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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

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    found the bug, but i think there needs to be some big changes to solve this. The problem was that when gpio_irqhandler is caller in gpio irq context, it is most of the time waking the chip. In tickless mode the RTC counter is ticking but since the interrupts were disabled FreeRTOS tick is way behind when the ISR is called. When we call xTimerResetFromIsr, then the system tick is still not updated and stays the same as the one that was before going to sleep. We need a mechanism to update the tick when an interrupt have woken the chip in tickless mode. I tested this concept with a prototype and i can confirm that this is the problem we are seeing. Would you like to test this aswell? i will attach a patch but PLEASE DO NOT USE THIS PATCH in final product. We need to address this in a better way. patch coming up in a minute.

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  • 0

    found the bug, but i think there needs to be some big changes to solve this. The problem was that when gpio_irqhandler is caller in gpio irq context, it is most of the time waking the chip. In tickless mode the RTC counter is ticking but since the interrupts were disabled FreeRTOS tick is way behind when the ISR is called. When we call xTimerResetFromIsr, then the system tick is still not updated and stays the same as the one that was before going to sleep. We need a mechanism to update the tick when an interrupt have woken the chip in tickless mode. I tested this concept with a prototype and i can confirm that this is the problem we are seeing. Would you like to test this aswell? i will attach a patch but PLEASE DO NOT USE THIS PATCH in final product. We need to address this in a better way. patch coming up in a minute.

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