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VBL Fix v1.0 — G4 mini OS 9 startup-freeze fix

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@UnexpectedBomb UnexpectedBomb released this 01 Jul 14:28
v1.0
dd268a0

What this fixes: the intermittent frozen-cursor startup hang on a G4 Mac mini running Mac OS 9 at a non-native (scaled) resolution. The Radeon 9200 (ATY,Bee) driver leaves the display's VBL interrupt disabled after the boot-time mode switch; this re-arms it.

Which file to use:

  • VBLFix_v1.img — the fix. Silent everyday version: drop VBL Fix into System Folder → Startup Items.
  • VBLAutofix_v1.img — tester build (reports via beep + log), for confirming results.

.img are Apple Partition Map disk images that mount on OS 9 with resource forks intact (recommended); .bin are MacBinary equivalents.

Status: working fix, seeking testers — the freeze is intermittent (~5% of boots), so broad testing across machines is how we build confidence. See the README for the test protocol and TECHNICAL.md for the root cause.

Caveat: this fixes the common case (frozen cursor). A rare, more severe variant (garbled screen / hard hang right at the switch) happens too early for any app to catch — native resolution remains the only fully-robust mode.

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