Silicon Labs uses what they call the “MINI-S” debug interface instead of the standard ARM SWD pinout for their 2x5 1.27mm debug connectors.

On one hand this is nice because it uses the extra pins for UART and radio trace, but on the other hand it means I can’t just plug my debugger in to the target board.

So, I built a little adapter PCB to break out a standard SWD connector and a header for the UART TX/RX, with the option of routing SWO or UART-TX to the SWO pin on the SWD debugger:

Want one? You can order 3 PCBs from OSHPARK for $2.50 or download the gerbers for manufacture elsewhere.