Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!decwrl!sun!imagen!atari!apratt
From: apratt@atari.UUCP (Allan Pratt)
Newsgroups: comp.sys.atari.st
Subject: Re: Problem with TOS recognizing media changes
Message-ID: <1414@atari.UUCP>
Date: 28 Mar 89 23:59:08 GMT
References: <493@ultb.UUCP> <3938@druwy.ATT.COM>
Reply-To: apratt@atari.UUCP (Allan Pratt)
Organization: Atari (US) Corporation, Sunnyvale, California
Lines: 31

In article <3938@druwy.ATT.COM> dlm@druwy.ATT.COM (Dan Moore) writes:
> Unfortunately many drives do not return valid write protect
> status for several milliseconds after they are selected, which is many
> times longer than the vblank code takes.  So these drives have problems
> on the ST since media changes aren't always detected.

Another failure mode is that some drives don't give a valid
write-protect signal when there is no disk present.  This means you can
take out one write-enabled disk and put in another, and the ST won't see
a transition on the write-protect line. 

If you MUST use such a drive, have a write-protected disk handy. 
Whenever you remove a disk, place the write-protected disk in the drive
for 1 second or so, then take it out again.  In this time, the ST will
detect the transition on write-protect and mark the media as "maybe
changed." When you put in the next (write-enabled) disk, the serial
number will be read, it won't be the same, and media change processing
will commence. 

Note that going from one write-protected disk to another, the
write-protect line often doesn't change.  That's taken care of by the
floppy code, too: if the line has not changed from the write-protect
state and the last access was more than 1.5 seconds ago, the media's
state is "maybe changed."

These drives, and those mentioned by Mr.  Moore, are out of spec for the
ST: don't use them. 

============================================
Opinions expressed above do not necessarily	-- Allan Pratt, Atari Corp.
reflect those of Atari Corp. or anyone else.	  ...ames!atari!apratt