Path: utzoo!attcan!uunet!cs.utexas.edu!wuarchive!udel!mmdf
From: mike.irons@lynx.northeastern.edu
Newsgroups: comp.os.minix
Subject: (none)
Message-ID: <34809@nigel.ee.udel.edu>
Date: 29 Oct 90 03:19:35 GMT
Sender: mmdf@ee.udel.edu
Lines: 33


   How can one access the other DMA channels? I am working on a SCSI driver
and the board can do DMA, but it's in an AT. If I do polled IO, I can't have
parity checking on the transfer, so I wan't to implement the DMA.


	The Minix code for doing DMA only exists for xt_wini and floppy but no
AT DMA. Also the existing DMA code seems to assume a certain amount of previous
setup by the bios. The destination  memory location is loaded into the 
controller (and associated latch), but there doesn't seem to be any code to
tell the DMA controller where the floppy (and wini if you have an xt) is!

	I used to have the specs for the DMA controller, but don't anymore
(I moved into a dorm and couldn't afford the luxory of having so many data
manuals anymore) and I know that there is a way of setting the other end. 
You should be able to specify whether it's a IO/Memory location and the 
address on BOTH ends of the transfer, but Minix seems to only specify
the data buffer end of the transfer. 

	I can't just 'steal' a DMA channel (though the AT {channel 3}) seems
to be the best bet. If I use one of the channels that are described in the
code, I would have to 're-route' the hardware end on the DMA channel,
and if I use channel 3, well there's no port location info in the code
for that channel, so where do I load the buffer address?

	Could someone please send the info I need? It might be good to
document the chips completly in the code so people can work more easily
with adding features. Maybe use #defines like DMA_Cn_... where n = the
channel number, and putting in all the defines. Inthis case a little
overkill could help a student with there class project (which is the
whole point of Minix anyway).

		mike.irons%lynx@helios.northeastern.edu