nrf52832 custom simple bootloader implementation.

[Ivan]

Hi everybody.
I know that it is complete standart question, which has many asks and solutions here.
I'm quite new to bootloader management stuff.
So asking about some targeting recommendations and solutions, some custom examples to start with.

My goal is to implement kind of bootloader (no need of heavy original one with DFU, encryption and a lot of extra bloating stuff)
I only need such functionality:
 - Have some kind of extra program (actually bootloader), starts from different memory address from original app.
 - Ability to boot to this program on some event from main app. and only thing to do is copy new FW from some flash area to main program area.
Inside of a boot program can implement simple progress of copying like LED blink stuff or so
 - After that restart app and boot to main app.

Encryption of FW doesn't needed. Let has it also on a point that FW on flash has already verified and only ready for copying to main program area.

Does it possible to make it based on some simple example, not using Softdevice and a lot of extra original bootloader implementation?
Even more, does this procedure described above actually possible at all?

King regards.
Ivan.
 

[Dmitry]

Hi,

there's no need for bootloader in your case. Assuming you're not concerned about troubles while updating (otherwise there should be full-featured bootloader with DFU), just write a short piece of code that can be copied to RAM and started by main firmware after disabling softdevice and interrupts. This code will copy firmware (using NVMC registers) and reboot device.

[Ivan]

So, you mean that I can handle this from one app.?
Just on some trigger, start some other program in RAM with ability to FLASH to FLASH memory copying to main app start address, and after completing this procedure just reset and start main app again based on new FW now.

Maybe you can give some advices how to place some extra app. copying code to RAM and tell program to start execution from that address?

[Ivan]

And a more question. Can I do opposide procedure - read existing FW to some other part of flash, verify and than restart to main app again? As I understand it's a same procedure - some small readout code in RAM?

[Dmitry]

Yes, I made such scheme in my project. The copying procedure should be position-independent and should not use library functions (it's better to write it in assembly). One tricky thing is to properly jump to RAM address - you should increment address by 1 to ensure THUMB mode, and compiler may optimize this increment out. 

The jump can be done this way:

typedef void (*update_fw_proc)(void *dest, void *src, u32 size);

... copy procedure to ram_code_start ...

update_fw_proc updater = (update_fw_proc) (ram_code_start + 1);
__dsb(0xf);
__isb(0xf);
(updater)(flash_start_addr, new_firmware, new_firmware_size);

[Dmitry]

Yes you can, even without RAM routine, but I don't understand the purpose.. to make a backup?

[Ivan]

First, I was looking for FW placed on USB MSD based on FatFS, than my device can be recognized as mass storage, I can simply place .bin file, than read it inside and send over my ESB mesh network to next device and update FW there. But, nrf52832 has no USB, so the only way is to read it directly.
But how in this case I can understand my FW size and how much data actually read from flash?