphore then uxSemaphoreGetCountFromISR() returns 1 if the semaphore is available, and 0 if the semaphore is not available. Creates a new stream buffer using dynamically allocated memory. See xStreamBufferCreateStatic() for a version that uses statically allocated memory (memory that is allocated at compile time). configSUPPORT_DYNAMIC_ALLOCATION must be set to 1 or left undefined in FreeRTOSConfig.h for xStreamBufferCreate() to be available. Example use:
{c}
void vAFunction( void )
{
StreamBufferHandle_t xStreamBuffer;
const size_t xStreamBufferSizeBytes = 100, xTriggerLevel = 10;
// Create a stream buffer that can hold 100 bytes. The memory used to hold
// both the stream buffer structure and the data in the stream buffer is
// allocated dynamically.
xStreamBuffer = xStreamBufferCreate( xStreamBufferSizeBytes, xTriggerLevel );
if( xStreamBuffer == NULL )
{
// There was not enough heap memory space available to create the
// stream buffer.
}
else
{
// The stream buffer was created successfully and can now be used.
}
}
Creates a new message buffer using dynamically allocated memory. See xMessageBufferCreateStatic() for a version that uses statically allocated memory (memory that is allocated at compile time). configSUPPORT_DYNAMIC_ALLOCATION must be set to 1 or left undefined in FreeRTOSConfig.h for xMessageBufferCreate() to be available. Example use:
{c}
void vAFunction( void )
{
MessageBufferHandle_t xMessageBuffer;
const size_t xMessageBufferSizeBytes = 100;
// Create a message buffer that can hold 100 bytes. The memory used to hold
// both the message buffer structure and the messages themselves is allocated
// dynamically. Each message added to the buffer consumes an additional 4
// bytes which are used to hold the length of the message.
xMessageBuffer = xMessageBufferCreate( xMessageBufferSizeBytes );
if( xMessageBuffer == NULL )
{
// There was not enough heap memory space available to create the
// message buffer.
}
else
{
// The message buffer was created successfully and can now be used.
}
Sends a discrete message to the message buffer. The message can be any length that fits within the buffer's free space, and is copied into the buffer. ***NOTE***: Uniquely among FreeRTOS objects, the stream buffer implementation (so also the message buffer implementation, as message buffers are built on top of stream buffers) assumes there is only one task or interrupt that will write to the buffer (the writer), and only one task or interrupt that will read from the buffer (the reader). It is safe for the writer and reader to be different tasks or interrupts, but, unlike other FreeRTOS objects, it is not safe to have multiple different writers or multiple different readers. If there are to be multiple different writers then the application writer must place each call to a writing API function (such as xMessageBufferSend()) inside a critical section and set the send block time to 0. Likewise, if there are to be multiple different readers then the application writer must place each call to a reading API function (such as xMessageBufferRead()) inside a critical section and set the receive block time to 0. Use xMessageBufferSend() to write to a message buffer from a task. Use xMessageBufferSendFromISR() to write to a message buffer from an interrupt service routine (ISR). Example use:
{c}
void vAFunction( MessageBufferHandle_t xMessageBuffer )
{
size_t xBytesSent;
uint8_t ucArrayToSend[] = { 0, 1, 2, 3 };
char *pcStringToSend = "String to send";
const TickType_t x100ms = pdMS_TO_TICKS( 100 );
// Send an array to the message buffer, blocking for a maximum of 100ms to
// wait for enough space to be available in the message buffer.
xBytesSent = xMessageBufferSend( xMessageBuffer, ( void * ) ucArrayToSend, sizeof( ucArrayToSend ), x100ms );
if( xBytesSent != sizeof( ucArrayToSend ) )
{
// The call to xMessageBufferSend() times out before there was enough
// space in the buffer for the data to be written.
}
// Send the string to the message buffer. Return immediately if there is
// not enough space in the buffer.
xBytesSent = xMessageBufferSend( xMessageBuffer, ( void * ) pcStringToSend, strlen( pcStringToSend ), 0 );
if( xBytesSent != strlen( pcStringToSend ) )
{
// The string could not be added to the message buffer because there was
// not enough free space in the buffer.
