From c75682dbd45f30834f7e3efb3493a3a4bb4f3a98 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Sat, 29 Oct 2022 04:29:44 -0300
Subject: [PATCH] fix(apu): some invalid i/o registers should read 0x0000

---
 src/core/apu.zig | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/src/core/apu.zig b/src/core/apu.zig
index 0d8afe2..d95f387 100644
--- a/src/core/apu.zig
+++ b/src/core/apu.zig
@@ -48,25 +48,26 @@ pub fn read(comptime T: type, apu: *const Apu, addr: u32) ?T {
             0x60 => apu.ch1.sound1CntL(),
             0x62 => apu.ch1.sound1CntH(),
             0x64 => apu.ch1.sound1CntX(),
-            0x66 => null,
+            0x66 => 0x0000, // suite.gba expects 0x0000, not 0xDEAD
             0x68 => apu.ch2.sound2CntL(),
-            0x6A => null,
+            0x6A => 0x0000,
             0x6C => apu.ch2.sound2CntH(),
-            0x6E => null,
+            0x6E => 0x0000,
             0x70 => apu.ch3.sound3CntL(),
             0x72 => apu.ch3.sound3CntH(),
             0x74 => apu.ch3.sound3CntX(),
-            0x76 => null,
+            0x76 => 0x0000,
             0x78 => apu.ch4.sound4CntL(),
-            0x7A => null,
+            0x7A => 0x0000,
             0x7C => apu.ch4.sound4CntH(),
-            0x7E => null,
+            0x7E => 0x0000,
             0x80 => apu.soundCntL(),
             0x82 => apu.soundCntH(),
             0x84 => apu.soundCntX(),
-            0x86 => null,
+            0x86 => 0x0000,
             0x88 => apu.bias.raw, // SOUNDBIAS
-            0x8A, 0x8C, 0x8E => null,
+            0x8A => 0x0000,
+            0x8C, 0x8E => null,
             0x90, 0x92, 0x94, 0x96, 0x98, 0x9A, 0x9C, 0x9E => apu.ch3.wave_dev.read(T, apu.ch3.select, addr),
             0xA0, 0xA2 => null, // FIFO_A
             0xA4, 0xA6 => null, // FIFO_B
@@ -76,25 +77,26 @@ pub fn read(comptime T: type, apu: *const Apu, addr: u32) ?T {
             0x60, 0x61 => @truncate(T, @as(u16, apu.ch1.sound1CntL()) >> shift(byte)),
             0x62, 0x63 => @truncate(T, apu.ch1.sound1CntH() >> shift(byte)),
             0x64, 0x65 => @truncate(T, apu.ch1.sound1CntX() >> shift(byte)),
-            0x66, 0x67 => null,
+            0x66, 0x67 => 0x00, // assuming behaviour is identical to that of 16-bit reads
             0x68, 0x69 => @truncate(T, apu.ch2.sound2CntL() >> shift(byte)),
-            0x6A, 0x6B => null,
+            0x6A, 0x6B => 0x00,
             0x6C, 0x6D => @truncate(T, apu.ch2.sound2CntH() >> shift(byte)),
-            0x6E, 0x6F => null,
+            0x6E, 0x6F => 0x00,
             0x70, 0x71 => @truncate(T, @as(u16, apu.ch3.sound3CntL()) >> shift(byte)), // SOUND3CNT_L
             0x72, 0x73 => @truncate(T, apu.ch3.sound3CntH() >> shift(byte)),
             0x74, 0x75 => @truncate(T, apu.ch3.sound3CntX() >> shift(byte)), // SOUND3CNT_L
-            0x76, 0x77 => null,
+            0x76, 0x77 => 0x00,
             0x78, 0x79 => @truncate(T, apu.ch4.sound4CntL() >> shift(byte)),
-            0x7A, 0x7B => null,
+            0x7A, 0x7B => 0x00,
             0x7C, 0x7D => @truncate(T, apu.ch4.sound4CntH() >> shift(byte)),
-            0x7E, 0x7F => null,
+            0x7E, 0x7F => 0x00,
             0x80, 0x81 => @truncate(T, apu.soundCntL() >> shift(byte)), // SOUNDCNT_L
             0x82, 0x83 => @truncate(T, apu.soundCntH() >> shift(byte)), // SOUNDCNT_H
             0x84, 0x85 => @truncate(T, @as(u16, apu.soundCntX()) >> shift(byte)),
-            0x86, 0x87 => null,
+            0x86, 0x87 => 0x00,
             0x88, 0x89 => @truncate(T, apu.bias.raw >> shift(byte)), // SOUNDBIAS
-            0x8A...0x8F => null,
+            0x8A, 0x8B => 0x00,
+            0x8C...0x8F => null,
             0x90...0x9F => apu.ch3.wave_dev.read(T, apu.ch3.select, addr),
             0xA0, 0xA1, 0xA2, 0xA3 => null, // FIFO_A
             0xA4, 0xA5, 0xA6, 0xA7 => null, // FIFO_B