[Coco] Important Announcement: NitrOS-9 & 1986 GIME

[Robert Gault]

This is a message for everyone who is unable to run NitrOS-9 on a Coco3 
with a 1986 GIME chip.

As background, there are two versions of the GIME, 1986 & 1987. The '86 
chip was the cause for many articles on "sparklies" that plagued early 
adopters of the Coco3. There were also problems with the verticle and 
horizontal scroll registers. I just found out that it is next to 
impossible to boot NitrOS-9 (any version) on an '86 GIME Coco3.

There are several theories that try to explain this problem and present 
ways to correct it. To date, none have been successful during my testing 
of the problem. The short story is that there are mistakes in the 
circuits of the '86 GIME that can't handle the stress of NitrOS-9 code. 
The strange aspect of this problem is that occasionally the boot process 
completes and NitrOS-9 then runs without problems.

I have found a workaround that seems to give 100% success at booting 
NitrOS-9 on an '86 GIME Coco3. Change the boot screen from 40 or 80 
character width to 32. You can still boot to an 80 character wide /term 
as this has no effect on stability. The boot screen is still in a Coco3 
video mode rather than Coco1, so why this works is still a mystery.

                         !!!HOW TO DO IT!!!
It is only necessary to change one byte in sector 1 of track 34 to get a 
successful boot. This changes the module REL. Once booted, you can 
os9gen a fresh boot disk from the current NitrOS-9 release using the 
rel_32 module if desired. Using the new module will then have the 
NITROS9 BOOT
   (FAILED)
message in the correct location on the screen. The one byte patch will 
prevent the message from printing, although the diagnostics will still 
be readable.

Using either a PC disk editor, an OS-9 disk editor (dEd), or one for 
Disk Basic, locate in T34S1 the bytes $6C 00 00 00 09 00 00 00 '0B or 
03' and '34 or 24'. It is the last byte in this sequence, $34 or $24, 
that needs to be changed to $20. You don't need to bother with the crc 
bytes and once booted you ought to create a new boot disk with a proper 
rel_32 module.

If you don't have a disk editor for Disk Basic, you can manage the same 
thing with DSKI$ and DSKO$