Serial bootloader watchdog and RTT print issue

[tommik]

Hello,

i am currently developing on nRF52840 using SDK 15.2.0. I have an application and a bootloader. I use the GPREGRET register to boot to bootloader.

I have an issue where the WDT does not get reloaded if i do not have a debug printout in the WDT reload request located in nrf_bootloader_wdt.c:

static void wdt_feed(void)
{
if (nrf_wdt_started())
{
for (nrf_wdt_rr_register_t i = NRF_WDT_RR0; i < NRF_WDT_RR7; i++)
{
if (nrf_wdt_reload_request_is_enabled(i))
{
nrf_wdt_reload_request_set(i);
NRF_LOG_INFO("Feed RR %d wdt", i);
}
}
}
}

Without the NRF_LOG_INFO printout, the wdt reset is performed after the reload period set in the application has expired. With the print, the reload seems to work and the WDT reset is not performed.

I tried using a delay instead of the printout but that did not help.

Is there some known issue that could be causing this?

BR,

tommi

[Hung Bui]

Hi Velho, 

This is pretty strange. 

Could you try to test using our buttonless dfu example and the stock DFU bootloader and enable WDT to test ? 
In our example we don't print RTT log inside wdt_feed(). 

Do you modify have any modification to the bootloader ? 

[tommik]

The bootloader is not modified save for the printout. I think i am experiencing the same issue as this: https://devzone.nordicsemi.com/f/nordic-q-a/35570/entering-dfu-via-gpreget-secure-bootloader-serial-example-not-feeding-wdt-in-sdkv15/

For some reason a trace print in the WDT feed also prevents the WDT reset.

I will test if making an own timer to feed the WDT fixes my issue, as it seems to have worked for others.

[tommik]

Ok, i think i got this. The WDT is fed in the "loop_forever"-function in the nrf_bootloader.c file. When there are no debug printouts, the wait_for_event() call puts the device to sleep, and there are no events -> the wdt is never fed. When there are debugs, the log is processed constantly, so wait_for_event() is never called and the processor does not sleep, meaning that the watchdog is fed periodically. The WDT feed timer does not work, as is the case with others. I had no success implementing my own timer function, i will try to make some event that wakes the processor periodically so that the WDT is fed.

[Hung Bui]

Hi Tommik, 

Thanks for updating.

It depends on how you configure the WDT, there is an option that the WDT shouldn't run when the CPU is in sleep mode. In that case you don't need to periodically wake the CPU up to feed the dog. In other case, a timer is needed. 

[tommik]

I tried setting NRFX_WDT_CONFIG_BEHAVIOUR to Pause in SLEEP and HALT in the main app. I use it when configuring the WDT as the value for the behaviour member of the nrf_drv_wdt_config_t struct. Changing it provided no difference in the operation.

The DFU timer did not work, because nrf_clock_lf_is_running() called in nrf_bootloader_dfu_timers.h returns true even though the clock is not running. Removing the check, and thus calling nrf_clock_task_trigger(NRF_CLOCK_TASK_LFCLKSTART) on timer init made the timers work for both the inactivity timer as well as for the wdt feed timer, and now the bootloader finally works, as the periodic interrupts wake the processor periodically.