#338 Fixed 64k address wrap for 320x200x8 when CGA comp. mode set

[reg2s]

I had problem with video scrolling in Titan game in 320x200x8 mode (ax=000Dh, int 10h). Game works perfect on real machine (GeForce 2 mx400 videocard). But in dosbox if bit 0 of CRTC register is set to 0 (CGA compatible address mode on) video memory address isn't wrap at 64k.
Problem can be fixed with this patch (VGA_SetupDrawing() function -> switch (vga.mode) -> case M_EGA:).

[reg2s]

[Qbix]

according to h-a-l-9000 this bug has been fixed

[Qbix]

sorry mis understood something

[Qbix]

sorry mis understood something

[reg2s]

Screenshots from original dosbox-0.73 and from patched one

[reg2s]

Excuse me for my english and for bad explanation of problem.

Dosbox doesn't react to this code:

mov dx, 3D4h ; Video: CRT cntrlr addr
mov al, 17h ; register index 17h
out dx, al
inc dx
mov al, 0E2h ;bit 0 is set to 0
out dx, al ;(CGA compatible address mode on)

On real videocard this code leads to video memory address wrap at 64k boundary and game works. I've attached zip-archive with screenshots made in original dosbox-0.73 and in patched one.

[h-a-l-9000]

Attaching a diff of how I'd fix this issue. It's a part of how real hardware does it.

An occasional black line remains in the game with both solutions. Probably because wrapping in a line isn't supported.

[h-a-l-9000]

No idea how to add files - so I'll add it here:

Index: src/hardware/vga_draw.cpp

RCS file: /cvsroot/dosbox/dosbox/src/hardware/vga_draw.cpp,v
retrieving revision 1.111
diff -u -r1.111 vga_draw.cpp
--- src/hardware/vga_draw.cpp 10 Sep 2009 17:44:57 -0000 1.111
+++ src/hardware/vga_draw.cpp 24 Oct 2009 14:52:11 -0000
@@ -800,6 +805,8 @@
#endif
switch (vga.mode) {
case M_EGA:
+ if (!(vga.crtc.mode_control&0x1)) vga.draw.linear_mask &= ~0x10000;
+ else vga.draw.linear_mask |= 0x10000;
case M_LIN4:
vga.draw.byte_panning_shift = 8;
vga.draw.address += vga.draw.bytes_skip;

[reg2s]

Thank you very much for your reply. Your fix is more accurate. I tried it and game works fine.

BTW, occasional black line disappear if those new lines would be

• if (!(vga.crtc.mode_control&0x1)) vga.draw.linear_mask &= 0xffff;
• else vga.draw.linear_mask |= 0x10000;

[Qbix]

The bug has been fixed.
Wait for the upcoming new version to see it.

Or:

The updated source is available by cvs.

See the link on top of the screen for information on how to get
the new sources.

The DOSBox Team