[CDG5] ATI frozen mouse bug, cross-post from MacOS9Lives

[Elliot Nunn]

I have fixed the frozen mouse bug!

It was, as darthnVader hinted earlier, caused by the ATI extensions. So I took a
deep dive into the ATI driver architecture. This is the typical "life cycle" of
an ATI card in a NewWorld Mac:

1.  If the card firmware lacks an ndrv (e.g. the Radeon 9200 in the mini), the
    MacOS uses its generic "COFB" ndrv to get basic video.
2.  Extensions are loaded from disk. The ATI ROM Xtender or iMic's hacked "ATI
    Via Driver" extension can replace the previously loaded ndrv. No graphical
    acceleration yet.
3.  The complex array of ATI extensions steps in, asks the loaded ndrv about the
    card using some private Status calls, and loads some acceleration code if the
    card is recognised. Accelerated 2D requires "ATI Resource Manager" and "ATI
    Graphics Accelerator" at minimum.

This was darthnVader's solution to get graphics acceleration working:

1.  Insert a Mac OS X ndrv into iMic "ATI Via Driver" (better called "ATI
    RockHopper2 Driver" after the change).
2.  Replace all or most occurrences of the 5961 device ID in the other extensions
    with 5962. Both IDs refer to the Radeon 9200, but the extensions only knew about
    the 5961 ID. (Occurrences of 5960 were also replaced -- see below.)

DarthnVader effectively turned our minis into Mac OS 9 gaming rigs!
Unfortunately, one of the binary patches intermittently broke hardware cursor
support. It might be due to the way that the PowerPC compiler optimised
select/case blocks. Sometimes I also experienced a black screen when the ATI
extensions loaded, which I think was related.

This is my solution:

1.  Insert the same Mac OS X ndrv (ATY,RockHopper2 v1.0.1f63, from Mac OS X
    10.3.6) into the Mac OS ROM as an ndrv parcel, to mimic a firmware driver.

2.  Patch that ndrv to replace 5962 with 5961 whenever it reads from PCI
    Configuration Space.
    - To achieve this, I got sidetracked and wrote a single-file PowerPC assembler
      script (ppcasm.py) and PEF dump/rebuild script (cfmtool.py):
      https://github.com/elliotnunn/tbxi-patches/

3.  Use the unmodified ATI extensions from January 2005.
    - The extensions that we host in "9200os9.sit", supposedly from the rare July
      2005 release, do not work.
    - I think that they were binary-patched to enable support for the DVI-I Radeon
      9200 card, ID 5960. Specifically, the accl 4 resource of the "ATI Graphics
      Accelerator" is an identical build to January 2005, including the build
      date, but has 2/2 occurrences of 5961 replaced with 5960. It would be good
      to find the originals.

So here is my first ROM release of the year. It was derived from the
"OS9General" Mac OS ROM (v9.6.1) using my portable Mac mini patching system:
https://github.com/elliotnunn/tbxi-patches/blob/7a5d179/macmini.py

My ATALoad patch has also been applied, to allow Mac OS 9 to boot from volumes
that were formatted for Mac OS X, without first wiping the disk with "Mac OS 9
Drivers". I think that this is especially useful on machines that were formerly
Mac OS X-only.

I recommend that this ROM be included in a new release of the Mac mini ISO. It
should be combined with the unmodified ATI extensions from January 2005.