I changed the baud rate of the serial printer to 2400 in the source code and could get bytes from the c64 but only on the user port channel 2.
Printers are supposed to be on channel 4 or 5 on the c64 iec bus, however there aren't any iec drivers that work, there's vic1515 but it's just a skeleton.
I was really keen on trying to get an okimate 20 print going, since its graphics commands are pretty simple and I had always wanted an oki.
I can get the user port to connect and send bytes.
But the c64 wants printers on 4...
I did find an okimate 20 apple2 disc on archive but it was in a2r format.