I need a UPDI interface and my old AVR Dragon only did PDI, so time to make one.
YES I KNOW, you can use pymcuprog or similar SerialUPDI after shorting TX and RX with a ~1kOhm resistor, but I wanted to make this just for the fun. I also know jtag2updi used to be pretty bad, and slow, and SerialUPDI is fast, but I promise you it has gotten better, and this works flawlessly; I flashed my Atmega4809 chip with some Arduino code (thanks to MegaCoreX).
I also believe that SerialUPDI has some specific requirements re chipsets etc, and I just like sticking to my CP2104, so I rather something dedicated that I know will always work, and also does not require any python code etc – just native integration with the Arduino (Legacy) IDE!
Youtube link here. Also the great r/Arduino subreddit there and here! Else watch it inline: