From 74793aaf9985816c330819759af4f7f0c6bbcd61 Mon Sep 17 00:00:00 2001
From: TomW <TomW@localhost>
Date: Sun, 15 Dec 2013 14:29:52 +0000
Subject: [PATCH] Mach64 now disables VGA data processing on LFB writes.
 Windows 9x DOS boxes now rendered correctly.

---
 src/vid_ati_mach64.c | 6 +++++-
 src/vid_svga.c       | 8 ++++----
 src/vid_svga.h       | 2 ++
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/vid_ati_mach64.c b/src/vid_ati_mach64.c
index e06a1cd..b65b2be 100644
--- a/src/vid_ati_mach64.c
+++ b/src/vid_ati_mach64.c
@@ -630,7 +630,7 @@ void mach64_blit(uint32_t cpu_dat, int count, mach64_t *mach64)
                         int mix;
                         int dst_x = mach64->accel.dst_x + mach64->accel.dst_x_start;
                         int dst_y = mach64->accel.dst_y + mach64->accel.dst_y_start;
-                
+
                         if (mach64->accel.source_host)
                         {
                                 host_dat = cpu_dat;
@@ -1291,6 +1291,10 @@ void mach64_ext_writeb(uint32_t addr, uint8_t val, void *p)
 
                 case 0x1c: case 0x1d: case 0x1e: case 0x1f:
                 WRITE8(addr, mach64->crtc_gen_cntl, val);
+                if (((mach64->crtc_gen_cntl >> 24) & 3) == 3)
+                        svga->fb_only = 1;
+                else
+                        svga->fb_only = 0;
                 svga_recalctimings(&mach64->svga);
                 break;
 
diff --git a/src/vid_svga.c b/src/vid_svga.c
index d27d635..0a9f2b7 100644
--- a/src/vid_svga.c
+++ b/src/vid_svga.c
@@ -660,7 +660,7 @@ void svga_write(uint32_t addr, uint8_t val, void *p)
         addr += svga->write_bank;
 
         if (!(svga->gdcreg[6] & 1)) svga->fullchange=2;
-        if (svga->chain4)
+        if (svga->chain4 || svga->fb_only)
         {
                 writemask2=1<<(addr&3);
                 addr&=~3;
@@ -836,7 +836,7 @@ uint8_t svga_read(uint32_t addr, void *p)
 
 //        pclog("%05X %i %04X:%04X %02X %02X %i\n",addr,svga->chain4,CS,pc, vram[addr & 0x7fffff], vram[(addr << 2) & 0x7fffff], svga->readmode);
 //        pclog("%i\n", svga->readmode);
-        if (svga->chain4) 
+        if (svga->chain4 || svga->fb_only) 
         { 
                 addr &= 0x7fffff;
                 if (addr >= svga->vram_limit)
@@ -888,7 +888,7 @@ void svga_write_linear(uint32_t addr, uint8_t val, void *p)
         if (svga_output) pclog("Write LFB %08X %02X ", addr, val);
         if (!(svga->gdcreg[6] & 1)) 
                 svga->fullchange = 2;
-        if (svga->chain4)
+        if (svga->chain4 || svga->fb_only)
         {
                 writemask2=1<<(addr&3);
                 addr&=~3;
@@ -1057,7 +1057,7 @@ uint8_t svga_read_linear(uint32_t addr, void *p)
 
         egareads++;
         
-        if (svga->chain4) 
+        if (svga->chain4 || svga->fb_only) 
         { 
                 addr &= 0x7fffff;
                 if (addr >= svga->vram_limit)
diff --git a/src/vid_svga.h b/src/vid_svga.h
index f969abd..405a187 100644
--- a/src/vid_svga.h
+++ b/src/vid_svga.h
@@ -25,6 +25,8 @@ typedef struct svga_t
         
         uint8_t plane_mask;
         
+        int fb_only;
+        
         int fast;
         uint8_t colourcompare, colournocare;
         int readmode, writemode, readplane;