Path: utzoo!utgpu!watserv1!watmath!att!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!wuarchive!hsdndev!husc6!genrad!decvax.dec.com!crater!paradis
From: paradis@crater.zk3.dec.com (Jim Paradis)
Newsgroups: comp.os.minix
Subject: Re: SCSI drives & ST01 interface
Keywords: SCSI ST01 AT
Message-ID: <453@decvax.decvax.dec.com.UUCP>
Date: 28 Nov 90 16:07:31 GMT
References: <1990Nov26.163451.21348@gapos.bt.co.uk>
Sender: news@decvax.dec.com.UUCP
Reply-To: paradis@crater.UUCP (Jim Paradis)
Organization: DEC ULTRIX, Nashua, NH
Lines: 46

davep@gapos.bt.co.uk (Dave Parkinson) writes:

[long story of ST01 woes deleted...]

>For now I've decided to get my extra DOS disk space from the ST01 + external
>SCSI drives, and MINIX will use the more efficient embedded AT drive.....
>
>Anyone else got any better ideas?

Well, I have a similar situation: I have a 40Mb MFM drive on my system and
an 84Mb SCSI drive hanging off an ST01.  For a short time I ran System V
on my system (386 box) and I used a driver for the ST01 that was posted to
the net sometime back.  Eventually I switched to Minix 1.5 with Bruce Evans'
32-bit patches (I'm a UNIX kernel hacker by trade and I much prefer to
run an OS that I have the sources for 8-) ).  Anyhow, eventually I decided
I wanted to access the big hard drive as well, so I started trying to hammer
that UNIX driver into MINIX.  After ripping about 80% of its guts out, I
ended up with a VERY crude driver.  It's slow (20Kb/sec with a tailwind),
and it eats up a lot of the machine, but it's also rock-solid.

I, too, had problems with the memory-mapped interface.  I solved this
by adding a couple of assembly-language routines to klib386.x which
just loaded up FLAT_DS_SELECTOR and fired away.  As for its strange
interrupt behavior... I noticed that it did not seem to want to generate
interrupts even when I supposedly had the card strapped for them.  Since
I didn't have any internals documentation and I was more interested in
getting a working driver quickly, I just ran the driver in polled mode.
Success!  Of course, when I did that, it ran slow as molasses and ate up
a ton of CPU cycles waiting for seeks... so I added a REAL hack.  Instead
of polling, I'd schedule a clock task to go off and interrupt us a couple
of ticks in the future... and I'd keep doing this until the poll succeeded.
This worked, and took up a lot less of the machine (although the CPU-driven
copy loops STILL eat up cycles like you wouldn't believe!).

It's running on my system now... these days I use the SCSI drive mainly
for archival storage and the MFM drive for working stuff.  I'd planned
to tune up the SCSI driver once I was able to get hardware docs for the
ST01, but from what you tell me it looks as though I may as well not
bother...

If anyone is interested, I'll post the driver, but I offer NO guarantees
or support.  Strictly as-is!


Jim Paradis, working at but not employed by DEC.	(603)881-1221
paradis@decvax.dec.com     			"All I got was a rock!"