Chapter 2. API Reference
Timer API
Header File
• components/freertos/include/freertos/timers.h
Functions
TimerHandle_t xTimerCreate(const char *const pcTimerName, const TickType_t xTimerPeriod-
InTicks, const UBaseType_t uxAutoReload, void *const pvTimerID,
TimerCallbackFunction_t pxCallbackFunction)
TimerHandle_t xTimerCreate( const char * const pcTimerName, TickType_t xTimerPeriodInTicks, UBase-
Type_t uxAutoReload, void * pvTimerID, TimerCallbackFunction_t pxCallbackFunction );
Creates a new software timer instance, and returns a handle by which the created software timer can be refer-
enced.
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 auto-
matically 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(), xTimer-
ResetFromISR(), xTimerChangePeriod() and xTimerChangePeriodFromISR() API functions can all be used
to transition a timer into the active state.
Example usage:
* #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 );
* }
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Espressif Systems 914
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