[Coco] Copying over an IO ERROR

[Arthur Flexser]

I wonder if anyone has ever written a read-track based CoCo disk zapper for
recovering damaged data.  I would envision something that would read the
desired track and use some smart algorithms to try to intelligently guess
where the sector boundaries lie, allowing the user to modify these in some
user-friendly fashion (e.g., using the arrow keys to adjust the boundaries
of a 256-byte region and edit bytes within there) and save a copy of the
modified sector.
(I seem to remember hearing, from an author of Spit N Image, that the read
track command is a little twitchy, so that you don't always get exactly the
same result if you use it twice in a row.)

One problem is that you can't just do a read track, modify a bit of data,
and save it back out with a write track.  There are a few byte values that
the write track command uses for things like "generate a CRC here" that
mess you up if you happen to have one of these bytes in the data that the
disk contains.  So saving would have to be by means of sector, not track,
writes.

Art

On Tue, Feb 3, 2015 at 8:34 PM, John Riddle <jcriddle74 at gmail.com> wrote:

> Hi,
> I keep forgetting to mention this, but one thing you could try doing to see
> if you can recover any data on a track with bad sectors is to read the full
> track image using the disk controller's "READ TRACK" command.  IIRC there
> is a program called "READTRAK.BIN" on Sportsware's Super Disk.  I went
> ahead and checked and it is in fact in the Coco Archive, in the
> Disks/Utilities subdir.. the manual is too, in
> Documents/Manuals/Utilities.  Basically what it does is read the track
> image in, which includes all of the data that describes the layout of the
> track and the sector data itself.  The problem is, however, that that
> utility doesn't allow for saving anything back to disk.  Now that I'm
> thinking about it, I remember Tim Lindner wrote a utility to read in track
> 0 on Diecom's protected disks - utilizing the READ TRACK controller command
> - no reason why that couldn't be used to read in a regular track and take a
> look.  You'd even be able to easily modify it to save back to disk any
> recoverable data.
> I think that the Coco DSKCON disk I/O routines in Disk Basic will error out
> with an I/O error on anything wrong at all with the sector on the track
> (which could be caused by a number of different issues, even the sector
> data being one byte off causing the CRC check to fail).
> John
>
> On Tue, Feb 3, 2015 at 7:09 PM, Allen Huffman <alsplace at pobox.com> wrote:
>
> > > On Feb 3, 2015, at 6:01 PM, Bill <cwgordon at carolina.rr.com> wrote:
> > >
> > > By using a modified version of what Allen showed me, I've been able to
> > get all (but one) of the 1984 Rainbow on Tapes onto a .DSK image.
> > >
> > > Now only a hundred or so to go <grin>
> >
> >
> > Now — the gotcha is any bad sectors are skipped, and if they had data,
> you
> > end up with files that are missing inside. I made mine write out a sector
> > of “******”s for bad sectors, so later I could identify which 256-byte
> > blocks of data were gone.
> >
> > I also had a second version that copied all the files using the COPY
> > command instead of sectors. I knew some disks might only give me one shot
> > and then I could never read them again, so I started with a
> > sector-by-sector copy. Then, if there was an error, I would do a second
> > attempt just getting files — an easy way to identify which file was bad.
> >
> > I have things I have lost forever, but fortunately, my RGB-DOS hard drive
> > platter has backups of most of my floppies back then — including one
> disk I
> > was terribly sad to see missing (custom graphics I did for a Houston Boat
> > Show for my father, when I had first gotten the CoCo 3).
> >
> > Lots of gotchas along the way — but at least I have most of the files I
> > wanted saved. Most, anyway.
> >
> > --
> > Allen Huffman - PO Box 22031 - Clive IA 50325 - 515-999-0227 (vmail/TXT
> > only)
> > Sub-Etha Software - http://www.subethasoftware.com - Established 1990!
> > Sent from my MacBook.
> >
> > P.S. Since 4/15/14, I have earned OVER $600  in Amazon gift cards via
> > Swagbucks! Use my link and I get credit:
> > http://swagbucks.com/refer/allenhuffman
> >
> >
> >
> >
> >
> >
> > --
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> >
>
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