From ac78275cb831d8cf4ffb3e0dc49142862e794200 Mon Sep 17 00:00:00 2001
From: OBattler <oubattler@gmail.com>
Date: Wed, 24 Jan 2024 20:45:44 +0100
Subject: [PATCH] EGA: Correct register (non-)readability on the Compaq EGA and
 light pen registers.

---
 src/include/86box/vid_ega.h |  2 ++
 src/video/vid_ega.c         | 33 ++++++++++++++++++++-------------
 2 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/src/include/86box/vid_ega.h b/src/include/86box/vid_ega.h
index ec241d613..0bccd607e 100644
--- a/src/include/86box/vid_ega.h
+++ b/src/include/86box/vid_ega.h
@@ -56,6 +56,8 @@ typedef struct ega_t {
 
     uint8_t *vram;
 
+    uint16_t light_pen;
+
     int vidclock;
     int fast;
     int extvram;
diff --git a/src/video/vid_ega.c b/src/video/vid_ega.c
index 7979cd958..dd84074e6 100644
--- a/src/video/vid_ega.c
+++ b/src/video/vid_ega.c
@@ -295,22 +295,22 @@ ega_in(uint16_t addr, void *priv)
             break;
 
         case 0x3c0:
-            if (ega_type)
+            if (ega_type == 1)
                 ret = ega->attraddr | ega->attr_palette_enable;
             break;
         case 0x3c1:
-            if (ega_type)
+            if (ega_type == 1)
                 ret = ega->attrregs[ega->attraddr];
             break;
         case 0x3c2:
             ret = (egaswitches & (8 >> egaswitchread)) ? 0x10 : 0x00;
             break;
         case 0x3c4:
-            if (ega_type)
+            if (ega_type == 1)
                 ret = ega->seqaddr;
             break;
         case 0x3c5:
-            if (ega_type)
+            if (ega_type == 1)
                 ret = ega->seqregs[ega->seqaddr & 0xf];
             break;
         case 0x3c6:
@@ -318,24 +318,24 @@ ega_in(uint16_t addr, void *priv)
                 ret = ega->ctl_mode;
             break;
         case 0x3c8:
-            if (ega_type)
+            if (ega_type == 1)
                 ret = 2;
             break;
         case 0x3cc:
-            if (ega_type)
+            if (ega_type == 1)
                 ret = ega->miscout;
             break;
         case 0x3ce:
-            if (ega_type)
+            if (ega_type == 1)
                 ret = ega->gdcaddr;
             break;
         case 0x3cf:
-            if (ega_type)
+            if (ega_type == 1)
                 ret = ega->gdcreg[ega->gdcaddr & 0xf];
             break;
         case 0x3d0:
         case 0x3d4:
-            if (ega_type)
+            if (ega_type == 1)
                 ret = ega->crtcreg;
             break;
         case 0x3d1:
@@ -349,14 +349,21 @@ ega_in(uint16_t addr, void *priv)
                     break;
 
                 case 0x10:
-                case 0x11:
-                    /* TODO: Return light pen address once implemented. */
-                    if (ega_type)
+                    if (ega_type == 1)
                         ret = ega->crtc[ega->crtcreg];
+                    else
+                        ret = ega->light_pen >> 8;
+                    break;
+
+                case 0x11:
+                    if (ega_type == 1)
+                        ret = ega->crtc[ega->crtcreg];
+                    else
+                        ret = ega->light_pen & 0xff;
                     break;
 
                 default:
-                    if (ega_type)
+                    if (ega_type == 1)
                         ret = ega->crtc[ega->crtcreg];
                     break;
             }