|author||Matthew Ogilvie <firstname.lastname@example.org>||2012-08-23 00:24:42 -0600|
|committer||malc <email@example.com>||2012-08-24 07:44:39 +0400|
vga: add some optional CGA compatibility hacks
This patch adds some optional compatibility hacks (default disabled) to allow Microport UNIX to function under qemu. I've tried to structure it to be easy to add more hacks for other old CGA programs, if anyone ever needs them. Microport UNIX System V/386 v 2.1 (ca 1987) tries to program the CGA registers directly with neither the assistance of BIOS, nor with proper handling of EGA/VGA-only registers. Note that it didn't work on real VGA hardware, either (although in that case, the most obvious problems seemed to be out-of-range hsync and/or vsync signalling, rather than the issues in this patch). Eventually real MDA and/or CGA support might provide an alternative to this patch, although a hybrid approach like this patch might still be useful in marginal cases. Signed-off-by: Matthew Ogilvie <firstname.lastname@example.org> Signed-off-by: malc <email@example.com>
Diffstat (limited to 'qemu-options.hx')
1 files changed, 19 insertions, 0 deletions
diff --git a/qemu-options.hx b/qemu-options.hx
index 3e8085d463..0682338e9f 100644
@@ -975,6 +975,25 @@ Valid optional properties are
Select dumb (default) or precise VGA retrace logic, useful for some
+Enable various extra CGA compatibility hacks for programs that are
+trying to directly set CGA modes without BIOS assistance nor
+real knowledge of EGA/VGA. These might only work with -vga std.
+Valid hacks are
+Wait to blank the screen until palette registers seem to actually be
+modified, instead of blanking it as soon as the palette address bit (0x10)
+of the attribute address register (0x3c0) is cleared.
+Ignore attempts to change the VGA font height (index 9),
+cursor start (index 10), and cursor end (index 11) of the CRTC control
+registers (0x3d5) if trying to set them to the default for CGA fonts
+instead of VGA fonts.
+Enable all CGA hacks. More CGA hacks may be added in future versions