PicoSDK
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Outline
#include "pico/sem.h"
#include "pico/time.h"
sem_init(semaphore_t *, int16_t, int16_t)
sem_available(semaphore_t *)
sem_acquire_blocking(semaphore_t *)
sem_acquire_timeout_ms(semaphore_t *, uint32_t)
sem_acquire_timeout_us(semaphore_t *, uint32_t)
sem_acquire_block_until(semaphore_t *, absolute_time_t)
sem_try_acquire(semaphore_t *)
sem_release(semaphore_t *)
sem_reset(semaphore_t *, int16_t)
Files
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SourceVuRaspberry Pi Pico SDK and ExamplesPicoSDKsrc/common/pico_sync/sem.c
 
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/* * Copyright (c) 2020 Raspberry Pi (Trading) Ltd. * * SPDX-License-Identifier: BSD-3-Clause *//* ... */ #include "pico/sem.h" #include "pico/time.h" void sem_init(semaphore_t *sem, int16_t initial_permits, int16_t max_permits) { lock_init(&sem->core, next_striped_spin_lock_num()); sem->permits = initial_permits; sem->max_permits = max_permits; __mem_fence_release(); }{ ... } int __time_critical_func(sem_available)(semaphore_t *sem) { #ifdef __GNUC__ return *(volatile typeof(sem->permits) *) &sem->permits; #else static_assert(sizeof(sem->permits) == 2, ""); return *(volatile int16_t *) &sem->permits;/* ... */ #endif ...} void __time_critical_func(sem_acquire_blocking)(semaphore_t *sem) { do { uint32_t save = spin_lock_blocking(sem->core.spin_lock); if (sem->permits > 0) { sem->permits--; spin_unlock(sem->core.spin_lock, save); break; }if (sem->permits > 0) { ... } lock_internal_spin_unlock_with_wait(&sem->core, save); ...} while (true); ...} bool __time_critical_func(sem_acquire_timeout_ms)(semaphore_t *sem, uint32_t timeout_ms) { return sem_acquire_block_until(sem, make_timeout_time_ms(timeout_ms)); ...} bool __time_critical_func(sem_acquire_timeout_us)(semaphore_t *sem, uint32_t timeout_us) { return sem_acquire_block_until(sem, make_timeout_time_us(timeout_us)); ...} bool __time_critical_func(sem_acquire_block_until)(semaphore_t *sem, absolute_time_t until) { do { uint32_t save = spin_lock_blocking(sem->core.spin_lock); if (sem->permits > 0) { sem->permits--; spin_unlock(sem->core.spin_lock, save); return true; }if (sem->permits > 0) { ... } if (lock_internal_spin_unlock_with_best_effort_wait_or_timeout(&sem->core, save, until)) { return false; }if (lock_internal_spin_unlock_with_best_effort_wait_or_timeout(&sem->core, save, until)) { ... } ...} while (true); ...} bool __time_critical_func(sem_try_acquire)(semaphore_t *sem) { uint32_t save = spin_lock_blocking(sem->core.spin_lock); if (sem->permits > 0) { sem->permits--; spin_unlock(sem->core.spin_lock, save); return true; }if (sem->permits > 0) { ... } spin_unlock(sem->core.spin_lock, save); return false; ...} // todo this should really have a blocking variant for when permits are maxed out bool __time_critical_func(sem_release)(semaphore_t *sem) { uint32_t save = spin_lock_blocking(sem->core.spin_lock); int32_t count = sem->permits; if (count < sem->max_permits) { sem->permits = (int16_t)(count + 1); lock_internal_spin_unlock_with_notify(&sem->core, save); return true; }if (count < sem->max_permits) { ... } else { spin_unlock(sem->core.spin_lock, save); return false; }else { ... } ...} void __time_critical_func(sem_reset)(semaphore_t *sem, int16_t permits) { assert(permits >= 0 && permits <= sem->max_permits); uint32_t save = spin_lock_blocking(sem->core.spin_lock); if (permits > sem->permits) { sem->permits = permits; lock_internal_spin_unlock_with_notify(&sem->core, save); }if (permits > sem->permits) { ... } else { sem->permits = permits; spin_unlock(sem->core.spin_lock, save); }else { ... } ...}
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