From 8a5b552a9a43c2c65de99cdc609ed8932ff818df Mon Sep 17 00:00:00 2001
From: SarahW <pcem@pcem-emulator.co.uk>
Date: Mon, 8 Jan 2018 20:50:48 +0000
Subject: [PATCH] Correct CS:IP initialisation on 286+ reset. Patch from
 Greatpsycho.

---
 src/808x.c   | 29 ++++++++++++++++++++++++-----
 src/x86seg.c | 12 ++++++++++++
 2 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/src/808x.c b/src/808x.c
index 971367e..c761199 100644
--- a/src/808x.c
+++ b/src/808x.c
@@ -628,7 +628,6 @@ void resetx86()
         stack32=0;
 //        i86_Reset();
 //        cs=0xFFFF0;
-        cpu_state.pc=0;
         msw=0;
         if (is486)
                 cr0 = 1 << 30;
@@ -639,8 +638,18 @@ void resetx86()
         cr4 = 0;
         eflags=0;
         cgate32=0;
-        loadcs(0xFFFF);
-        rammask = AT ? 0xFFFFFFFF : 0xfffff;
+        if (AT)
+        {
+                loadcs(0xF000);
+                cpu_state.pc = 0xFFF0;
+                rammask = cpu_16bitbus ? 0xFFFFFF : 0xFFFFFFFF;
+        }
+        else
+        {
+                loadcs(0xFFFF);
+                cpu_state.pc = 0;
+                rammask = 0xfffff;
+        }
         idt.base = 0;
         flags=2;
         makeznptable();
@@ -667,13 +676,23 @@ void softresetx86()
         cpu_cur_status = 0;
 //        i86_Reset();
 //        cs=0xFFFF0;
-        cpu_state.pc=0;
         msw=0;
         cr0=0;
         cr4 = 0;
         eflags=0;
         cgate32=0;
-        loadcs(0xFFFF);
+        if (AT)
+        {
+                loadcs(0xF000);
+                cpu_state.pc = 0xFFF0;
+                rammask = cpu_16bitbus ? 0xFFFFFF : 0xFFFFFFFF;
+        }
+        else
+        {
+                loadcs(0xFFFF);
+                cpu_state.pc = 0;
+                rammask = 0xfffff;
+        }
         //rammask=0xFFFFFFFF;
         flags=2;
         idt.base = 0;
diff --git a/src/x86seg.c b/src/x86seg.c
index 87cf2c7..23d6294 100644
--- a/src/x86seg.c
+++ b/src/x86seg.c
@@ -68,6 +68,18 @@ static void seg_reset(x86seg *s)
         s->limit = 0xFFFF;
         s->limit_low = 0;
         s->limit_high = 0xffff;
+        if (s == &_cs)
+        {
+                // TODO - When the PC is reset, initialization of the CS descriptor must be like the annotated line below.
+                //s->base = AT ? (cpu_16bitbus ? 0xFF0000 : 0xFFFF0000) : 0xFFFF0;
+                s->base = AT ? 0xF0000 : 0xFFFF0;
+                s->seg = AT ? 0xF000 : 0xFFFF;
+        }
+        else
+        {
+                s->base = 0;
+                s->seg = 0;
+        }
 }
 
 void x86seg_reset()