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]

Thats fine, but how to actually set some function to this pointer?

Does this correct?

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

//some flash write and reset manage function
static void fw_copy_flash(void *dest, void *src, uint32_t size)
{   
     //some flash copy stuff here via NVMC
     //...
     NVIC_SystemReset();
}

//actualy a function trigger
void execute_fw_update() 
{
    update_fw_proc updater = fw_copy_flash;
    memcpy((void*)(ram_code_start + 1), (update_fw_proc)updater, sizeof(updater)); 
    __dsb(0xf);
    __isb(0xf);
    (updater)(flash_start, new_fw_data, new_firmware_size);
}

And how than after flash copy I can perform a reset, still in same function like
NVIC_SystemReset();

??

[Dmitry]

Some points:

1) start your update function with __disable_irq()

2) here you can find a code that writes to flash using NVMC, erasing is similar

3) it's better to explicitly inline an implementation of NVIC_SystemReset, different compilers may have different view about inlining

4) The right way of copying function body:

uint32_t src = (uint32_t) fw_copy_flash;
memcpy(ram_code_start, (void *)(src & ~1), ram_code_size);

You can find size of your function in map file generated by linker.

[Ivan]

Perfect, thanx!
Regarding to flash, can I use already exist functions from nrf_nvmc.h ?

like: 
void nrf_nvmc_page_erase(uint32_t address);
void nrf_nvmc_write_bytes(uint32_t address, const uint8_t * src, uint32_t num_bytes);

[Dmitry]

You can use code from these functions, but not call them (they're located in the flash that you're overwriting). And you need to unroll their code to your single function that you can copy from start to end.

[Ivan]

That I thought about. Right.
Gonna try to implement and test all this stuff together.
'll ask if wanna clarify smth else.
But, great thanks at all for such detailed help at all! : )