SAMD21 burning bootloader with gdb / black magic probe

Hi all,

I follow these steps to burn the bootloader to SAMD21 ... the process was successful but after I upload a sketch from Arduino IDE , sometimes the bootloader went away and I lost the serial port and have to re-burn the bootloader using the SWD pins again....

I follow the steps below :-

On another site, I need to unlock the bootprot using the available commands in gdb for samd21

(gdb) monitor unlock_flash
(gdb) monitor unlock_bootprot
(gdb) monitor erase_mass

I read that I have to burn some fuses before I can write to the bootloader ..

I'm now totally confused ...

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