There are some interesting options there ...
My interest is in a real Ethernet device. I already did the work to
write a TCP/IP stack that runs well on old DOS machines (
http://www.brutman.com/mTCP ). Having an external device that does the
TCP/IP work for me is nice for machines that are more limited, but a
PCjr or PC clone doesn't need it.
I haven't looked at the Ethernet chipset solutions recently but the last
time I looked around I got hung up on the interfacing to an 8 bit PC
bus. A lot of them seemed to require a 16 bit bus.
In my ideal world I would have an Ethernet chipset that wires easily to
an 8 bit PC bus. (I can make that work on a PCjr.) If 16 bit is
required then it is not feasible for the jr without some circuit
hackery. In that ideal world the packet driver already exists and
works, assuming that you didn't wire the chip up in some strange way.
Lastly, the chipset can use I/O ports and an IRQ. But DMA is a no-no.
Which is fine because most Ethernet chipsets in that class don't use DMA
anyway.
Time to do some reading ...
Mike