FramebufferWC

FramebufferWC improves VBE framebuffer performance on OPENSTEP 4.2 x86.

It has two parts:

• The driver configures the framebuffer as write-combining with an MTRR.
• The VBE patch tells WindowServer to use a copy-back framebuffer mapping.

Both are needed for full WindowServer performance. The stock VBE driver sets no cache-policy flag, so DriverKit defaults to a slow write-through mapping. The patch preserves the gamma flag and adds IO_DISPLAY_CACHE_COPYBACK for the active display and its mode list. It does not change the video mode, framebuffer address, pixel format, or display hardware.

On a test machine, full-screen drawing improved from about 171 ms/frame to 0.85-1.17 ms/frame.

Build

cd /path/to/FramebufferWC
PATH=/usr/ucb:/bin:/usr/bin make clean all

The result is FramebufferWC.config. It includes the optional framebufferwc-control and vbe-cache-patch utilities.

Install

Copy FramebufferWC.config to /private/Drivers/i386/ and make it owned by root.wheel.

Add the driver immediately after VBE in /private/Drivers/i386/System.config/Instance0.table:

... VBE20DisplayDriver FramebufferWC ...

Check and patch the stock VBE driver:

/private/Drivers/i386/FramebufferWC.config/vbe-cache-patch status
su
/private/Drivers/i386/FramebufferWC.config/vbe-cache-patch patch
/usr/etc/reboot

The patcher accepts only the exact known stock OPENSTEP 4.2 VBE binary. It creates and verifies VBE20DisplayDriver_reloc.stock, refuses to overwrite an existing backup, installs through a temporary file, and verifies the result. Unknown or partly modified binaries are refused.

A successful boot registers Display0 followed by FramebufferWC0.

Runtime control

/private/Drivers/i386/FramebufferWC.config/framebufferwc-control status
su
/private/Drivers/i386/FramebufferWC.config/framebufferwc-control off
/private/Drivers/i386/FramebufferWC.config/framebufferwc-control on

off restores the MTRR entries captured when the driver loaded. It does not remove the VBE patch.

Restore the stock VBE driver

su
/private/Drivers/i386/FramebufferWC.config/vbe-cache-patch restore
/usr/etc/reboot