freertos - configUSE_TICKLESS_IDLE-低功耗-idel状态下不产生sys tick
from : https://www.freertos.org/vTaskStepTick.html
1 系统idle 状态
the Idle task is the only task able to execute
idle 任务是 唯一任务时，系统进入idle 状态。
2 configUSE_TICKLESS_IDLE
设置为 1 时，系统进入idle 状态后，关闭系统定时器（即不再产生 sys tick 中断）
相关实现使用如下函数
2.1 portSUPPRESS_TICKS_AND_SLEEP( xIdleTime )
当系统进入idle 状态下，调用此函数。
移植者自己实现这个函数。
这个函数需要做的事情就是
1、关闭系统定时器 ；
2、【假设 systick timer 中断间隔是T 】 设置 另外一个低功耗定时器，在 T * xIdleTime 时间后发出中断
3、启用低功耗定时器；关闭系统定时器。
2.2 vTaskStepTick
void vTaskStepTick( TickType_t xTicksToJump );
在低功耗定时器的中断 唤醒系统后，调用这个函数。设置 系统停用 sys tick 中断后，过去的tick 数目。
3 示例：
1 /* First define the portSUPPRESS_TICKS_AND_SLEEP(). The parameter is the time, 2 in ticks, until the kernel next needs to execute. */ 3 #define portSUPPRESS_TICKS_AND_SLEEP( xIdleTime ) vApplicationSleep( xIdleTime ) 4 5 /* Define the function that is called by portSUPPRESS_TICKS_AND_SLEEP(). */ 6 void vApplicationSleep( TickType_t xExpectedIdleTime ) 7 { 8 unsigned long ulLowPowerTimeBeforeSleep, ulLowPowerTimeAfterSleep; 9 10 /* Read the current time from a time source that will remain operational 11 while the microcontroller is in a low power state. */ 12 ulLowPowerTimeBeforeSleep = ulGetExternalTime(); 13 14 /* Stop the timer that is generating the tick interrupt. */ 15 prvStopTickInterruptTimer(); 16 17 /* Configure an interrupt to bring the microcontroller out of its low power 18 state at the time the kernel next needs to execute. The interrupt must be 19 generated from a source that is remains operational when the microcontroller 20 is in a low power state. */ 21 vSetWakeTimeInterrupt( xExpectedIdleTime ); 22 23 /* Enter the low power state. */ 24 prvSleep(); 25 26 /* Determine how long the microcontroller was actually in a low power state 27 for, which will be less than xExpectedIdleTime if the microcontroller was 28 brought out of low power mode by an interrupt other than that configured by 29 the vSetWakeTimeInterrupt() call. Note that the scheduler is suspended 30 before portSUPPRESS_TICKS_AND_SLEEP() is called, and resumed when 31 portSUPPRESS_TICKS_AND_SLEEP() returns. Therefore no other tasks will 32 execute until this function completes. */ 33 ulLowPowerTimeAfterSleep = ulGetExternalTime(); 34 35 /* Correct the kernels tick count to account for the time the microcontroller 36 spent in its low power state. */ 37 vTaskStepTick( ulLowPowerTimeAfterSleep - ulLowPowerTimeBeforeSleep ); 38 39 /* Restart the timer that is generating the tick interrupt. */ 40 prvStartTickInterruptTimer(); 41 }
