On Thu, Nov 14, 2013 at 10:10 AM, <Ruud@baltissen.org> wrote: > Hallo Didier, > >> does anybody has an idea about the command set really issued by >> the commodore controller to the scsi hard disk ? > > I'm afraid I have some disapointments for you. > - There isn't a SCSI hard disk on board, it is a MFM one. > - Between the Commodore controller and this MFM hard disk sits a > SASI - MFM converter. Yes. One could theoretically plug in something different into the 50-pin SASI connector on the "DOS board" in place of the MFM drive and SASI-MFM bridge, but I don't recall for certain if anyone has tried it. > It is full of unknown ICs. OK, unknown to me, ISTR there are docs on the SASI-MFM board but for most of us, it's a black box (I don't _think_ there are docs handy that list all the SASI commands it recognizes). > - The Commodore controller has a SASI interface, not a SCSI one. A > German friend of mine said that SASI was the predecessor of SCSI Yes. It's "Shugart Associates System Interface" and with a few minor changes became SCSI-1. > so > one should be able to attach a SCSI hard disk. So far he hasn't > succeeded. Embedded SCSI drives came a bit after SASI was gone. Perhaps a very old 20MB drive (ST225N?) _might_ work. One issue to overcome is that the 9060/9090 uses 256-byte sectors and those sectors get written by the low-level format routines in the drive. That specifically is something that changed with different ROM revisions (I have a tech note that describes the LLF going from approx 45 min to 2 hrs when you upgrade the ROMs). I haven't disassembled the ROMs to see what they are doing there, but it would be a place to start. Having a SCSI analyzer in the chain would be *extremely* useful to watch/document the interaction. I do not have such a thing. > On the positive site: > - I made a disassembly of the ROM of Disk Controller, freely > available. > - This board does NOT use the 6530, the ROM is an EPROM in this > case. Yes. > a second solution could be to replace the EPROM by one with my own > content; not having to use this weird SASI protocol, it would > simplify the interfacing. I think it might be possible to tweak the ROM code to properly support SCSI command packets, but it would probably take a lot more tweaking to support partial sector writes to a drive that was formatted to 512 bytes per sector. The DOS 3.0 filesystem maxes out around 16MB anyway (if you were to rewrite the code that expects a ~300-cylinder drive with 32 sectors per track and either 4 or 6 heads) so there's no real loss in giving up half of each sector. Even my smallest embedded SCSI drive is 50MB, so I couldn't address every block. I still have my D9090 drives, so I do enjoy discussing ways to replace the HDAs. Mine work, but like all drives, they won't work forever. 25 years ago, I paid $100 to have one completely torn down and refurbed (it had a bad track zero sensor which is inside the sealed HDA, so since I was already paying the clean room fee, I had them replace the platters too). That drive has less than 1000 hours on it after repair. It may last a good long while, but not forever. I see two approaches to the same destination - put a SCSI bus analyzer on a working drive and watch the transactions for format, reads, and writes, and disassemble the DOS Board ROMs and look for every command packet that the board sends to the SASI-MFM board. It's probably only about half a dozen kinds. Once we know what the SASI commands are, that's a long way to sticking a replacement on the bus. -ethan Message was sent through the cbm-hackers mailing listReceived on 2013-11-14 18:00:06
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