'Index hole sensor in 1571'
Author:Nate (guest: search)
Date: Sun, Mar 22nd, 2009 @ 13:06 ( . )

Hi guys. I did add an IHS to my 1541 and patched mnib to support it. I sent the listing to Pete with comments on how to add more general support to mnib for this. Here is a duplicate of those comments:

Yes, I used the UU method of hooking the IR LED up to the same line as
the status LED. Then you just reconfigure it for input instead of output
and read it. Bit 7 of 1c00 will go low when the hole passes. You can
find the schematic in one version of the SuperCard disks.

Attached is the diff I made to mnib to use it. It may have bugs but
hopefully it will help. I think you only want to make the pin input
while using the IHS since otherwise the LED won't work for status. Also,
I considered adding a diode to prevent current flowing into the VIA but
it turned out it would not forward bias correctly so I never used it. It
turns out to not be a problem.

I think there are several steps to adding IHS support to mnib. First,
add a flag to mnib to enable the IHS at runtime. I just used an ifdef.
Also, add a separate test function to be sure the IHS is working
(similar to "cbmctrl detect"). Next, create a new flag in the header
area for .nib files to indicate that the data in these tracks is
synchronized. That way we can tell if a .nib file was made with IHS
enabled or not.

When creating an image with IHS enabled, mnib can just bump the head,
wait for IHS detected, then begin reading. This way every track in the
.nib file starts from the same location. Write support can work the same
way (wait for IHS, then begin writing). By doing this, the new disk will
match the old. Also, the .nib file will be synchronized properly for use
with emulators if they honor the flag in the header or keep the sync the
same as in the .g64 file.

My ultimate goal was to use the hardware IHS to test various
signature-based synchronization schemes like Womo built in order to work
without an IHS. Then, all newer versions of mnib would set the
"track-synchronized" .nib header bit if they were able to successfully
detect the skew.

Such software-only schemes might have a hard time for tracks that had
only a small amount of data and all sync, for example. If the track just
before the key track for RapidLok disks (t35) had little data, it might
be hard to detect the skew for the key track.


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--* Index hole sensor in 1571
3/22/2009 @ 14:21--Pete Rittwage

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