Why is the FreeRTOS function xTimerResetFromISR not working in tickless mode?

[jules]

Hi,

I modified the blinky_freertos example from SDK 12 slightly to perform the following:

I have one timer and one task. The task blinks a LED and then suspends. In the timer callback function (one second period) I resume the task to have a LED that blinks every second. I now want to synchronise my timer to the "1 pulse per second" output of GPS module. To achieve this, I create a interrupt routine that resets my timer and resumes my task (so if the timer is reset just before it would call its callback, my task is still resumed). I took care not to resume a task from the ISR with a priority higher than the task that was interrupted.

If I'm running this code with tickless mode off, everything behaves as I expect. I attached a scope screenshot that shows the blinking LED (blue) is nicely synchronized to the external interrupt (yellow). Now when I turn tickless mode on, the synchronization will fail. It looks like the end of the delay in the task is synchronized with with the interrupt, and not the start of the task. Is this a bug? If not, can anybody tell me what I'm doing wrong? Our application is battery powered so tickless mode is really a must have.

I attached my main.c, FreeRTOSConfig.h, makefile and two scope screencaps.

Thanks!

Jules

main.c updated

FreeRTOSConfig.h

tickless_off.png

tickless_on.png

blinky_freertos.rar

[Susheel Nuguru]

Hi Jules,

I fixed the bug that was causing the tick difference. but that apparently did not fix the issue of timerreset not functioning in tickless mode. Sorry for pre mature celebrations.

Anyhow you will like to add this fix to your code with this diff

diff --git a/external/freertos/portable/CMSIS/nrf52/port_cmsis_systick.c b/external/freertos/portable/CMSIS/nrf52/port_cmsis_systick.c
index d89381d..868052d 100644
--- a/external/freertos/portable/CMSIS/nrf52/port_cmsis_systick.c
+++ b/external/freertos/portable/CMSIS/nrf52/port_cmsis_systick.c
@@ -266,6 +266,12 @@ void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime )
         }
         configPOST_SLEEP_PROCESSING( xExpectedIdleTime );
         nrf_rtc_int_disable(portNRF_RTC_REG, NRF_RTC_INT_COMPARE0_MASK);
+
+        /* If we do not clear this pending bit then interrupt trigger caused by compare0 (compare0 is only used in tickless mode)
+         * pendbit will be confused as TICK in xPortSysTickHandler
+         */
+        NVIC_ClearPendingIRQ(portNRF_RTC_IRQn);
+
         NVIC_EnableIRQ(portNRF_RTC_IRQn);

         /* Correct the system ticks */

This will fix the tick difference issue you are seeing