Timer can not restart immediately when I call app_timer_stop() and app_timer_start() in timeout_handler.

[bob]

Dear Nordic team,

I am maintain firmware on nRF51802QFAA with SDK12.3.

It starts a timer within 5 seconds interval, in timeout_handler, it will read sensor data via i2C, then save data in flash memory via SPI.

When it is connected by mobile phone, phone will request data which is stored in flash memory, device will restart timer with 100 milliseconds interval. In timeout_handler function, it will read flash data one by one and send to mobile phone quickly.

Unfortunately, almost every time, the timeout_handler can not be triggered immediately after I call app_timer_stop() and app_timer_start(). I wait for about 30 seconds or even longer time, then timeout_handler is triggered. After this, it can be triggered every 100ms correctly.

Note:

(1) I set SPI priority to 2, while timer and I2C priority is 3.  Because I found SPI transfer will be blocked if its priority is set to 3. I think it is competing for cpu resources with timer & I2C.

(2) I already tried to put app_timer_stop() and app_timer_start() in CRITICAL_REGION_ENTER() and CRITICAL_REGION_EXIT() to help timer restarting well. But it help just a little, can not make timer restart immediately every time.

Can you please figure out how to fix this problem?

Many thanks!

Bob

[Jared]

Hi,

As you suspect there might be some priority conflict that is blocking the timer from start.

Do you observe the same issue if you decrease the priority of the SPI? 

regards

Jared

[bob]

I did set SPI priority to 3,  but SPI is blocked while timer is running.

[Jared]

Hi,

I think you need to go over your program and investigate what exactly that is blocking the app timer from running. One tip is that you want to avoid spending time in interrupt context as it can block other tasks from running in main context. 

regards

Jared 

[bob]

I debug the firmware,  when I call stop timer and start time, it hangs. I see disassembly code it stops on WFE and SEV. See below picture:

[bob]

I called nrf_delay_us(18000) in timeout_handler, will it block timer restart ?

[Jared]

I suggest that you try to comment out that line and see if you observe any difference

nrf_delays_us will make the CPU spin in a busy-wait loop. If called from main context then it will not block other interrupts with higher priorities, if called from interrupt context such as callback handlers, then it will most likely block other tasks.

regards

Jared