Xref: utzoo comp.unix.wizards:6639 comp.sys.dec:535
Path: utzoo!mnetor!uunet!husc6!cmcl2!brl-adm!umd5!trantor.umd.edu!chris
From: chris@trantor.umd.edu (Chris Torek)
Newsgroups: comp.unix.wizards,comp.sys.dec
Subject: Re: TM78 (TU78) question: Read Opposite operation
Message-ID: <2338@umd5.umd.edu>
Date: 22 Feb 88 20:00:25 GMT
References: <2323@umd5.umd.edu> <10102@ulysses.homer.nj.att.com>
Sender: ris@umd5.umd.edu
Reply-To: chris@trantor.umd.edu (Chris Torek)
Organization: University of Maryland, College Park
Lines: 34

>In article <2323@umd5.umd.edu> I asked:
>>Is the 4.3BSD [TU78] driver wrong once or twice?

It appears I insulted the driver unnecessarily.  I have yet to find
a bug here, but...

In article <10102@ulysses.homer.nj.att.com> ggs@ulysses.homer.nj.att.com
(Griff Smith) writes:
>The driver, as released in 4.3BSD, does have a few bugs - not in error
>recovery that I know of.

... I spotted a nice bug in mtustart, for cooked devices (not that
anyone uses these, but I was trying to figure out why we got these
duplicates, and this code does seek).  At the bottom it does something
like

	if (x < y)
		count = y - x;
	else
		count = x - y;
	if (count > 0377)
		count = 0377;
	mtaddr->mtncs[MUUNIT(bp->b_dev)] = count | MT_SFORW | MT_GO;

which will only ever space forward.  Hm.

>... The "read opposite" refers to the sense of the original
>command, not to that of the retry.

The TM78 User's Guide is rather ambiguous, but does imply this.
-- 
In-Real-Life: Chris Torek, Univ of MD Computer Science, +1 301 454 7163
(hiding out on trantor.umd.edu until mimsy is reassembled in its new home)
Domain: chris@mimsy.umd.edu		Path: not easily reachable