#1310 makes it easier to write from openocd with feather-m4 and others.
However, two problems remain.

1. touchSerialPortAt1200bps() is executed when programmer is specified

As for 1, the following json does not have the flash-1200-bps-reset setting and will not cause a problem.
However, it is not reasonable to separate json, so you need to set flash-1200-bps-reset = false when -programmer is specified.

{
    "inherits": ["atsamd51j19a"],
    "build-tags": ["sam", "atsamd51j19a", "feather_m4"]
}

If you solve this problem, we will be able to write to the board in panic state.
(Normally flash-1200-bps-reset cannot be performed on a board in panic state.)

Also, we will be able to do rewrites very quickly.

2. Sometimes bootloader mode is triggered after writing

I think the reason for this problem is that the reset is performed multiple times when writing.
I don't know why, but changing program *.hex reset exit to program *.hex verify reset exit solved the problem.
I don't know if this is the right solution, but I'd like to fix it in some way.