Dirty Rotten DMA problem (?) Simultaneous tape & diskette use

[Ted Powell]

In article <1990Nov7.155748.12583 at oct1.UUCP> mason at oct1.UUCP (David Mason) writes:
>In article <1990Oct31.190027.8613 at informix.com> aland at infmx.informix.com
>(Colonel Panic) writes:
>>[...bad things happening when using both tape and floppy...]
>>kernel is going haywire.  Current pertinent kernel parms are DMAEXCL=0
>>(allow simultaneous DMA) and DMAABLEBUF=256.
>
>As a matter of interest, the Interactive 2.2 (== 3.2.2) release notes
>state the following, under "Known Problems and Bugs":
>        "On machines with certain types of DMA chips, concurrent
>        use of two DMA-based devices (such as diskette drive
>        and a tape controller) can result in erroneous data
>        transfers or aborted commands."
>No saying which chips, of course.  Haven't seen the problem myself. 
>As far as I know, AT&T 3.2.2 is written by ISC, so it is likely that
>this problem will appear in AT&T 386 Unix.

The AT&T 386 Unix does have the DMAEXCL parameter. Before I turned it
off, I tried installing Fastback Plus on the DOS partition of the disk.
The installation procedure includes a check for this DMA problem. My
chip passed the test, so then I turned off DMAEXCL, which is ON by
default.

Seems to me the best thing for the Colonel to do (he didn't mention
having tried it already) is to turn DMAEXCL back on and see whether this
makes the problem go away. If it does, then it's chip replacement time.
-- 
ted at eslvcr.wimsey.bc.ca   ...!ubc-cs!van-bc!eslvcr!ted    (Ted Powell)