<shameless plug>
There's another FPGA modem design that connects to an EPP port instead
of the serial port. Although targeted at 76.8kBit/s, it can do
from 9.6kBit/s to approx. 1MBit/s (although at 1MBit/s it
requires some host resources). The design will be presented
for example in this year's DCC proceedings. It can't yet
do 1.2k, but YAM can't do that terribly well either :-)
For a Linux driver see baycom_epp.c
</shameless plug>
Tom