preparation for tsunami support. Previous chipsets' direct-mapped DMA
mask was always 1024*1024*1024. The Tsunami chipset needs it to be
2*1024*1024*1024
These changes should not affect the i386 port
Reviewed by: Doug Rabson <dfr@nlsystems.com>
ADMtek AL981 "Comet" chipset. The AL981 is yet another DEC tulip clone,
except with simpler receive filter options. The AL981 has a built-in
transceiver, power management support, wake on LAN and flow control.
This chip performs extremely well; it's on par with the ASIX chipset
in terms of speed, which is pretty good (it can do 11.5MB/sec with TCP
easily).
I would have committed this driver sooner, except I ran into one problem
with the AL981 that required a workaround. When the chip is transmitting
at full speed, it will sometimes wedge if you queue a series of packets
that wrap from the end of the transmit descriptor list back to the
beginning. I can't explain why this happens, and none of the other tulip
clones behave this way. The workaround this is to just watch for the end
of the transmit ring and make sure that al_start() breaks out of its
packet queuing loop and waiting until the current batch of transmissions
completes before wrapping back to the start of the ring. Fortunately, this
does not significantly impact transmit performance.
This is one of those things that takes weeks of analysis just to come
up with two or three lines of code changes.
