# configUSE\_TICKLESS\_IDLE **URL:** \ **Category:** Kernel\ **Created:** [April 4, 2014, 2:20am UTC](https://forums.freertos.org/t/configuse-tickless-idle/4177 "2014-04-04T02:20:55Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![system](https://d2v6vdsk2p900z.cloudfront.net/original/1X/7fc8fdb729c645aab5b20282bbe34e57cb407be6.jpeg) [@system](https://forums.freertos.org/u/system)\ **Post date:** [April 4, 2014, 2:20am UTC](https://forums.freertos.org/t/configuse-tickless-idle/4177/1 "2014-04-04T02:20:55Z")
**[l4n4](https://sourceforge.net/u/l4n4/)** wrote on [Friday, April 04, 2014](https://sourceforge.net/p/freertos/discussion/382005/thread/b86a64f0/#e25f): If we enable the configUSE\_TICKLESS\_IDLE, it will go to ‘idle’ only when the xExpectedIdleTime \>= 2. Do you think , it’s worthwhile to call the \_\_WFI (wait for interrupt) even if the xExpectedIdleTime is \< 2 (in term of power saving)? I’m running a 180Mhz cortex M3. if( xExpectedIdleTime \>= configEXPECTED\_IDLE\_TIME\_BEFORE\_SLEEP ) { portSUPPRESS\_TICKS\_AND\_SLEEP( xExpectedIdleTime ); } else{ \_\_WFI(); //add wait for interrupt here } ---
**Author:** ![rtel](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/rtel/32/31_2.png) [@rtel](https://forums.freertos.org/u/rtel)\ **Post date:** [April 4, 2014, 3:14am UTC](https://forums.freertos.org/t/configuse-tickless-idle/4177/2 "2014-04-04T03:14:51Z")
**[rtel](https://sourceforge.net/u/rtel/)** wrote on [Friday, April 04, 2014](https://sourceforge.net/p/freertos/discussion/382005/thread/b86a64f0/#2d28): It may be that, in your particular application, you get some benefit from doing that, but if so I would not recommend changing the source code in that way but instead define an idle hook function that just calls wfi. Regards. ---
**Author:** ![system](https://d2v6vdsk2p900z.cloudfront.net/original/1X/7fc8fdb729c645aab5b20282bbe34e57cb407be6.jpeg) [@system](https://forums.freertos.org/u/system)\ **Post date:** [April 4, 2014, 3:38am UTC](https://forums.freertos.org/t/configuse-tickless-idle/4177/3 "2014-04-04T03:38:55Z")
**[l4n4](https://sourceforge.net/u/l4n4/)** wrote on [Friday, April 04, 2014](https://sourceforge.net/p/freertos/discussion/382005/thread/b86a64f0/#3cf4): The idle hook will be called all the time and before portSUPPRESS\_TICKS\_AND\_SLEEP, so it will always sleep for 1 tick time first before do any further checks. This means : - if xExpectedIdleTime \< 2 : this is ok - if xExpectedIdleTime == 2 : Idle hook will sleep for 1 tick and portSUPPRESS\_TICKS\_AND\_SLEEP will not be called. I would like the portSUPPRESS\_TICKS\_AND\_SLEEP to be called in this condition. - xExpectedIdleTime \> 2 : this is ok Thanks! ---
**Author:** ![rtel](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/rtel/32/31_2.png) [@rtel](https://forums.freertos.org/u/rtel)\ **Post date:** [April 4, 2014, 3:01pm UTC](https://forums.freertos.org/t/configuse-tickless-idle/4177/4 "2014-04-04T15:01:39Z")
**[rtel](https://sourceforge.net/u/rtel/)** wrote on [Friday, April 04, 2014](https://sourceforge.net/p/freertos/discussion/382005/thread/b86a64f0/#89c2): How about setting configEXPECTED\_IDLE\_TIME\_BEFORE\_SLEEP to 0 (may cause a compiler warning where the \>= check is performed) then use the [configPRE\_SLEEP\_PROCESSING](http://www.freertos.org/low-power-ARM-cortex-rtos.html) to check the expected idle time and if the expected idle time is below a threshold set by yourself it can just call wfi and cancel the tickless entry (the macros parameter can be used for cancelling the tickless entry). Regards. ---
**Author:** ![system](https://d2v6vdsk2p900z.cloudfront.net/original/1X/7fc8fdb729c645aab5b20282bbe34e57cb407be6.jpeg) [@system](https://forums.freertos.org/u/system)\ **Post date:** [January 10, 2017, 4:31pm UTC](https://forums.freertos.org/t/configuse-tickless-idle/4177/5 "2017-01-10T16:31:12Z")
**[mplmht](https://sourceforge.net/u/mplmht/)** wrote on [Tuesday, January 10, 2017](https://sourceforge.net/p/freertos/discussion/382005/thread/b86a64f0/#c965): I have the same concern here but I would like to keep usage of configEXPECTED\_IDLE\_TIME\_BEFORE\_SLEEP functionnality which is interesting I beleive. I would like to get your advice on following code change proposal: - when tickless idle feature is enabled, call to the idle hook when xExpectedIdleTime is below configEXPECTED\_IDLE\_TIME\_BEFORE\_SLEEP - when tickless idle feature is not enabled, keep calling the idle hook the same way as now. The code change could look like below in portTASK\_FUNCTION function of tasks.c (line 3177 of v9.0.0)? ``` #if ( configUSE_TICKLESS_IDLE == 0 ) #if ( configUSE_IDLE_HOOK == 1 ) { extern void vApplicationIdleHook( void ); /* Call the user defined function from within the idle task. This allows the application designer to add background functionality without the overhead of a separate task. NOTE: vApplicationIdleHook() MUST NOT, UNDER ANY CIRCUMSTANCES, CALL A FUNCTION THAT MIGHT BLOCK. */ vApplicationIdleHook(); } #endif /* ( configUSE_IDLE_HOOK == 1 ) */ /* This conditional compilation should use inequality to 0, not equality to 1. This is to ensure portSUPPRESS_TICKS_AND_SLEEP() is called when user defined low power mode implementations require configUSE_TICKLESS_IDLE to be set to a value other than 1. */ #else /* configUSE_TICKLESS_IDLE != 0 */ { TickType_t xExpectedIdleTime; /* It is not desirable to suspend then resume the scheduler on each iteration of the idle task. Therefore, a preliminary test of the expected idle time is performed without the scheduler suspended. The result here is not necessarily valid. */ xExpectedIdleTime = prvGetExpectedIdleTime(); if( xExpectedIdleTime >= configEXPECTED_IDLE_TIME_BEFORE_SLEEP ) { vTaskSuspendAll(); { /* Now the scheduler is suspended, the expected idle time can be sampled again, and this time its value can be used. */ configASSERT( xNextTaskUnblockTime >= xTickCount ); xExpectedIdleTime = prvGetExpectedIdleTime(); if( xExpectedIdleTime >= configEXPECTED_IDLE_TIME_BEFORE_SLEEP ) { traceLOW_POWER_IDLE_BEGIN(); portSUPPRESS_TICKS_AND_SLEEP( xExpectedIdleTime ); traceLOW_POWER_IDLE_END(); } else { mtCOVERAGE_TEST_MARKER(); #if ( configUSE_IDLE_HOOK == 1 ) { extern void vApplicationIdleHook( void ); /* Call the user defined function from within the idle task. This allows the application designer to add background functionality without the overhead of a separate task. NOTE: vApplicationIdleHook() MUST NOT, UNDER ANY CIRCUMSTANCES, CALL A FUNCTION THAT MIGHT BLOCK. */ vApplicationIdleHook(); } #endif /* configUSE_IDLE_HOOK */ } } ( void ) xTaskResumeAll(); } else { mtCOVERAGE_TEST_MARKER(); } } #endif /* configUSE_TICKLESS_IDLE */ ``` Regards. ---
**Author:** ![rtel](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/rtel/32/31_2.png) [@rtel](https://forums.freertos.org/u/rtel)\ **Post date:** [January 10, 2017, 5:12pm UTC](https://forums.freertos.org/t/configuse-tickless-idle/4177/6 "2017-01-10T17:12:03Z")
**[rtel](https://sourceforge.net/u/rtel/)** wrote on [Tuesday, January 10, 2017](https://sourceforge.net/p/freertos/discussion/382005/thread/b86a64f0/#c965/1ca9): Hi - thanks for your input, although I doubt this would be adopted because it would change the existing behaviour, which could cause issues for users that update the version of FreeRTOS they are using in existing applications.