Hi Dave
Here is another idea. Most of these machines are designed
to have multiple drives. One disconnects one of the drives
and runs the wires to a simple board on the parallel port.
That board has maybe 5 or 6 TTL's. All it does is pass
serial data from the parallel port to the read data
and possibly the read clock of the controller on the
old computer. In the PC, you configure the port to
be in the DMA mode so that it can do high speed transfers.
The board has a simple clocking from a Xtal can oscillator.
Things like single and double density are simply the bit
stream information. This is all premade in the buffer that
you are doint the DMA transfer from.
I'm not saying I've worked out all the possible problems
but I think it can be done. Things like the data rate for
5-1/4 and 8 inch can be jumper selects on the board or
maybe even encoded in the data sent.
Anyway, it needs more thought
Dwight
>From: "Dave Dunfield" <dave04a_at_dunfield.com>
>
>Hi Dan,
>
>>|With a PC format disk, and most other DD disks, I can simply issue
>>|a "read id" with the wrong data type - this times out at the index
>>|hole after two revolutions, at which point I set the right data type
>>|and perform repeated "read id"s until I see the same id again - on
>>|most disks, this quite reliably gives me the sector interleave pattern
>>|on the track.
>>|
>>|With the Cromemco disk, this does not work, as often I won't see all
>>|of the sector id's until I have reissued the "read id" many times,
>>|often seeing some sectors 30-40 times before seeing one occurance of
>>|the "tough" sectors. Clearly even if I do eventually get all the
>>|sector Id's, I cannot determine what the interleave is at all..., not
>>|to mention that this makes the "analysis stage" a but lengthy.
>>
>>Try adding an increasing small delay after the read id you use to
>>synchronize with the index hole.
>
>Yeah, I tried that earlier on with mixed results, and didn't seem to
>really get anywhere - but I've cleaned up a few other things now, so
>I'll revisit it.
>
>
>>|(read-track seems
>>|pretty useless on the 765 series).
>>
>>It is. Your best bet would be to get a 1797 family controller.
>
>Believe me, I've thought of that - problem is that I want to be able to
>send this to people to make disks - but it looks like the pee-cee controller
>(or the design) is just not up to snuff, and all I see a people having
>problems - single-density on a pc is very problematic.
>
>I've also toyed with the idea of building a very small embedded controller
>with a 1797, few tracks worth of buffer storage, and a reasonably fast serial
>link to the PC. This is basically what I am doing now to archive/restore North-
>Star disks (which are hard-sectored), except that since the N* controller
>is well defined, I can just put my code into any N* system (user supplied his
>uart routines).
>
>[or if you wanted to be super-flexible, have just a DSP - but thats a tad more
> software work than I feel like undertaking right now...]
>
>
>>|It's interesting with the Cromemco CDOS disk - the DD area is formatted
>>|to 10 512 byte sectors/track, and in the DD(360k) drive, I can't read
>>|them at all - For this test, I pulled the actual Teac drive that I have
>>|been using on the System-3 (which reads it fine) - it looks like the PC
>>|controller has touble with the tightly spaced sectors.
>>
>>It has trouble with various kinds of back-to-back operations, but I
>>wouldn't expect that to make the tracks totally unreadable. Something
>>else is going on. Is it possible that the BIOS thinks you have an
>>80 track drive and is double-stepping? That would let you read track
>>0 but no other.
>
>I'm not using BIOS at all - I'm communcating directly with the FDC and
>DMA controller. It simply does not see Sector-1 on the SD track, almost
>all the time!
>
>
>>|It (the DD drive) can however read all of the SD sectors in track-0
>>|just fine!
>>|
>>|The HD drive reads the entire disk perfectly, EXCEPT for Sector-1 of
>>|Track-0 (the SD track) - it quite reliably refuses to read the first
>>|sector of the SD track. The remaining sectors of the SD track and all
>>|of the DD tracks read OK.
>>
>>Try covering the index hole cutout on the disk or otherwise blocking the
>>drive's index sensor. The controller does not like to start a read too
>>close to the index hole, but it will mostly work without any index pulses.
>>(It won't format or timeout of course.)
>
>Interesting idea - I'll give that a try, at least it might shed some more
>light on what exactly is going on.
>
>
>Regards,
>Dave
>--
>dave04a (at) Dave Dunfield
>dunfield (dot) Firmware development services & tools: www.dunfield.com
>com Collector of vintage computing equipment:
> http://www.parse.com/~ddunfield/museum/index.html
>
>
>
Received on Mon Feb 21 2005 - 19:42:48 GMT