Usually booting 7.5.5 doesn't reach the Finder unless you're holding the shift key during boot to disable extensions. It appears to be the same for Infinite Mac. Those DMA aborts are removed from my fork. Whatever is causing my fork to hang might be related to whatever is doing the non-DWORD read or it might be something else. It would be nice to be able to use Conflict Catcher to find the conflicting extensions, but it doesn't let you indicate pass/fail of a test during extension load time even though Conflict Catcher can appear during extension load time which is unfortunate since it can't handle conflicts that cause the Finder to be unreachable? Maybe I'm using it wrong.
The issue appears to be the Apple Photo Access extension -- disabling it both makes the non-DWORD read go away, and allows the Finder to successfully start.
The issue appears to be the Apple Photo Access extension -- disabling it both makes the non-DWORD read go away, and allows the Finder to successfully start.
Apple frequently uses multiple access widths to the SCSI controllers so you may eventually encounter non-DWORD access even without that extension. When I was bringing up the Quadras, the Control Panel was writing a block of settings from a non-word-aligned address which kicks off a bunch of lesser-used code paths in MacOS (and requires very exact 53C9x emulation to not trash the hard disk).
In this case it's reading from the DBDMA registers (which are memory-mapped), so it seems a bit unusual to read 1 byte from a word-sized register. Even if making the 1-byte read work (as joevt did in https://github.com/joevt/dingusppc/commit/3ab60e486a8b2d80b241f0e939a86ef320035631), the Finder does not finish launching (the mouse is responsive, but nothing else happens). I would guess things are going wrong earlier, and the 1-byte read is a symptom of that.