From 3789398ca67aa31e5b6d4bd11097cb062bcaf117 Mon Sep 17 00:00:00 2001
From: TomW <TomW@localhost>
Date: Fri, 14 Aug 2015 21:54:42 +0100
Subject: [PATCH] Changed registers used for EGA/VGA odd/even mode.

---
 src/vid_ega.c  |  9 ++++++---
 src/vid_ega.h  |  2 +-
 src/vid_svga.c | 12 ++++++++----
 src/vid_svga.h |  2 +-
 4 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/src/vid_ega.c b/src/vid_ega.c
index d639429..a389176 100644
--- a/src/vid_ega.c
+++ b/src/vid_ega.c
@@ -77,6 +77,9 @@ void ega_out(uint16_t addr, uint8_t val, void *p)
                         ega->charsetb = (((val >> 2) & 3) * 0x10000) + 2;
                         ega->charseta = ((val & 3)        * 0x10000) + 2;
                         break;
+                        case 4:
+                        ega->chain2_write = !(val & 4);
+                        break;
                 }
                 break;
                 case 0x3ce: 
@@ -95,10 +98,10 @@ void ega_out(uint16_t addr, uint8_t val, void *p)
                         case 5: 
                         ega->writemode = val & 3;
                         ega->readmode = val & 8; 
+                        ega->chain2_read = val & 0x10;
                         break;
                         case 6:
 //                                pclog("Write mapping %02X\n", val);
-                        ega->chain2 = val & 2;
                         switch (val & 0xc)
                         {
                                 case 0x0: /*128k at A0000*/
@@ -622,7 +625,7 @@ void ega_write(uint32_t addr, uint8_t val, void *p)
         if (addr >= 0xB0000) addr &= 0x7fff;
         else                 addr &= 0xffff;
 
-        if (ega->chain2)
+        if (ega->chain2_write)
         {
                 writemask2 &= ~0xa;
                 if (addr & 1)
@@ -755,7 +758,7 @@ uint8_t ega_read(uint32_t addr, void *p)
         if (addr >= 0xb0000) addr &= 0x7fff;
         else                 addr &= 0xffff;
 
-        if (ega->chain2)
+        if (ega->chain2_read)
         {
                 readplane = (readplane & 2) | (addr & 1);
                 addr &= ~1;
diff --git a/src/vid_ega.h b/src/vid_ega.h
index fa227ae..c40190b 100644
--- a/src/vid_ega.h
+++ b/src/vid_ega.h
@@ -23,7 +23,7 @@ typedef struct ega_t
         int fast;
         uint8_t colourcompare, colournocare;
         int readmode, writemode, readplane;
-        int chain4, chain2;
+        int chain4, chain2_read, chain2_write;
         uint8_t writemask;
         uint32_t charseta, charsetb;
         
diff --git a/src/vid_svga.c b/src/vid_svga.c
index 6c0b533..2018b11 100644
--- a/src/vid_svga.c
+++ b/src/vid_svga.c
@@ -111,6 +111,7 @@ void svga_out(uint16_t addr, uint8_t val, void *p)
                                 svga->charsetb += 0x8000;
                         break;
                         case 4: 
+                        svga->chain2_write = !(val & 4);
                         svga->chain4 = val & 8;
                         svga->fast = (svga->gdcreg[8] == 0xff && !(svga->gdcreg[3] & 0x18) && !svga->gdcreg[1]) && svga->chain4;
                         break;
@@ -159,10 +160,13 @@ void svga_out(uint16_t addr, uint8_t val, void *p)
                 {
                         case 2: svga->colourcompare=val; break;
                         case 4: svga->readplane=val&3; break;
-                        case 5: svga->writemode=val&3; svga->readmode=val&8; break;
+                        case 5:
+                        svga->writemode = val & 3;
+                        svga->readmode = val & 8;
+                        svga->chain2_read = val & 0x10;
+                        break;
                         case 6:
 //                                pclog("svga_out recalcmapping %p\n", svga);
-                        svga->chain2 = val & 2;
                         if ((svga->gdcreg[6] & 0xc) != (val & 0xc))
                         {
 //                                pclog("Write mapping %02X\n", val);
@@ -741,7 +745,7 @@ void svga_write(uint32_t addr, uint8_t val, void *p)
                 writemask2=1<<(addr&3);
                 addr&=~3;
         }
-        else if (svga->chain2)
+        else if (svga->chain2_write)
         {
                 writemask2 &= ~0xa;
                 if (addr & 1)
@@ -928,7 +932,7 @@ uint8_t svga_read(uint32_t addr, void *p)
                    return 0xff;
                 return svga->vram[addr];
         }
-        else if (svga->chain2)
+        else if (svga->chain2_read)
         {
                 readplane = (readplane & 2) | (addr & 1);
                 addr &= ~1;
diff --git a/src/vid_svga.h b/src/vid_svga.h
index 141a6b3..0f514d4 100644
--- a/src/vid_svga.h
+++ b/src/vid_svga.h
@@ -31,7 +31,7 @@ typedef struct svga_t
         int fast;
         uint8_t colourcompare, colournocare;
         int readmode, writemode, readplane;
-        int chain4, chain2;
+        int chain4, chain2_write, chain2_read;
         uint8_t writemask;
         uint32_t charseta, charsetb;