gatt_svc_access() function

Access callback whenever a characteristic/descriptor is read or written to. Here reads and writes need to be handled. ctxt->op tells weather the operation is read or write and weather it is on a characteristic or descriptor, ctxt->dsc->uuid tells which characteristic/descriptor is accessed. attr_handle give the value handle of the attribute being accessed. Accordingly do: Append the value to ctxt->om if the operation is READ Write ctxt->om to the value if the operation is WRITE