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Nov 6, 2024 at 17:15 comment added dirkt @cjs it's not only the varying number (which wouldn't matter if everything was consecutive, though skew handling becomes difficult), it also skips areas that having meaning in the CBM format. As I wrote, irregular.
Nov 6, 2024 at 4:49 comment added cjs "...some irregular mapping of CP/M blocks to tracks/sectors..." Oh, of course! Because the CBM GCR formats have a varying number of sectors per track, depending on how close the track is to the centre of the diskette.
Nov 6, 2024 at 4:43 comment added cjs "Leaving this answer here nevertheless for information." It's very useful information that can save time-wasting experimentation for people looking to solve the main problem, so I've updated the question such that this is now a direct answer to (part of) it. Thanks for doing the experimentation!
Nov 5, 2024 at 21:28 comment added john_e If I were in that position, I'd write a libdsk driver that presented the .D64 / .D71 (etc) file as a raw disk image containing only the sectors used by CP/M, and then have cpmtools access it through libdsk.
Nov 5, 2024 at 20:43 comment added Craig Estey @cjs If the Commodore file system format is problematic, another way to develop programs may be to use qemu (which has some z80 emulation addons (of varying quality)) to boot the Commodore's CP/M OS. This might be more work initially (if the z80 emul doesn't support basic Commodore physical devices) but gives a possible fallback approach if all else fails.
Nov 5, 2024 at 13:08 comment added cjs I believe several images are available from this page. Having had a (very) quick look at ctools source code, I am suspecting that the format may be a combination of CBM and CP/M, because I thought I saw it updating a block address map.
Nov 5, 2024 at 13:01 history edited dirkt CC BY-SA 4.0
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Nov 5, 2024 at 11:52 comment added dirkt That's why I wrote "I don't know how well this will work". It looks like D71 is a "raw" format, so one could probably add some entry there, if the Commodore CP/M layout is documented somewhere. If you can put a D71 file online somewhere I can give it a try.
Nov 5, 2024 at 11:17 comment added cjs I looked at cpmtools and saw no entry for any Commodore formats in the diskdefs file.
Nov 5, 2024 at 7:05 history answered dirkt CC BY-SA 4.0