xTimerCreate() function

TimerHandle_t xTimerCreate( const char * const pcTimerName, TickType_t xTimerPeriodInTicks, UBaseType_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 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 http://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 ), // 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