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From: go@orstcs.UUCP
Newsgroups: comp.os.minix
Subject: Re: MINIX on the Zenith 150
Message-ID: <505100006@orstcs>
Date: Thu, 9-Apr-87 19:57:00 EST
Article-I.D.: orstcs.505100006
Posted: Thu Apr  9 19:57:00 1987
Date-Received: Sun, 12-Apr-87 01:14:48 EST
References: <129@wldrdg.UUCP>
Lines: 41
Nf-ID: #R:wldrdg.UUCP:-12900:orstcs:505100006:000:1789
Nf-From: orstcs.cs.ORST.EDU!go    Apr  9 16:57:00 1987


(I hate repeating base notes...)

This is in response to n0ano at wldrdg.UUCP regarding hard-disk promblems
on his 150 system.  I also experience the same problem on my XT clone
(uses WD 1002-WS2 controller with 20 M 225 type disk).  Reads (*lots* of
reads  MMMMEGAbytes of reads) work fine.  But sometimes when writing
the driver gets out of sync with the controller.  My theory (having
not manual for the controller -- yet) is the following:

	Driverer issues request for interrupt to occur upon
	DMA completion.  On reads, DMA completion means the
	entire transfer is complete: read from disk to controller,
	then DMA reads from controller into XT memory.

	On writes, a DMA completion simply means data has been loaded
	into controller's buffer -- disk is only then starting to
	write the data.  If another request is made for disk service
	while the data is being written to the disk, the controller
	simply won't answer.  Driver responds by resetting it and
	starting over.

Evidence collected confirms the above.  Sometimes when the errors
occur, there are blocks that haven't been written to the disk
(pieces of files are "different").

Slow speed writes never seem to cause the problem.

I was working on some attempts at fixing these problems (more like
groping in the dark without documentation on controller -- but that
is on it's way, I hope) but ran into a problem -- The system won't
run at all on the hard disk when I run the version I compile.  Note
that I haven't changed a thing except one tiny mask in the tty
driver refering to the Video Memory.  I tried simply compiling
xt_wini.c and no soap.

When I get my documentation and try a few more things, I'll be sure
to let you all know (if someone else hasn't fixed it sooner).

Gary Oliver
...!hplabs!hp-pcd!orstcs!go