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Path: utzoo!mnetor!uunet!husc6!purdue!umd5!trantor.umd.edu!chris
From: chris@trantor.umd.edu (Chris Torek)
Newsgroups: comp.unix.wizards,comp.sys.dec
Subject: TM78 (TU78) question: Read Opposite operation
Message-ID: <2323@umd5.umd.edu>
Date: 19 Feb 88 12:39:29 GMT
Sender: ris@umd5.umd.edu
Reply-To: chris@trantor.umd.edu (Chris Torek)
Organization: University of Maryland, College Park
Lines: 18

The TM78 User's Guide says that the proper response to a Read
Opposite is to issue another read command using the opposite of
the previous direction (forward if the last was a read reverse;
reverse otherwise).  The 4.3BSD driver simply does a read reverse.
Probably it is wrong.  It seems, however, that after one, or perhaps
several, read reverse operations, the driver winds up re-reading
a previously read block.

So the question:  Is the 4.3BSD driver wrong once or twice?  That
is, is there some reason to ignore the advice in the TM78 User's
Guide, or to believe that a Read Opposite will only occur once per
transfer? In addition, is it necessary to issue a Forward Record
operation after a successful reverse read, or will the controller
do this automatically?
-- 
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