}
}
Interrupt safe version of the API function that sends a discrete message to the message buffer. The message can be any length that fits within the buffer's free space, and is copied into the buffer. ***NOTE***: Uniquely among FreeRTOS objects, the stream buffer implementation (so also the message buffer implementation, as message buffers are built on top of stream buffers) assumes there is only one task or interrupt that will write to the buffer (the writer), and only one task or interrupt that will read from the buffer (the reader). It is safe for the writer and reader to be different tasks or interrupts, but, unlike other FreeRTOS objects, it is not safe to have multiple different writers or multiple different readers. If there are to be multiple different writers then the application writer must place each call to a writing API function (such as xMessageBufferSend()) inside a critical section and set the send block time to 0. Likewise, if there are to be multiple different readers then the application writer must place each call to a reading API function (such as xMessageBufferRead()) inside a critical section and set the receive block time to 0. Use xMessageBufferSend() to write to a message buffer from a task. Use xMessageBufferSendFromISR() to write to a message buffer from an interrupt service routine (ISR). Example use:
{c}
// A message buffer that has already been created.
MessageBufferHandle_t xMessageBuffer;
void vAnInterruptServiceRoutine( void )
{
size_t xBytesSent;
char *pcStringToSend = "String to send";
BaseType_t xHigherPriorityTaskWoken = pdFALSE; // Initialised to pdFALSE.
// Attempt to send the string to the message buffer.
xBytesSent = xMessageBufferSendFromISR( xMessageBuffer,
( void * ) pcStringToSend,
strlen( pcStringToSend ),
&xHigherPriorityTaskWoken );
if( xBytesSent != strlen( pcStringToSend ) )
{
// The string could not be added to the message buffer because there was
// not enough free space in the buffer.
}
// If xHigherPriorityTaskWoken was set to pdTRUE inside
// xMessageBufferSendFromISR() then a task that has a priority above the
// priority of the currently executing task was unblocked and a context
// switch should be performed to ensure the ISR returns to the unblocked
// task. In most FreeRTOS ports this is done by simply passing
// xHigherPriorityTaskWoken into portYIELD_FROM_ISR(), which will test the
// variables value, and perform the context switch if necessary. Check the
// documentation for the port in use for port specific instructions.
portYIELD_FROM_ISR( xHigherPriorityTaskWoken );
}
Receives a discrete message from a message buffer. Messages can be of variable length and are copied out of the buffer. ***NOTE***: Uniquely among FreeRTOS objects, the stream buffer implementation (so also the message buffer implementation, as message buffers are built on top of stream buffers) assumes there is only one task or interrupt that will write to the buffer (the writer), and only one task or interrupt that will read from the buffer (the reader). It is safe for the writer and reader to be different tasks or interrupts, but, unlike other FreeRTOS objects, it is not safe to have multiple different writers or multiple different readers. If there are to be multiple different writers then the application writer must place each call to a writing API function (such as xMessageBufferSend()) inside a critical section and set the send block time to 0. Likewise, if there are to be multiple different readers then the application writer must place each call to a reading API function (such as xMessageBufferRead()) inside a critical section and set the receive block time to 0. Use xMessageBufferReceive() to read from a message buffer from a task. Use xMessageBufferReceiveFromISR() to read from a message buffer from an interrupt service routine (ISR). Example use:
{c}
void vAFunction( MessageBuffer_t xMessageBuffer )
{
uint8_t ucRxData[ 20 ];
size_t xReceivedBytes;
const TickType_t xBlockTime = pdMS_TO_TICKS( 20 );
// Receive the next message from the message buffer. Wait in the Blocked
// state (so not using any CPU processing time) for a maximum of 100ms for
// a message to become available.
xReceivedBytes = xMessageBufferReceive( xMessageBuffer,
( void * ) ucRxData,
sizeof( ucRxData ),
xBlockTime );
if( xReceivedBytes > 0 )
{
// A ucRxData contains a message that is xReceivedBytes long. Process
// the message here....
