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From: neals@tekigm.UUCP (Neal Sedell)
Newsgroups: net.micro.6809
Subject: Re: Disk level CRC
Message-ID: <600@tekigm.UUCP>
Date: Thu, 24-Oct-85 13:56:01 EDT
Article-I.D.: tekigm.600
Posted: Thu Oct 24 13:56:01 1985
Date-Received: Fri, 25-Oct-85 09:18:07 EDT
References: <867@lsuc.UUCP>
Distribution: na
Organization: Tektronix, Beaverton OR
Lines: 38

> All I can say is, I've had
> corrupted files load and execute under Radio Shack DOS and not
> on OS-9.

   I have had this problem too.  I only use BASIC so I can load a game.
I transferred it from casette to disk for convenience.  At first it
loaded and ran every time.  Then, all of a sudden, it loads, the startup
screen comes on and then nothing.  I use the disk so infrequently that I
don't recall if I wrote to it in the interim.  This is really frustrating
because it should be IMPOSSIBLE to load a bad sector.  When one is
found the disk retrys the read and reseeks several times.
Since the file loads without any reseeking we can conclude that the
sector was re-written with the wrong data on it an thus was "good" in
the eyes of the loader.  Does anyone know what is "wrong" with Disk
BASIC?  I don't read Rainbow or Hot COCO so if anyone does or knows
of a bug with file allocation could they please tell us about it?
Could it be a problem with the SAVEM command?  The file was of
the default type .BIN, and I would assume James O's program was too,
not that one has anything to do with the other.

   Speaking of OS9 and CRC's, these are only present in LOADable files
(executable and device descriptors), not in text files.  I think the
only reason they are there is for the mentioned software in silicon
concept in order to absolutely distinguish a random bit pattern from
a module at boot time.  You might see the header in RAM but the odds
of the CRC being right is about the same as a snowball's chance in....

   BTW, I have gotten "read error"s but never a "bad CRC" message
when trying to execute an OS9 program (except when I had edited some
of its bytes and forgotten to "verify -u" it to fix the CRC).  File
level CRC will detect file corruption as in paragraph 1, but only for
LOADable files.

   I sure wish the time necessary for CRC verification was insignificant!


			Neal Sedell
			...!tektronix!neals