The only way back from this seems to be to reprogramme the bootloader itself, which requires the use of the SWD pads on the underside of the board. Basically the bootloader won’t kick in at all. If you are having problems, then it might be worth rebooting into bootloader mode, which you know is “listening” to the COM port, but the Arduino environment won’t “know the difference” as it were…īut one thing I have found is that it is also possible to “brick” the Xiao such that it no longer responds to reset, doesn’t illuminate the user LED and doesn’t even appear as a COM port any more at all. This is common to other Samd21 devices too, so this might be worth trying: Adafruit Trinket M0 Moving COM Ports in Arduino. Some of this might be related to the fact that the serial port presented in bootloader mode is a different serial port to that presented when running firmware. There is a brilliant description of the issue here in section 6: “Uploading/Bootloader/COM Port/Reset Problem”:
It is the same issue one gets with the ATmega32U4 based devices – essentially the main processor has to handle the USB stack as well as the application code and if something goes wrong, then USB communications is lost too. However this is very common on any microcontroller that does not have a separate “USB co-processor” to handle the USB communications. Yet triggering a reset at all is very fiddly, requiring the temporary connecting of two pads on the board itself.
it appears as a disk waiting for a UF2 file) and then resetting back again may work. Sometimes hitting reset twice to get the board into “bootloader” mode (i.e. It would appear that getting the timing of the reset of the board right compared to the upload action seems quite critical. I have found uploading sketches to the Xiao as it comes “out of the box” to be somewhat “hit and miss”. This is all detailed in the Seeed wiki here. To get up and running requires the Xiao Samd core which can be added to the Arduino board manager using the following URL and then installed in the usual way: I’ve had a few Seeed Xiao Samd boards (previously called Seeeduino Xiao) kicking around so decided to finally have a bit of a play with them and the Arduino environment.
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