Since Loonies 8192 has apparently not been ported to enough platforms yet, the PSX seems to be a nice porting target, especially since the SCPH-9002 I have here now has a PsNee modchip installed.
In addition to the working SCPH-9002, I picked up a broken SCPH-1002 at a flea market some months ago. It does not work, but it has a PSX serial port (obviously) that I want to re-use -- this way, I don't need to cut up the PSX serial cable, which could - in theory - still be used for playing PlayStation Link Cable games like Wipeout 2097 or Wipeout 3: Special Edition.
The "PS-side" of uploading serial code is available as PSXSERIAL on psxdev.net, it contain both an ISO and the Windows-based client program for uploading PSX EXE files. For Linux and macOS, az6667 has written the nifty pypsxserial which can do the same thing cross-platform in Python 3.
But first, to figure out which pins are used for serial transfer, the psx_siocable web page has a useful diagram:
Pin 2 is GND, pin 5 is TXD and pin 8 is RXD -- all using 3.3V logic.
For the SCPH-1002 console (others are likely similar) the pins that we need are the following on the underside of the board:
Soldering three jumper wires to these connections, and then adding a serial cable, and using a 3.3V "FT232RL FTDI USB to TTL Adapter" from Amazon plus a USB cable did the trick:
Next up was routing the three wires to the top of the board, and since I tossed the broken optical assembly already, it fit nicely where the CD was (and could be easily hidden by closing the lid):
What I finally settled on was hot-glueing the USB-to-serial adapter on top of the parallel port, since the case has enough free space there that it's easy to fit it there:
This dead PSX might be used in the future for other projects, like memory card reader, PSX controller adapter and others, but for now, it serves well as overkill PSX serial adapter.