Steven Hirsch wrote about the AT&T Unix PC (7300 or 3B1):
At a hardware level, there is sufficient information available to
produce some sort of "combo" card. However, to the best of my
knowledge the kernel sources never leaked out. Without that, I think
the chances of producing a robust TCP stack are about zeo.
However, the
".o" files for the kernel were available, which makes it
somewhat more practical to hack than a linked kernel.
At one time I was met someone who had the kernel sources, but was of
course unable to give them to me.
Eric