[FreeRTOS] 11 software timer

The timer is MCU Common peripherals , We are bound to learn its hardware timer when learning all kinds of MCU . however ,MCU The self-contained hardware timer resources are limited , And it is generally used in places with strong real-time requirements .

stay freeRTOS The function of software timer is provided in , To achieve more timer resources . In this section, we will learn about software timers .

1）freeRTOS Software timer introduction

freeRTOS Software timer for , It can be set as a single execution 、 Periodically ;

When the fixed time expires , Will execute the callback function （ Interrupt service program equivalent to hardware timer ）;

Timer and callback function , You cannot call functions that block tasks , such as vTaskDelay()、vTaskDelayUntil() And waiting for semaphores 、 Functions like message queue , Otherwise, the timer will be abnormal .

Using software timer , Need to be in FreeRTOSConfig.h In file , take configUSE_TIMERS A macro is defined as 1.

freeRTOS Software timer for , It is realized through a task used inside the system , Namely prvTimerTask function , The mission is timers.c The document defines , It is generated by the system itself , Users can leave it alone .

Besides , stay FreeRTOSConfig.h In file , There are also some macro definitions that need attention , See the picture below ：

configTIMER_TASK_PRIORITY It defines the priority of timer tasks , Values can be 0~(configMAX_PRIORITIES-1), This value defines the timer task prvTimerTask The priority of the ;

configTIMER_QUEUE_LENGTH Defines the length of the timer queue , That is, it can define several software timers ;

configTIMER_TASK_STACK_DEPTH Defines the stack size of timer tasks , What is defined in the figure is 256 word , This stack is also the stack that the timer callback function will use , So we can't define it too small .

2） Common timer operation functions

freeRTOS The timer of is controlled by TimerHandle_t The type definition .

Create timer ：

TimerHandle_t xTimerCreate(

const char * const pcTimerName, /* Timer name , character string */

const TickType_t xTimerPeriod, /* Timer cycle , The unit is the system clock beat */

const UBaseType_t uxAutoReload, /* Single execution or periodic execution ,pdTRUE cycle ,pdFALSE A single */

void * const pvTimerID, /* Timer ID, This parameter is mainly used when multiple timers share a callback function , Get... In the callback function ID To identify which timer called it */

TimerCallbackFunction_t pxCallbackFunction /* Timer callback function */ );

This function actually creates timers dynamically , You can also use xTimerCreateStatic To statically create .

Another thing to be aware of , Timer callback function , It can only be defined in the following form ：(*TimerCallbackFunction_t)( TimerHandle_t xTimer ); That is, there is only one parameter passed in , Is the handle of the timer ;

Start timer ：

BaseType_t xTimerStart( TimerHandle_t xTimer,    /* Timer handle */

TickType_t xBlockTime ); /* The maximum waiting time before successfully starting the timer is set , The unit is the system clock beat */

This function can only be called in the task , If you want to start the timer in the interrupt , Need to use xTimerStartFromISR().

Stop timer ：

BaseType_t xTimerStop( TimerHandle_t xTimer,  /* Timer handle */

TickType_t xTicksToWait );/* The maximum waiting time before successfully stopping the timer , The unit is the system clock beat */

This function can only be called in the task , If you want to stop the timer in the interrupt , Need to use xTimerStopFromISR().

Get the of the timer ID value ：

void *pvTimerGetTimerID( TimerHandle_t xTimer ); /* The input parameter is timer handle , return ID */

3） Programming test

adopt cubemx After generating the project file , stay keil in , Three tasks are generated ：

Notice the task priority here ,defaultTask The priority of the osPriorityNormal Pass by HAL Transformation of library function , Corresponding freeRTOS Priority in 3

Let's first define the handles of three timers ：

Before starting the task , Create three timers , And activate them ：

Timer 01 and 02 Are set to work periodically , Timer 01 The period is 1s, Timer 02 The period is 2s; Timer 03 Just run 1 Time ; Here we are to test the timer ID Acquisition function , Let them share a callback function TimerCallback

The timer returns to the function TimerCallback The implementation is as follows , Get the of the timer ID, And print it out ：

stay defaultTask in , Time delay 10s Then stop three timers ：

compile , Download to the development board to run , The output of this program is as follows ：

You can see , Timer 01 Every time 1s To run a , Timer 02 Every time 2s To run a , Timer 03 Only in the first 3s It's running 1 Time . The test results are consistent with the timer settings .

The timer has been running 9s, This is because defaultTask The priority of is 3, and FreeRTOSConfig.h Priority of timer task in configTIMER_TASK_PRIORITY Define a 2, Than defaultTask Low priority , So in the first 10s when , First execute the timer stop , The timer callback function will no longer be called .

If you put configTIMER_TASK_PRIORITY The macro definition is changed to 4, Than defaultTask High priority , So the first 10s The timer task will be executed first ,defaultTask The operation of stopping the timer in will be executed after ; The output will be more than 10s The callback function prints twice , The test results are as follows ：

You can see that a total of 10s Information about .

Okay , That's all for this section .

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