Jump to bootloader (mcuboot) from application without button

[puz_md]

Hi, I'm currently getting familiar with mcuboot and DFU

First of all, thank you very much for the new Academy course that covers DFU!

If I understand correctly, to enter the bootloader (for Serial Recovery), the bootloader button has to be activated during startup.

Unfortunately, our hardware is very small and does not have a bootloader button. Is there any possibility to switch from the application into bootloader mode, just like when the button was pressed? E.g. send a specific command via USB (cdc_acm) to the application that enables mcuboot?

Further, is the overlay that I created for my main project (board_name.overlay) also applied to the mcuboot child? Or will I have to create a separate overlay file for mcuboot (child_image\mcuboot.overlay)?

Best regards,

Michael

[Vidar Berg]

Hello Michael,

I'm glad to hear that you enjoyed the DFU course!

If I understand correctly, to enter the bootloader (for Serial Recovery), the bootloader button has to be activated during startup.

Yes, you can use a button to signal the bootloader to enter Serial recovery on boot. Another option is to enable the CONFIG_BOOT_SERIAL_WAIT_FOR_DFU=y symbol in your bootloader build. This will make the bootloader always enter serial recovery on startup. 

Further, is the overlay that I created for my main project (board_name.overlay) also applied to the mcuboot child? Or will I have to create a separate overlay file for mcuboot (child_image\mcuboot.overlay)?

Yes, you will need to create a separate overlay for the mcuboot build. You can do this by creating a child_image folder, as you mentioned. https://developer.nordicsemi.com/nRF_Connect_SDK/doc/2.6.0/nrf/config_and_build/multi_image.html#permanent-configuration-changes-to-child-images 

Best regards,

Vidar

[puz_md]

Hello Vidar,

thanks for the fast reply. Waiting for DFU increases startup time, so we try to jump from the application into the bootloader under certain conditions. (This way, the bootloader entry could also be hidden or protected.) We used this concept in all our older products, as they are usually deployed in the field and it is not feasible to perform a power cycle for entering the bootloader.

If I understand correctly, there is no such feature for enabling recovery mode from the application yet? Are there any plans to implement it in the future?

As a dirty workaround, would it be possible to set a digital output pin in the application and then perform a reset (how can I perform a reset) and the bootloader reads the pin that I just set as a "pressed button"?

Best regards,

Michael

[Vidar Berg]

Hello Michael,

It is currently not implemented, but you can use the the GPREGRET register like in the nRF5 SDK or use Retention System and have the application store a flag to signal the bootloader to enter serial recovery mode on next reboot. 

You can trigger an NVIC_SystemReset() from the application by calling sys_reboot(0). 

This is where serial recovery mode is entered when CONFIG_BOOT_SERIAL_WAIT_FOR_DFU is enabled:

https://github.com/nrfconnect/sdk-mcuboot/blob/86af2de75205ec5f2c846a2393934360de22fde4/boot/zephyr/main.c#L505 

Best regards,

Vidar

[mlac]

Hi guys,

I want to achieve the same as Michael.

What are the pros and cons of using GPREGRET vs the retention system, Vidar? 

[Vidar Berg]

Hi,

If you aren't using the Retention System for anything else, then I would just use the GPREGRET register directly. I don't see any benefit of using the retnetion system in that case.

[mlac]

Thanks, Vidar.

How can I read/write GPREGRET in Zephyr?

[Vidar Berg]

You can include the NRF POWER HAL with '#include <hal/nrf_power.h>' and use the gpregret _set()/_get functions.

I also noticed that we now have introduced this new method to enter serial recovery mode: https://github.com/nrfconnect/sdk-mcuboot/blob/6869a65c9171849f1c50407b924e875fcc9d6e92/boot/zephyr/Kconfig.serial_recovery#L167. You may want to check if this symbol is available in the SDK version you are working with. In that case, it may be worth using the Retention System to avoid having to patch the mcuboot code.

[mlac]

Thanks for the reference! This has been trivial to implement based on https://docs.zephyrproject.org/latest/services/retention/index.html

I used the featured devicetree fragments and Kconfig options.