Miller's Graphics Advanced Diagnostic (TI-99/4a) protection?

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SomeGuy
Posts: 252
Joined: Wed Feb 18, 2015 8:18 pm

Miller's Graphics Advanced Diagnostic (TI-99/4a) protection?

Post by SomeGuy »

I dumped a Miller's Graphics Advanced Diagnostics disk that is intended to be used with their CorComp 9900 floppy disk controller, but it has a number of "bad" sectors on it. It has some wacky copy protection on it - part of disk uses different sized sectors and track numbering. The disk is clean and seems to be in good physical condition, so I'm not sure if these are really bad sectors on tracks 7, 8 and 9, or if this is perhaps part of their odd copy protection. I don't have a functional CorComp floppy controller to test with.

Just looking at the tracks plotted out, it looks like either damage or a spot of degaussing.

Here is the dump if anyone wants to look at it:
http://s000.tinyupload.com/?file_id=806 ... 4560216183

brightcaster
Posts: 249
Joined: Fri Nov 08, 2013 10:48 pm

Re: Miller's Graphics Advanced Diagnostic (TI-99/4a) protection?

Post by brightcaster »

If it looks like a spot I would look for a spot of mould on the disks surface first of all. Especially because the tracks affected are closed to eatch other! The mold spot lifts tuhe head and gives bad reading at that area.

Cleaning the spot may give you 100% correct sectors imediantly! I experienced this verry often, espessially with 5,25" floppies. For cleaning I only used destilled water and "Q-Tip"....

Regards, David

SomeGuy
Posts: 252
Joined: Wed Feb 18, 2015 8:18 pm

Re: Miller's Graphics Advanced Diagnostic (TI-99/4a) protection?

Post by SomeGuy »

Actually, I had already cleaned the disk and I re-cleaned it several times just to be sure. Also didn't have any better luck with other drives. It must be some small bit of physical damage I can't quite see.

rcade
Posts: 121
Joined: Mon Nov 21, 2011 5:21 pm

Re: Miller's Graphics Advanced Diagnostic (TI-99/4a) protection?

Post by rcade »

Have to look and see if the disk protection checks this area. On the few I've seen with physical damage, the protection usually tries to write to the disk in the bad spot. If it is successful, it is a copy.
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Pete Rittwage
C64 Preservation Project
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IFW
Posts: 3079
Joined: Mon Nov 08, 2010 2:42 pm

Re: Miller's Graphics Advanced Diagnostic (TI-99/4a) protection?

Post by IFW »

Actually, it could be either.
On track 6 and 7 it is a small unformatted (weak bit) or damaged area.
Track 8 however looks like damage.
Attachments
Track 8
Track 8
Track 6
Track 6

SomeGuy
Posts: 252
Joined: Wed Feb 18, 2015 8:18 pm

Re: Miller's Graphics Advanced Diagnostic (TI-99/4a) protection?

Post by SomeGuy »

I did some more analysis on this disk. Only the first bad sector (track 6 sector 6) contains actual data, and only a few bytes in the sector are affected. Since the contents are a simple text file, it is easy to extrapolate the contents should be:

Code: Select all

00000000  13 53 44 20 32 20 43 57-20 35 30 34 20 33 36 20    .SD 2 CW 504 36 
00000010  5B 31 33 5D 13 53 44 20-31 20 43 52 20 35 34 30    [13].SD 1 CR 540
00000020  20 33 36 20 5B 31 33 5D-13 53 44 20 32 20 43 57     36 [13].SD 2 CW
00000030  20 35 34 30 20 33 36 20-5B 31 33 5D 13 53 44 20     540 36 [13].SD 
00000040  31 20 43 52 20 35 37 36-20 33 36 20 5B 31 33 5D    1 CR 576 36 [13]
00000050  13 53 44 20 32 20 43 57-20 35 37 36 20 33 36 20    .SD 2 CW 576 36 
00000060  5B 31 33 5D 13 53 44 20-31 20 43 52 20 36 31 32    [13].SD 1 CR 612
00000070  20 33 36 20 5B 31 33 5D-13 53 44 20 32 20 43 57     36 [13].SD 2 CW
00000080  20 36 31 32 20 33 36 20-5B 31 33 5D 13 53 44 20     612 36 [13].SD 
00000090  31 20 43 52 20 36 34 38-20 33 36 20 5B 31 33 5D    1 CR 648 36 [13]
000000A0  13 53 44 20 32 20 43 57-20 36 34 38 20 33 36 20    .SD 2 CW 648 36 
000000B0  5B 31 33 5D 13 53 44 20-31 20 43 52 20 36 38 34    [13].SD 1 CR 684
000000C0  20 33 36 20 5B 31 33 5D-13 53 44 20 32 20 43 57     36 [13].SD 2 CW
000000D0  20 36 38 34 20 33 36 20-5B 31 33 5D 13 53 44 20     684 36 [13].SD 
000000E0  31 20 43 52 20 37 32 30-20 33 36 20 5B 31 33 5D    1 CR 720 36 [13]
000000F0  FF 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00    ................
But wow, this disk contains all kinds of goofiness. The first 26 tracks (0-25) all contain an unused sector #42. Otherwise these are normal TI-99/4a single density 256 byte sectors.

Then Tracks 26-38 use 512 byte sectors. Not only do they use odd sector numbering, but also intentionally incorrect track IDs.

Then track 39 has three 1024 byte sectors, and the last sector appears intentionally truncated (you can't fit three 1024 byte sectors on an SD track).

And finally, all of the tracks seem a bit too long and appear to cross the index boundary a bit at the end. ImageDisk would not read the last sector on most tracks. I'm surprised that works on a TI.

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