[Coco] Vcc+DW4 to access real floppy drive on Coco-3 ?

[Gene Heskett]

On Monday 07 July 2014 23:27:54 Kandur did opine
And Gene did reply:
> Thanks Gene.
> 
> Kandur
> 
> Monday, July 7, 2014, 11:10:29 AM, you wrote:
> > On Monday 07 July 2014 11:59:29 Kandur did opine
> > 
> > And Gene did reply:
> >> Bill, what I wanted was, to access physical floppy drives on the
> >> Coco, while running Nitro OS-9 on VCC. Drive ON/OFF don't seem to
> >> work on the Coco's physical drives from OS-9.
> >> 
> >> Kandur
> > 
> > That is because in nitros9, HDBDOS is not used and there are two
> > different descriptor "families".  You configure the bootfile to
> > include the proper /D0, /D1, or /D2 for the physical drives, but you
> > have to configure /SH to access the virtual drives.  If you have the
> > drive space beyond the end of the os9 "partition", then /SH,
> > configured correctly, can access any virtual disk, in however many
> > groups of 255 that you have room for on the hard drive.
> > 
> > You have to dmode 3 variables in the descriptor to do this.
> > 
> > The "stp", range $00 to $ff selects the vdisk within the group.
> > wpc (1 hex byte) and ofs (hex int) are to be used to point at the
> > first sector of each group of 255 virtual disks.  So on my main hard
> > drive, /SH is currently set to look at the $80th, or 128th, disk in
> > group 0, whose address in wpc=1D and ofs=BB90.  Leave the dollar
> > sign out of the dmode command though, its not needed.
> > 
> > Each additional group is done by adding to the $1D,BB90, the number
> > of sectors that 256 disks of 35 track, 18 sectors per track that a
> > single sided disk image would occupy.  The next group(1) then would
> > have a starting sector of $1DBB90 + $27600=$20,3190.
> > 
> > Repeat, adding $27600 each time until out of drive space. ;-)
> > 
> > I hope this helps.
> > 
> > Cheers, Gene Heskett

One thing I perhaps didn't detail well enough, is that the $1DBB90 used 
above, is from my main drive, which has about 500 megs for nitros9, 
leaving about 500 megs for virtual disks.  Your hard drive quite likely 
will have a different size recorded in its LSN0 at DD_SIZ.

I have 2 identical 1Gb seagate Hawk scsi-ii drives, the second one is 
formatted all nitros9.  That goes over the clusters demarcation twice, so 
while the main drive functions with a 4 sectors per bit in the FAT, the 
2nd drive uses one bit in the FAT to represent 16 sectors.  Its odd, but a 
1 byte file then blocks out 16 sectors for that one byte file.  With a 
gigabyte to wander around in, its not really a problem as the files size, 
and the amount of disk it allocates, are two different things.

Cheers, Gene Heskett
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