24 Mar
2007
24 Mar
'07
2:57 a.m.
Hi Chuck,
I know you don't want to do teledisk support, but having just spend
a bit of time trying your suggestion, I have one burning question...
When writing an image back to a drive, TeleDisk
doesn't really care
about anything more than the density (low or high), recording mode
(FM/MFM), and number and size of sectors. Gap computation is
performed on the basis of the drive being used to write. So declare
your drive as either a 5.25" 1.2MB or an 8" to TeleDisk and you'll be
fine, assuming your controller will write FM. Either way, the track
computation will be based on 500K data rate and a 360 RPM drive.
HOW exactly do you do this? - I admit I don't know teledisk very well,
and have never set up a custom drive table etc. however I tried to write
the image with a BIOS drive configured as a 1.2M HD - this should let
TeleDisk know it's 500kbps and 360rpm, however Teledisk refuses to try
and write it saying it's the "wrong drive type". I tried with TD2.11 and
TD2.15
As far as the 82 cylinders goes; it's the number
used for the maximum
track inspected by TeleDisk--TD will keep looking up to track 82 (or
42 for a 48 tpi drive) or (79 for an 8" drive) until no data is
returned. Some drives will hit a mechanical stop at track 80 or so,
so the positioner will just bounce against it, returning the same
data. On playback, the same thing will happen, so you'll get a valid
recreation. Things had to be this way because some copy-protected
formats use up to 42/82 cylinders; and some customers wanted to
recover manufacturing information if present (which is typically
recorded on track 40 or 80).
This gives us another clue - I was able to read the data from those
extra tracks, and 0-76 are what you would expect, 77-82 do contain
data, but are ALL exact duplicates of 76 - ie, the image WAS read on
an 8" drive (misconfigured as a 3.5"), and it "hit the stop" right
at track 77 - no extra tracks at all.
Btw - for those who want to make these disks... I was able to recreate
the disk on 8" by a round-about method. I got TeleDisk to write the
disk to a 3.5" HD drive, then used ImageDisk to read it into a .IMD
file which I could then write out to the 8" drive.
This worked, and I was able to look into the CPM 2.24 image and see
lots of strings referencing "ALTOS 64k loader" and such - so it is an
Altos disk. I was also able to read and examine the extra tracks as
noted above (IMDV is proving quite handy!)
After writing the disk with TD, TD2.11 could not read it (it locked
up requiring a hard-reset) - TD2.15 was able to re-read it. It could
also write it correctly, even though my earlier test showed that
TDCHECK from 2.15 gave bizarre side numbers. I think my final working
transfer was done with TD2.15.
The reason I did so much screwing around with TD and reading the disk
was that the first time I tried this I used the DIAG disk, and ended
up with a blank formatted disk - I was trying to verify that TD read
back the same as it wrote ... turns out that DIAG is in fact a blank
formatted disk... But at least one of the CP/M disks appear to contain
a valid boot disk image.
If anyone wants, I can use my setup to convert these to ImageDisk
format and post them to my site.
Regards,
Dave
--
dave06a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
com Collector of vintage computing equipment:
http://www.classiccmp.org/dunfield/index.html