[Coco] Run NitrOS-9 on the JVC/Collyer Coco3 emulator

[Robert Gault]

Getting the NitrOS-9 images onto a real Coco system can be a problem and 
some people may want to stop on a PC with an emulator. The most 
universal emulator that can run all versions of NitrOS-9 is MESS. The 
simplest way to get the images to work with MESS is to change the 
extension from .dsk to .os9.

The latest version of the Vavasour / Collyer emulator Coco3 6309 v1.91B 
can also run NitrOS-9 with a little help. The most powerful version of 
NitrOS-9 is the Level-2 6309 and the full program is distributed on an 
80 track double sided disk image. So let's use this as an example.

The Collyer program can be obtained from RTSI
ftp://www.rtsi.com/RSDOS/incoming/  in the johncollyer_website.zip file 
as ver19.zip. Os9boot.mor (a necessary file) can be obtained at
http://www.vavasour.ca/jeff/trs80.html#coco3 . NitrOS-9 can be obtained 
from http://www.nitros9.org .

Step 1: Rename os9boot.mor to coco3.rom and install it with the 
JVC/Collyer emulator. This rom will boot directly to OS-9 using the disk 
image installed on drive0. However, one byte of the file must be changed 
with an editor so it can find the boot track on a double sided image. 
Step 2: Use a raw file editor and look for the patter $15 CC 22 01 ED 
(near the start of the file) and change the $22 to $44. Now we need to 
change the NitrOS-9 .dsk image to indicate that the disk is single sided 
instead of double sided.
Step 3: Use a raw file editor to change the 17th byte of the .dsk image 
from $03 to $02. This will tell OS-9 the image is single sided.

Now you can start the emulator and NitrOS-9 will automatically boot.

There may be one final problem with the emulator as it needs DOS not 
Windows to run NitrOS-9 correctly. Not all Windows system have a DOS 
mode. You may need to run emulation from a boot floppy on such systems.