Possibility to dfu from Application - Using Dual Bank Bootloader

[nunomiguelferreira]

Is your feature request related to a problem? Please describe.
The addition of compiling a dual bank bootloader is ideal. Unfortunately when devices are deployed with a celular connection they still lack a proper method to update their firmware. It is trivial to download it to the bank1 address, but the bootloader as is does not seem to recognize the data as valid.

Describe the solution you'd like
Ideally we should be able to write to BANK1_Address and in a similar way we reset into OTADFU or SerialDFU, we should be able to tell the bootloader a new application has been downloaded to bank1 and to try and apply it with success, reverting if not possible.

Describe alternatives you've considered
There is some support for a similar feature in the sandeep mistry nrf core, using arduinoOTA. There is also some support in the official nrf connect forum like: https://devzone.nordicsemi.com/f/nordic-q-a/46994/background-dfu-application-source-code/187708

[ejtagle]

This should be doable, but the bootloader won't copy the BANK1 to the BANK0 (as it would be required). That is because on the bootloader code execution flow, there is no reset between the download to BANK1, the verification of the data and the copying to BANK0.
If your intent is JUST to update the application, not the bootloader or the softdevice, instead of adding this feature to the bootloader, it would be much easier to just copy the FLASH block copy function to SRAM, disable softdevice and all peripherals, execute the block copy routine resident in SRAM, and launch it,, so your own program does the copying from the BANK1 to the BANK0, and the just reset the chip. That should be enough
Yes, we could add a new value for NRF_POWER->GPREGRET, but... doing something along the following lines... would be easier:
(untested code follows)

Steps to Place Function in SRAM:
--> Compiler Attribute: Mark the function, for example:

__attribute__((section(".text_ram"))) void my_sram_function(void) {
// block copy from BANK1 to BANK0
...
NVIC_SysReset();
}

-- Linker Script Modification (.ld file): You must map this new .text_ram section into the RAM memory region.

ld
.text_ram :
{
    . = ALIGN(4);
    *(.text_ram)
    *(.text_ram.*)
    . = ALIGN(4);
} > RAM AT > FLASH

Note: > RAM AT > FLASH ensures the code is stored in FLASH but runs from RAM, requiring a copy mechanism during startup.

[nunomiguelferreira]

@ejtagle Thank you for your suggestion, I'll be sure to report back, hopefully with a success story! It is exactly what I need for my use case (the SoftDevice + Bootloader will be static, just need to be able to update the application itself, from the application)

[ejtagle]

https://devzone.nordicsemi.com/f/nordic-q-a/5966/how-to-execute-code-from-ram-on-nrf51-using-gcc-environment/20801#20801

Gives you an idea. All the functions called from this SRAM located function must reside in SRAM. So, probably, you will have to disable softdevice, all interrupts, and implement a FLASH block copy by hand, directly accessing the FLASH controller. Totally doable

You can take some code from here: https://github.com/andenore/NordicSnippets/blob/master/examples/nvmc/main.c

[nunomiguelferreira]

@ejtagle it worked out perfectly, after a reboot the new application is loaded ;) thanks for the help.

Even then I think this would would be a neat development for this bootloader if someone wants to take this challenge.