Custom bootloader with softdevice with jump to a specific address of app

[marklander]

Hi!

I try to explain quickly my setup that is working, I am on nrf52805 and I have SD112 ( 7.2.0 ) onboard. I am ok with placing bootloader at specific address using linker file, working correctly and also jump to the app is working correctly. My bootloader is custom ( not using softdevice - application needs sd instead), i just receive data from uart, erase app flash and rewrite with it with new app. All working if fw is above SD.

My issue is that I have a firmware now with a custom header needed for signature verification, which introduces an offsett on starting address of my app ( 0x800 + BASEADDRR ), I am quite sure that I can instruct MBR+SD to jump there reading this post , but i can't get it working. My understanding is that:

When I reset from bootloader i have to:

• use SD_MBR_COMMAND_IRQ_FORWARD_ADDRESS_SET with my address plus the offset ( no more jump to 0x1000 default address )
• Reset and jump there

But seems not working, I can't understand if I need also to use in some way this mbr command NRF_MBR_COMMANDS_SD_MBR_COMMAND_VECTOR_TABLE_BASE_SET, but it's not clear to me ( and in this case it seems that I have to allocate a page for Settings right? ).

Thanks in advance!

[Vidar Berg]

Hi,

Yes, this is possible. However, rather than using SD_MBR_COMMAND_IRQ_FORWARD_ADDRESS_SET, you can use the SD_MBR_COMMAND_INIT_SD command. This will allow you to use the sd_softdevice_vector_table_base_set() function in your bootlaoder and change to a non-default interrupt forwarding address for the Softdevice. The application start sequence in the bootloader should be something like this:

1. Issue the SD_MBR_COMMAND_INIT_SD command through the sd_mbr_command() API. This will cause the reset handler of the Softdevice to be executed.

3. Disable interrupts globally

2. Now with the SD initialized, you can use sd_softdevice_vector_table_base_set() to set the Softdevice vector forwarding address to your application's vector table address.

3. Forward execution to main application. 

Best regards,

Vidar

[marklander]

Thanks! I will try the exact sequnce you are suggesting.

One thing i forgot...i am on rust. But i have all bindings to nrf mbr so i can emulate all the sequence.

Two questions:

What does the sofdevice SD_MBR_COMMAND_INIT_SD do exactly?

I have used sd_softdevice_vector_table_base_set function and seems that calling this a reset is issued immedeately ( while irq fuction does not reset ) am i right?

And do i need to reserve a flash page for settings for that command?

[marklander]

Ups! I got now that I am confusing sd_mbr_command_vector_table_base_set_t with sd_softdevice_vector_table_base_set!

So sd_softdevice_vector_table_base_set will take the starting address of application with offset...and then I have to jump there

[marklander]

Vidar Berg said:

Issue the SD_MBR_COMMAND_INIT_SD command through the sd_mbr_command() API. This will cause the reset handler of the Softdevice to be executed.

Hi Vidar Berg ,

probably i am missing something...

I tried your sequence and I still cannot see app starting...what i see is:

• SD_MBR_COMMAND_INIT_SD return 0 - so seems executed correctly ( maybe I did not specify that i don't us sd in bootloader, but I don't think I need to enable it )
• Disabled all interrupts.
• sd_softdevice_vector_table_base_set also returns 0 so seems correct...
• At the end i tried to jump to main app start address and also to 0x1000 but nothing seems happening...

Any advice on the sequence i made?

[Vidar Berg]

It looks like everything is working correctly up until the point where you try to make the "jump" to the application. Are you able to step through the app's start function with a debugger to see what happens?

Another thing you can try is to call 'nrfjprog --readregs' after the jump to the main app to read out the core registers. This may provide us with some clues as to what the problem is.