[Coco] Imaging MM/1 Floppy Disks

[Joel Ewy]

On 12/31/2015 04:58 PM, Joel Ewy wrote:
> I'm trying to image some MM/1 floppy disks, and not having any success 
> yet.  The Toolshed documentation suggests using setfdprm from the 
> fdutils package to configure /dev/fdX for a CoCo floppy disk.  In the 
> example, it uses a preset definition:  coco40ds which I can't find 
> anymore.  In any case, the MM/1 format is different. However, using 
> the documentation here: http://www.fdutils.linux.lu/Fdutils.html#SEC22 
> I came up with a plausible setfdprm command:
>
> sudo setfdprm sect=33 hd ssize=256 cyl=80.
>
> The syntax seems to be accepted.  This page: 
> http://www.fdutils.linux.lu/disk-id.html suggests that one should then 
> be able to use
>
> cat /dev/fd0 >image.dsk
>
> to write the image file.  When I try this, it fails with an 
> Input/Output error, writing 0 bytes to the file.  I also tried
>
> dd if=/dev/fd0 of=image.dsk bs=256
>
> and got the same results.  I tried two different disks and got the 
> same results.  The first one I tried is a freshly formatted, 
> previously unused disk that I backed up a boot floppy onto on the MM/1 
> with no error reported on the backup.  When I did the backup, it first 
> complained that the formats weren't identical.  A vague recollection 
> returned that the boot disks were formatted to 33 sectors, while the 
> device descriptors for /d0 and /d1 are set for 37 sectors.  Presumably 
> the boot ROM expects 33 sector disks. There is a floppy disk format 
> table in the MM/1 Technical Manual that describes the MM/1 format as 
> 33 sectors.  So I used dmode to change the sct and t0s to 33, and 
> reformatted the floppy.  Then backup was happy to copy the disk.
>
> The drive I'm using to try to make the image can read a FAT formatted 
> floppy that I can also read on the MM/1, so I'm pretty confident it 
> isn't a hardware issue.
>
> Any ideas what I'm doing wrong?
>
> JCE
>
>
I think part of the problem lies in the fact that the MM/1 disks use a 
sector offset (starting sector number) of 0.  I was able to image a CoCo 
720K floppy with no problem, and it starts at sector 1.  So I used dmode 
on the MM/1 to format a floppy disk that was identical to the MM/1's 
usual format, with the exception that soffs=1.  I copied a bunch of 
files onto it with dsave.  I was able to create an image file from this 
disk, and Toolshed's os9 dir command did show the root directory of the 
disk.  But when I looked in the CMDS directory, the first half of the 
contents showed up fine, but the rest of the directory listing was 
garbled.  os9 dcheck showed that the file system is corrupted.  But on 
the MM/1, dcheck gives a clean bill of health to the physical disk.

I notice that every time I try to read a high density MM/1 floppy, 
formatted to either 33 or 37 sectors per track, dd goes through the 
motions, and creates an image file, but also gives an I/O error at the 
end.  Also, it consistently reports that it has copied 160 sectors fewer 
than the disk format should have -- with either 33 or 37 spt, and 
apparently with soffs=0 or soffs=1.  160 sectors is 2 sectors per track 
on an 80 track disk.

JCE