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

[Gene Heskett]

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
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