[Coco] double-sided floppy setup in OS-9

[Robert Gault]

Chad Hendon wrote:
> Thanks for the reference to the MESS WImgTool, I tried it on my OS-9 Level 01.01.00 (1980 copyright) but kept getting errors so I decided to try the NitrOS-9.  I was impressed to learn it included its own DMODE already on the double-sided image, which booted fine.  /D1, the second drive unit, also worked as a double-sided drive by default...cool.  This is great, but I would still like the ability to do just one side or the other as /D2 or /D3 or something.  I tried setting DMODE /D2 DRIV=01 SID=01.   This worked for accessing one side of the disk only as a drive, but can't figure out what setting switches to the other side without going back to double-sided setup.
> 

It will be necessary to patch the driver to change the drive masks.

The masks are in a table that can be found by looking for
$01 $02 $04 $40
once found it needs to be changed to
$01 $41 $02 $42
Once the change is made, the drive needs to be Verified.

That should give you access to the back side of your disks even with the 
LevelI driver. /d0 and /d2 will be the front side of the disks. /d1 and 
/d3 will be the back side of the disks. The descriptors should not need 
to be changed.

You can make these changes and verify with dEd which should be on the 
NitrOS-9 distribution.