CV64VBlankHack

Short:        Makes VBLANK work on CyberVision64
Author:       Martin Blom (lcs@lysator.liu.se)
Uploader:     Martin Blom (lcs lysator liu se)
Type:         driver/video
Architecture: m68k-amigaos

The first thing I noticed when I got my CV64 last year was that the 
Workbench icons flickered a lot when I moved them.

This is because CyberGraphX cannot handle VBLANK interrupts. This means
that many functions in graphics.library are broken (VBeamPos(), WaitBOVP()
and WaitTOF() for example).

This program is a hack that solves this problem. It uses timer.device to
simulate VBLANK interrupts at the correct frequency, and also syncronizes
the interrupts with the vertical retrace bit found in all VGA chips. In
addition to that, it uses the E clock to calculate which scan line the
raster beam is at.

Sounds good? It isn't. timer.device seem to have too much overhead for this
usage. The solution is to use a CIA level 6 timer interrupt instead. I
wont do that, but feel free to do it yourself - the source is included.

The program can only be used with CyberVision64, but it should be simple to
make it work with other graphic cards, since all use VGA compatible chips.

The program and source is public domain.