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 ...