can't update MCUboot, flash protected?

[frankbuss]

I'm trying to update MCUboot from the application. As a first test, I enabled the flash shell commands. I can erase somewhere within the flash without problems:

uart:~$ flash erase e0000 1000                                                                                                                                
Erase success.                                                                                                                                                

but when I try to erase the bootloader, I get a bus fault:

uart:~$ flash erase 0 1000                                                                                                                                    
[00:00:28.689,117] <err> os: ***** BUS FAULT *****                                                                                                            
[00:00:28.689,147] <err> os:   Precise data bus error                                                                                                         
[00:00:28.689,178] <err> os:   BFAR Address: 0x0                                                                                                              
[00:00:28.689,239] <err> os: r0/a1:  0x00000000  r1/a2:  0x00000000  r2/a3:  0xffffffff                                                                       
[00:00:28.689,239] <err> os: r3/a4:  0x50039000 r12/ip:  0x2000ffc8 r14/lr:  0x0001e5f5                                                                       
[00:00:28.689,270] <err> os:  xpsr:  0x21000000                                                                                                               
[00:00:28.689,300] <err> os: Faulting instruction address (r15/pc): 0x000206d4                                                                                
[00:00:28.689,331] <err> os: >>> ZEPHYR FATAL ERROR 0: CPU exception on CPU 0                                                                                 
[00:00:28.689,392] <err> os: Current thread: 0x2000eeb8 (shell_uart)

Do I need to unprotect the flash somehow? Problem is I need this without the JTAG interface, all from the application, because the board is already at the customer, and they can only update it OTA, and I need to change the signing key. So my idea is to add MCUboot to my application, and then on start to update the flash and overwrite the old MCUboot.

[frankbuss]

I think I found the problem: CONFIG_FPROTECT=y is set for MCUboot. This in turn sets the SPU flashregion registers for the MCUboot range, and also locks the registers. So I guess there is no way to unlock it from the application, without using an external programmer?

[Vidar Berg]

Hello,

I am afraid you will not be able to update the bootloader in your case. The flash protection is one thing (can only be disabled through a reset), but it is also unsafe to delete the bootloader while running the application. Any unexpected during the update would "brick" the device as the bootloader will be the first entry point after reset (assuming it starts at address 0x0).

MCUboot must be implemented as a second stage bootloader if you want to make it upgradable: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bootloader/README.html 

Best regards,

Vidar