Firmware Reset failing with MCUboot and WDT

[hugzy123]

Hi all,

We have an application which uses both MCUboot and a watchdog timer. This combination seems to be causing issues anytime we attempt a soft reset using sys_reboot or NVIC reset directly.

Our system;

• Custom board using nRF5340
• ncs v2.2.0

When we attempt a soft reset the following happens;

1. Device powers down and enters bg_thread_main() in "ncs\v2.2.0\zephyr\kernel\init.c", it doesn't enter our application main()
2. Device enters MCUboot
3. After sometime the watchdog resets, the device enters MCUboot again
4. Finally the device enters bg_thread_main() again, this time our application main() runs successfully

All this is monitored using UART log (shown below).

This issue looks similar to another devzone post, however, we've tried the suggestion of adding CONFIG_BOOT_WATCHDOG_FEED to our mcuboot.conf but we still get the same sequence of events.

From the RESET table, software resets don't reset the WDT which explains why we get 2 resets but it doesn't explain why we don't enter our application main loop in 1. We've tried forcing a WDT timer reset instead of a soft reset and this does fix the issue - we only get one reset and it enters our application main loop successfully. 

One solution is if we tie a gpio directly to the RESET pin and use this gpio for resets from within the application. This isn't ideal as it requires hardware changes and limits ours design.

Does anyone have any other suggestions we can try?

[Vidar Berg]

Hello,

The CONFIG_BOOT_WATCHDOG_FEED symbol should be selected by default when the build target is a nRF device. You can confirm this by if the symbol is set in the generated configuration file (build/mcuboot/zephyr/.conf). Either way, I would suggest that you try to make the WD timeout longer (e.g., 30 seconds), if you have not done so already. Then debug the device to see where it hangs when the program isn't reaching main().

Thanks,

Vidar

[hugzy123]

Hi Vidar,

Thanks for your reply.

You're right that the "CONFIG_BOOT_WATCHDOG_FEED" option is included by default in the mcuboot configuration.

From what I can tell, it seems the application is hanging on the main() function inside bg_thread_main(). All the functions called before main() appear to be exiting without any issues.

[Vidar Berg]

Hi,

hugzy123 said:

From what I can tell, it seems the application is hanging on the main() function inside bg_thread_main(). All the functions called before main() appear to be exiting without any issues.

I would have expected the "boot banner" to be printed before the WD reset if the system initialization in bg_thread_main() completed succesfully. 

https://github.com/nrfconnect/sdk-zephyr/blob/c0689b16ff127d1b71a4cc20310d476e1807e26e/kernel/init.c#L297 

Could you place a breakpoint at the call to z_sys_init_run_level(INIT_LEVEL_POST_KERNEL); and another at the call to z_sys_init_run_level(INIT_LEVEL_APPLICATION); to check if both are reached?

[hugzy123]

Vidar Berg said:

I would have expected the "boot banner" to be printed before the WD reset if the system initialization in bg_thread_main() completed succesfully. 

There is a boot banner being printed, its actually printed three times; once just after the application reset, a second after the first bootloader sequence has finished and a third after the WDT reset and the second bootloader sequence.

Vidar Berg said:

Could you place a breakpoint at the call to z_sys_init_run_level(INIT_LEVEL_POST_KERNEL); and another at the call to z_sys_init_run_level(INIT_LEVEL_APPLICATION); to check if both are reached?

I'm using UART so I can't use breakpoints, however, I have added multiple log messages and observed the application reaches just before main(); in the function bg_thread_main on the first failed reset attempt (before the WDT reset). 

 

[Vidar Berg]

The boot banner is printed during system initialization in bg_thread_main(), so normally it should appear once during the startup of mcuboot and then a second time when the application boots up.

Is it possible to attach a debugger to your custom board? If not, do you think it would be possible to reproduce this on a DK so I can try to debug it here?