(author's explaination):
Bit 15 is the flag to request a transmit complete interrupt. The
driver was apparently written to minimize interrupts, and if not for a
3-COM design quirk, everything would be just ducky.
Prior to loading the outbound packet into the FIFO, the driver checks
to see if there's enough space to contain the packet. If not, the
driver requests a transmit-available interrupt when there is
sufficient room. Unfortunately, the card is continuing to process the
prior FIFO, and by the time the driver sets the threshold for a
transmit available interrupt, the space is already available. When
this occurs, the 3COM card ignores the interrupt request, and the
driver is hung waiting for an interrupt that will never occur.
There's probably a more elegant solution, but requesting the transmit
complete interrupt was the easiest to implement. An alternative fix
might be to check free FIFO space again, after requesting the transmit
available interrupt, but I haven't bothered pursuing this. Since the
patch, my 3C590 (PCI, same FIFO interface as 3C509) has been rock
solid.
Submitted by: mevans@candle.com (Mike Evans)
39679ba053