So I was messing around adding a UPDI connector to the T817 board to test it with the JTAG Mk3 and the Atmel Ice.
I'm ASS_U_MEing that the UPDI link from the debug chip goes to high impedance when not actually debugging or programming so I wired up pin1 of the UPDI connector directly to PA0, so far no smoke.
Tried both the JTAG Mk3 (early version) and the Atmel Ice and they both work for programming, for a ~8K download it takes less than 6 sec for the JTAG Mk3 and just less that 5sec for the Atmel Ice. I think it took about 10sec using the on board debug/programmer.
ahem...pardon the use of the autographed golden ice in the photo.....