[Coco] Booting original OS-9 Level 1 v1.0 or 1.1 on CoCo3

[David Gettle]

I actually have a version of level1 that will boot on a coco3 without an
issue, as well as the config system for it. I think it was uploaded to the
CoCo OS-9 archive.But, I don't remember the file name.


On Sat, Oct 8, 2022 at 5:24 PM Robert "Exile In Paradise" Murphey via Coco <
coco at maltedmedia.com> wrote:

> OS-9 Level I v1.0 and v1.1 will crash/hang if you boot a CoCo 3 with
> them.
>
> The OS9 BOOT screen appears, and then you're stuck until power down or
> reset.
>
> This happens when the RELocate code overwrites the CoCo 3's extra IRQ
> vectors stored by Super Extended BASIC in $FE00 - $FEFF
>
> Since OS-9 is Position Independent Code (PIC), all we need to do is
> patch the RELocate code to move the loaded kernel modules down one page
> from $F000 to $EF00 to avoid overwriting the CoCo 3 vectors.
>
> This is how OS-9 Level I v2.0 avoids locking up on boot on a CoCo3.
>
> HOW-TO
> Open the OS9L1V1M.DSK with a hex editor
> Go to offset 0x26400 which is the first sector of the track 34 boot
> track.
>
> Patch 1: Patch the REL relocation destination address from $F000 to
> $EF00
> Look for F0 00 around offset 0x26441
> Change the F0 to EF
>
> Patch 2: Patch REL's jump into the relocated OS9 kernel after it's
> moved to $EF00.
> Look for F0 56 around offset 0x26455
> Change the F0 to EF
>
> Patch 3: Patch the COLD10 routine's CMPX $F000 to $EF00
> Look for F0 00 around offset 0x2651A
> Change the F0 to EF
>
> Save and boot!
>
> Alternatively you could put Robert Gault's O9L1PAT.BAS on a floppy and
> use a dual floppy system to let it run and make the changes above to
> the OS9L1V1M.DSK system master disk loaded as a second floppy.
>
> http://aaronwolfe.com/robert.gault/Coco/Downloads/O9L1PAT.BAS
>
> --
> Robert "Exile In Paradise" Murphey <exile at weylan-yutani.com>
> Weylan-Yutani Corporation
>
>
> --
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