I'd like to be able to connect a serial terminal to this board so that I can run a RISC-V core and get serial data to/from it. How would I go about doing this?
There should already be debug uart pins, check GPIO12 and GPIO13 of the RPi. The DirtyJTAG software should enabled them already:
https://github.com/phdussud/pico-dirtyJtag
https://github.com/phdussud/pico-dirtyJtag?tab=readme-ov-file#debug-uart
We haven't tested it, additional work might be needed on the RISC to output to those pins.