}
}
An interrupt safe version of the API function that receives a discrete message from a message buffer. Messages can be of variable length and are copied out of the buffer. ***NOTE***: Uniquely among FreeRTOS objects, the stream buffer implementation (so also the message buffer implementation, as message buffers are built on top of stream buffers) assumes there is only one task or interrupt that will write to the buffer (the writer), and only one task or interrupt that will read from the buffer (the reader). It is safe for the writer and reader to be different tasks or interrupts, but, unlike other FreeRTOS objects, it is not safe to have multiple different writers or multiple different readers. If there are to be multiple different writers then the application writer must place each call to a writing API function (such as xMessageBufferSend()) inside a critical section and set the send block time to 0. Likewise, if there are to be multiple different readers then the application writer must place each call to a reading API function (such as xMessageBufferRead()) inside a critical section and set the receive block time to 0. Use xMessageBufferReceive() to read from a message buffer from a task. Use xMessageBufferReceiveFromISR() to read from a message buffer from an interrupt service routine (ISR). Example use:
{c}
// A message buffer that has already been created.
MessageBuffer_t xMessageBuffer;
void vAnInterruptServiceRoutine( void )
{
uint8_t ucRxData[ 20 ];
size_t xReceivedBytes;
BaseType_t xHigherPriorityTaskWoken = pdFALSE; // Initialised to pdFALSE.
// Receive the next message from the message buffer.
xReceivedBytes = xMessageBufferReceiveFromISR( xMessageBuffer,
( void * ) ucRxData,
sizeof( ucRxData ),
&xHigherPriorityTaskWoken );
if( xReceivedBytes > 0 )
{
// A ucRxData contains a message that is xReceivedBytes long. Process
// the message here....
}
// If xHigherPriorityTaskWoken was set to pdTRUE inside
// xMessageBufferReceiveFromISR() then a task that has a priority above the
// priority of the currently executing task was unblocked and a context
// switch should be performed to ensure the ISR returns to the unblocked
// task. In most FreeRTOS ports this is done by simply passing
// xHigherPriorityTaskWoken into portYIELD_FROM_ISR(), which will test the
// variables value, and perform the context switch if necessary. Check the
// documentation for the port in use for port specific instructions.
portYIELD_FROM_ISR( xHigherPriorityTaskWoken );
}
Tests to see if a message buffer is full. A message buffer is full if it cannot accept any more messages, of any size, until space is made available by a message being removed from the message buffer.
Tests to see if a message buffer is empty (does not contain any messages).
Resets a message buffer to its initial empty state, discarding any message it contained. A message buffer can only be reset if there are no tasks blocked on it.
message_buffer.h
{c}
size_t xMessageBufferSpaceAvailable( MessageBufferHandle_t xMessageBuffer );
Returns the number of bytes of free space in the message buffer. Returns the length (in bytes) of the next message in a message buffer. Useful if xMessageBufferReceive() returned 0 because the size of the buffer passed into xMessageBufferReceive() was too small to hold the next message.
For advanced users only. The sbSEND_COMPLETED() macro is called from within the FreeRTOS APIs when data is sent to a message buffer or stream buffer. If there was a task that was blocked on the message or stream buffer waiting for data to arrive then the sbSEND_COMPLETED() macro sends a notification to the task to remove it from the Blocked state. xMessageBufferSendCompletedFromISR() does the same thing. It is provided to enable application writers to implement their own version of sbSEND_COMPLETED(), and MUST NOT BE USED AT ANY OTHER TIME. See the example implemented in FreeRTOS/Demo/Minimal/MessageBufferAMP.c for additional information.
For advanced users only. The sbRECEIVE_COMPLETED() macro is called from within the FreeRTOS APIs when data is read out of a message buffer or stream buffer. If there was a task that was blocked on the message or stream buffer waiting for data to arrive then the sbRECEIVE_COMPLETED() macro sends a notification to the task to remove it from the Blocked state. xMessageBufferReceiveCompletedFromISR() does the same thing. It is provided to enable application writers to implement their own version of sbRECEIVE_COMPLETED(), and MUST NOT BE USED AT ANY OTHER TIME. See the example implemented in FreeRTOS/Demo/Minimal/MessageBufferAMP.c for additional information.
