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.