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toinet
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Inscrit le: 15 Juin 2007
Messages: 2886
Localisation: Le Chesnay, France
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 Posté le: Dim 21 Aoû 2016, 22:24 Sujet du message: Snooper troops v1 (Spinnaker, 1983) |
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#908 - This is an eduware. This is a detective game. In the Snooper troops series, several titles were published, this one is the first of the series.
Disk structure
This is a nearly standard DOS 3.3 disk: volume 254, 35 tracks of 16 sectors. Markers have been changed in the address field in the epilog markers:
For tracks 0 to 2:
- Address field: D5AA96 EDAA instead of D5AA96 DEAA
For tracks 3 to $22 except track 9
- Address field: BBAA96 EDAA instead of D5AA96 DEAA
For track 9: we have data, the track is formatted but the data is non standard. That smells like a nibble count or a nibble check.
How to copy
Launch my copy disk, use Advanced demuffin 1.4
| Code: |
Enter the monitor:
B930:18 60 EA
B98B:18 60 EA to skip the epilog marker checks
Press control-Y to return
Format a blank disk in drive 2
Insert the original disk in drive 1
Copy T0-T2
Enter the monitor
B955:BB
Press control-Y to return
Copy T3-T8
Copy TA-T22
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Let's normalize
Boot my copy disk, launch DiskFixer 4
| Code: |
T0/S3/91: ED -> DE
T0/C/84: 4C B4 BB -> AD E9 B7
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Some sort of boot trace
We tried to search for the C9 BB or A9 BB sequence, one that would change the first address field marker value from D5 to BB but we found none. So, we analyzed the pseudo DOS 3.3 boot code. The T0/S0 loads the RWTS. The RWTS loads the DOS 3.3 and control is given to $9D84.
At $9D84 we usually find a LDA $B7E9 to get the slot number but here we found a JMP $BBB4. So, we analyzed the code at $BBB4 and found out code was moved, decyphered and executed to check the nibbles of track 9.
So, the easy patch was to replace the JMP $BBB4 with the usual LDA $B7E9. We tried again and it worked! Therefore, we did no disassembly, we were happy!
The disk image is available at http://www.brutaldeluxe.fr/crack/
Reboot and... enjoy,
LoGo
8/2016 |
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