At 2005-08-14 19:44, Jens Schoenfeld wrote: >At 16:54 13.08.2005 -0800, Jaap van Ganswijk wrote: > >>Just to make sure: Does that mean that you can already >>read all the sectors from the disk? > >Yes, I can. I'm using the Catweasel floppy controller to do that, as normal >floppy controllers can't read FM disks any more.
Don't confuse the real floppy controller chip and the software. The chips still can read FM disks and by the way, MFM and FM (or DD and SD) use the same medium, but use it in a smarter manner. (And building FM into an MFM controller costs almost nothing, so they do it in the spirit of that every new PC has to be completely downwards compatible with every old PC. >These VERSAdos disks are even a weird mixture of FM and MFM sectors, with 16 >128-byte FM sectors on track 0/side 0, and 16 256-byte MFM sectors on all >other tracks. Reminds me of the Flex disk format that also used that. It would make reading the first track very fast because it could always be done quickly, because only one coding had to be tried and it would tell the OS how the rest of the disk was coded. Later they decided that old media formats shouldn't hinder progress and that it was better to try to read the first track at several formats with the most popular format of that moment first. >I haven't seen an FM-track on a 3.5" disk before, 3.5 inch disks are logically identical to 5.25 inch disks. The interface is the same and so is the formatting of the disk. 8 inch disks are different in those both respects. >and I've seen *many* disks in the past nine years. Luckily, the checksums are >all CRC-16 according to CCITT, so once I found out about the basic format, the >rest was easy. Yes, that is generally done in hardware using very old standards. >>So what you are looking for now is a way to interpret >>the file system on the disk? > >Correct. I have no clue what VARSAdos is related to - some CP/M or early DOS? >I only know that the volume name of the disk can only be 4 characters, and >that's stored in the beginning of very first sector of the disk (that is, the >first four bytes of my image file). Doesn't sound like an CPM-DOS based filesystem (like MS-DOS) but a kind of Motorola format. >Thanks for your other hints - I have also seen quite a few filesystems before, >but never really tried to hack one. One way or another, I managed to get hold >of a documentation, so I had the positions for sector pointers, directory >entries and so on. So what is the remaining problem? >>Perhaps you should make a dump of the disk contents >>and give us (or some of us) access to it? > >Sure, I can do that. Need to ask the owner of the disks first, but I guess >that's not a problem, since the disks have been formatted for this purpose. I was unclear if the disks might contain sensitive information. Analyzing newly formatted disks isn't easy however, so put some files with known content on it first. >>When the file system is very complicated, sometimes >>it is best to emulate the complete original OS on a >>modern PC and map a harddisk file as a quasi floppy >>drive. > >That's what I recommend t most of my customers, and it works fine for those >systems where an emulator exists - especially the popular ones like C64, >Amiga, Atari and Apple. However, I haven't seen an emulator for this 68K-based >realtime operating system yet, and I doubt that it really exists. Any hints >welcome...! I used to write my own emulators and writing an emulator for a processor is quite easy (once you have written a dissassembler, which is also quite easy once you have written a skeletal disassembler) but the problem is handling the hardware that the processor is connected to. BTW. I never wrote a 68000 emulator, because it has a very chaotical instruction set and it was 32-bits and I was still writing the emulators on an 8/16 bits system. (I did write a 68000-disassembler however.) Greetings, Jaap -- Author: Jaap van Ganswijk INET: [EMAIL PROTECTED] Fat City Hosting, San Diego, California -- http://www.fatcity.com --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
