From 87abbaa75eea6e1d5bcc5acd9c3afc9ba847e153 Mon Sep 17 00:00:00 2001
From: Adrian Conlon <98398945+AdrianConlon@users.noreply.github.com>
Date: Fri, 28 Mar 2025 14:50:53 +0000
Subject: [PATCH] Tidy IO page access

---
 LR35902/IoRegisters.cs |  8 ++++++--
 LR35902/LR35902.cs     | 14 ++++++++------
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/LR35902/IoRegisters.cs b/LR35902/IoRegisters.cs
index 27d0c32..d397cf4 100644
--- a/LR35902/IoRegisters.cs
+++ b/LR35902/IoRegisters.cs
@@ -8,7 +8,11 @@ namespace LR35902
 
     public sealed class IoRegisters : Ram
     {
-        public const int BASE = 0xFF00;
+        public const byte BasePage = 0xFF;
+
+        private static readonly ushort _base = Chip.PromoteByte(BasePage);
+
+        public static ushort BASE => _base;
 
         // Port/Mode Registers
         public const int P1 = 0x0;       // R/W Mask5
@@ -343,7 +347,7 @@ namespace LR35902
         private void Bus_ReadingByte(object? sender, EventArgs e)
         {
             var address = this.bus.Address.Word;
-            var io = address is >= BASE and < 0xff80;
+            var io = address >= BASE && address < 0xff80;
             if (io)
             {
                 var port = (ushort)(address - BASE);
diff --git a/LR35902/LR35902.cs b/LR35902/LR35902.cs
index b4883b1..abfcdea 100644
--- a/LR35902/LR35902.cs
+++ b/LR35902/LR35902.cs
@@ -45,10 +45,12 @@ namespace LR35902
 
         public bool IME { get; set; }
 
+        private static readonly Register16 _addressIE = new(IoRegisters.IE, IoRegisters.BasePage);
+
         public byte IE
         {
-            get => this.Bus.Peek(IoRegisters.BASE + IoRegisters.IE);
-            set => this.Bus.Poke(IoRegisters.BASE + IoRegisters.IE, value);
+            get => this.Bus.Peek(_addressIE);
+            set => this.Bus.Poke(_addressIE, value);
         }
 
         public byte IF
@@ -689,7 +691,7 @@ namespace LR35902
                                     break;
 
                                 case 4: // GB: LD (FF00 + n),A
-                                    this.MemoryWrite((ushort)(IoRegisters.BASE + this.FetchByte()), this.A);
+                                    this.MemoryWrite(this.FetchByte(), IoRegisters.BasePage, this.A);
                                     break;
 
                                 case 5:
@@ -707,7 +709,7 @@ namespace LR35902
                                     break;
 
                                 case 6: // GB: LD A,(FF00 + n)
-                                    this.A = this.MemoryRead((ushort)(IoRegisters.BASE + this.FetchByte()));
+                                    this.A = this.MemoryRead(this.FetchByte(), IoRegisters.BasePage);
                                     break;
 
                                 case 7:
@@ -772,7 +774,7 @@ namespace LR35902
                                     _ = this.JumpConditionalFlag(y);
                                     break;
                                 case 4: // GB: LD (FF00 + C),A
-                                    this.MemoryWrite((ushort)(IoRegisters.BASE + this.C), this.A);
+                                    this.MemoryWrite(this.C, IoRegisters.BasePage, this.A);
                                     break;
                                 case 5: // GB: LD (nn),A
                                     this.MEMPTR.Assign(this.FetchWord());
@@ -780,7 +782,7 @@ namespace LR35902
                                     this.MemoryWrite(this.A);
                                     break;
                                 case 6: // GB: LD A,(FF00 + C)
-                                    this.A = this.MemoryRead((ushort)(IoRegisters.BASE + this.C));
+                                    this.A = this.MemoryRead(this.C, IoRegisters.BasePage);
                                     break;
                                 case 7: // GB: LD A,(nn)
                                     this.MEMPTR.Assign(this.FetchWord());