A version of xTimerStop() that can be called from an interrupt service routine. Example usage: @verbatim // This scenario assumes xTimer has already been created and started. When // an interrupt occurs, the timer should be simply stopped. // The interrupt service routine that stops the timer. void vAnExampleInterruptServiceRoutine( void ) { BaseType_t xHigherPriorityTaskWoken = pdFALSE; // The interrupt has occurred - simply stop the timer. // xHigherPriorityTaskWoken was set to pdFALSE where it was defined // (within this function). As this is an interrupt service routine, only // FreeRTOS API functions that end in "FromISR" can be used. if( xTimerStopFromISR( xTimer, &xHigherPriorityTaskWoken ) != pdPASS ) { // The stop command was not executed successfully. Take appropriate // action here. } // If xHigherPriorityTaskWoken equals pdTRUE, then a context switch // should be performed. The syntax required to perform a context switch // from inside an ISR varies from port to port, and from compiler to // compiler. Inspect the demos for the port you are using to find the // actual syntax required. if( xHigherPriorityTaskWoken != pdFALSE ) { // Call the interrupt safe yield function here (actual function // depends on the FreeRTOS port being used). } } @endverbatim
A version of xTimerChangePeriod() that can be called from an interrupt service routine. Example usage: @verbatim // This scenario assumes xTimer has already been created and started. When // an interrupt occurs, the period of xTimer should be changed to 500ms. // The interrupt service routine that changes the period of xTimer. void vAnExampleInterruptServiceRoutine( void ) { BaseType_t xHigherPriorityTaskWoken = pdFALSE; // The interrupt has occurred - change the period of xTimer to 500ms. // xHigherPriorityTaskWoken was set to pdFALSE where it was defined // (within this function). As this is an interrupt service routine, only // FreeRTOS API functions that end in "FromISR" can be used. if( xTimerChangePeriodFromISR( xTimer, &xHigherPriorityTaskWoken ) != pdPASS ) { // The command to change the timers period was not executed // successfully. Take appropriate action here. } // If xHigherPriorityTaskWoken equals pdTRUE, then a context switch // should be performed. The syntax required to perform a context switch // from inside an ISR varies from port to port, and from compiler to // compiler. Inspect the demos for the port you are using to find the // actual syntax required. if( xHigherPriorityTaskWoken != pdFALSE ) { // Call the interrupt safe yield function here (actual function // depends on the FreeRTOS port being used). } } @endverbatim
A version of xTimerReset() that can be called from an interrupt service routine. Example usage: @verbatim // This scenario assumes xBacklightTimer has already been created. When a // key is pressed, an LCD back-light is switched on. If 5 seconds pass // without a key being pressed, then the LCD back-light is switched off. In // this case, the timer is a one-shot timer, and unlike the example given for // the xTimerReset() function, the key press event handler is an interrupt // service routine. // The callback function assigned to the one-shot timer. In this case the // parameter is not used. void vBacklightTimerCallback( TimerHandle_t pxTimer ) { // The timer expired, therefore 5 seconds must have passed since a key // was pressed. Switch off the LCD back-light. vSetBacklightState( BACKLIGHT_OFF ); } // The key press interrupt service routine. void vKeyPressEventInterruptHandler( void ) { BaseType_t xHigherPriorityTaskWoken = pdFALSE; // Ensure the LCD back-light is on, then reset the timer that is // responsible for turning the back-light off after 5 seconds of // key inactivity. This is an interrupt service routine so can only // call FreeRTOS API functions that end in "FromISR". vSetBacklightState( BACKLIGHT_ON ); // xTimerStartFromISR() or xTimerResetFromISR() could be called here // as both cause the timer to re-calculate its expiry time. // xHigherPriorityTaskWoken was initialised to pdFALSE when it was // declared (in this function). if( xTimerResetFromISR( xBacklightTimer, &xHigherPriorityTaskWoken ) != pdPASS ) { // The reset command was not executed successfully. Take appropriate // action here. } // Perform the rest of the key processing here. // If xHigherPriorityTaskWoken equals pdTRUE, then a context switch // should be performed. The syntax required to perform a context switch // from inside an ISR varies from port to port, and from compiler to // compiler. Inspect the demos for the port you are using to find the // actual syntax required. if( xHigherPriorityTaskWoken != pdFALSE ) { // Call the interrupt safe yield function here (actual function // depends on the FreeRTOS port being used). } } @endverbatim
RTOS CALLOUT MACROS MAPPED TO RTOS PORT-SPECIFIC FUNCTIONS. Define callout macros used in generic Xtensa code to interact with the RTOS. The macros are simply the function names for use in calls from assembler code. Some of these functions may call back to generic functions in xtensa_context.h .
Dependencies
FreeRTOS depends on the following libraries: