MB> and depends quite a lot on the exact behavior of the 
MB> peripheral.

y'know, i've been puzzling on this now, since Luns Tee's
comment. Why would a FIFO be memory-mapped?? i don't
see that m-m buys you anything on the ISA bus over port
i/o, and FIFOs don't have addresses. at least, not standard
FIFOs. that's why it's so easy to plug a 4Kx9 into the same
socket as a 2Kx9 when you get in trouble: same pinouts.

i just talked with some folks who are running DAQ boards
under Windows with DOS TSRs and were curious about using
Win VxDs instead. i looked at some old literature i had lying
about and hadn't read...Windows VIRTUALIZES all the PC
IRQ and DMA stuff! Literally! Talk about a VDM! They got a
virtual 8259 and virtual interrupt table and virtual DMA into
virtual mem...oops! It's WHERE on the swapfile? Uh-oh. So
you make this buffer in real memory...sheesh.

I was wondering why all the DAQ boards were growing 7201
and 7202 FIFOs and dual DMA channels. Virt. IRQ response is
sorta like DOS emulation on RISC: pathetically slow. That got
me thinking about OS/2's drivers.  Without getting a DDDK
for OS/2 is there a good ref. on how IRQs and DMA are handled?
I presume something more civilized is used to feed the VDMs.

I guess "Writing OS/2 Device Drivers in C" would be one book.

___
 X KWQ/2 1.2g X 3 deg. K: Not with a bang, but a whimper.

--- Maximus/2 2.02