I am creating my own custom board using the ATSAMD21J18A chip. I am interested in being able to program it over the USB port with minimal additional pins needed.
I am considering the "AT07175: SAM-BA Bootloader for SAM D21", which I understand I have to get preloaded on my chip or program myself over SWD (meaning I need to expose RESET, SWCLK, SWDIO, and GND through a header for one-time use).
Once that is done, I either need to expose pin PA15 to force the chip into bootloader or erase the application or reset vector. The Arduino Zero or Due does a soft erase over USB by "Opening and closing the Native port at the baud rate of 1200 bps triggers a “soft erase” procedure". Is this a feature of the Arduino or the chip? I.E. Is this an alternative to exposing pin PA15 to get into the bootloader? If so, what are the risks of bricking my chip if this operation fails during a reset attempt?