VBL Fix v2.0 — Classic-safe

v2 — community-validated, now Classic-safe.

Since v1, the fix has been confirmed rock-solid on multiple G4 minis — one tester ran 30+ restart cycles with zero freezes, and toggling it off brought the freezing right back (thanks to the testers on the MacOS9Lives thread).

New in v2: a guard so the fix cleanly no-ops under the Classic environment (Mac OS X). It fixes a hang reported when booting an OS 9 partition via Classic on Tiger — under Classic the display is virtualized and the enable call has no real hardware to drive. On native OS 9 nothing changes: the guard can only skip the fix under Classic, never suppress it on real hardware, so v2 is a safe drop-in over v1 for everyone.

Which file:

• VBLFix_v2.img — the fix (silent everyday version). Drop VBLFix_v2 into System Folder → Startup Items.
• VBLAutofix_v2.img — tester build (beep + log).

.img disk images preserve the Mac resource forks (recommended); .bin are MacBinary equivalents. Native behavior is unchanged from the validated v1 — the v1.0 release is still there if you want the previous build.

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

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.