OK so UPDI actually stands for Unified Program and Debug Interface (https://onlinedocs.microchip.com/pr/GUID-DDB0017E-84E3-4E77-AAE9-7AC4290E5E8B-en-US-4/index.html?GUID-9B349315-2842-4189-B88C-49F4E1055D7F) but this board is so smol and kute that i will call it the Unusually Playful Device Interfacer and pat it's head when it does a good job. it's designed to make programming modern ATtiny chips very easy because it has 3 or 5V power&logic select, power and transmit indicator LEDs, and a quick cable for poking into a breadboard. To test it we're using an RP2040 because we have CH340 via USB Host support (https://github.com/adafruit/Adafruit_TinyUSB_Arduino/commit/8d996db5075b278e903024d026342b9f6ec755af) - we transmit data from the hardware Serial port and make sure it's received by the USB serial port, and vice versa.