diff --git a/src/Bus.zig b/src/Bus.zig
index 72add6d..a1eec70 100644
--- a/src/Bus.zig
+++ b/src/Bus.zig
@@ -125,6 +125,7 @@ pub fn write16(self: *Self, addr: u32, halfword: u16) void {
         0x0500_0000...0x05FF_FFFF => self.ppu.palette.set16(addr & 0x3FF, halfword),
         0x0600_0000...0x0601_7FFF => self.ppu.vram.set16(addr - 0x0600_0000, halfword),
         0x0700_0000...0x07FF_FFFF => self.ppu.oam.set16(addr & 0x3FF, halfword),
+        0x0800_00C4, 0x0800_00C6, 0x0800_00C8 => log.warn("Tried to write 0x{X:0>4} to GPIO", .{halfword}),
 
         else => undWrite("Tried to write 0x{X:0>4} to 0x{X:0>8}", .{ halfword, addr }),
     }
diff --git a/src/apu.zig b/src/apu.zig
index 840a248..854db35 100644
--- a/src/apu.zig
+++ b/src/apu.zig
@@ -43,6 +43,10 @@ pub const Apu = struct {
         self.ch_vol_cnt.raw = (self.ch_vol_cnt.raw & 0xFF00) | byte;
     }
 
+    pub fn setSoundCntLHigh(self: *Self, byte: u8) void {
+        self.ch_vol_cnt.raw = @as(u16, byte) << 8 | (self.ch_vol_cnt.raw & 0xFF);
+    }
+
     pub fn setBiasHigh(self: *Self, byte: u8) void {
         self.bias.raw = (@as(u16, byte) << 8) | (self.bias.raw & 0xFF);
     }
@@ -51,9 +55,13 @@ pub const Apu = struct {
 const ToneSweep = struct {
     const Self = @This();
 
+    /// NR10
     sweep: io.Sweep,
+    /// NR11
     duty: io.Duty,
+    /// NR12
     envelope: io.Envelope,
+    /// NR13, NR14
     freq: io.Frequency,
 
     fn init() Self {
@@ -65,6 +73,10 @@ const ToneSweep = struct {
         };
     }
 
+    pub fn setFreqLow(self: *Self, byte: u8) void {
+        self.freq.raw = (self.freq.raw & 0xFF00) | byte;
+    }
+
     pub fn setFreqHigh(self: *Self, byte: u8) void {
         self.freq.raw = (@as(u16, byte) << 8) | (self.freq.raw & 0xFF);
     }
@@ -73,8 +85,11 @@ const ToneSweep = struct {
 const Tone = struct {
     const Self = @This();
 
+    /// NR21
     duty: io.Duty,
+    /// NR22
     envelope: io.Envelope,
+    /// NR23, NR24
     freq: io.Frequency,
 
     fn init() Self {
@@ -85,8 +100,12 @@ const Tone = struct {
         };
     }
 
+    pub fn setFreqLow(self: *Self, byte: u8) void {
+        self.freq.raw = (self.freq.raw & 0xFF00) | byte;
+    }
+
     pub fn setFreqHigh(self: *Self, byte: u8) void {
-        self.freq.raw = (self.freq.raw & 0x00FF) | (@as(u16, byte) << 8);
+        self.freq.raw = @as(u16, byte) << 8 | (self.freq.raw & 0xFF);
     }
 };
 
@@ -94,10 +113,13 @@ const Wave = struct {
     const Self = @This();
 
     /// Write-only
+    /// NR30
     select: io.WaveSelect,
     /// NR31    
     length: u8,
+    /// NR32
     vol: io.WaveVolume,
+    /// NR33, NR34
     freq: io.Frequency,
 
     fn init() Self {
@@ -108,6 +130,14 @@ const Wave = struct {
             .length = 0,
         };
     }
+
+    pub fn setFreqLow(self: *Self, byte: u8) void {
+        self.freq.raw = (self.freq.raw & 0xFF00) | byte;
+    }
+
+    pub fn setFreqHigh(self: *Self, byte: u8) void {
+        self.freq.raw = @as(u16, byte) << 8 | (self.freq.raw & 0xFF);
+    }
 };
 
 const Noise = struct {
@@ -116,8 +146,11 @@ const Noise = struct {
     /// Write-only
     /// NR41
     len: u6,
+    /// NR42
     envelope: io.Envelope,
+    /// NR43
     poly: io.PolyCounter,
+    /// NR44
     cnt: io.NoiseControl,
 
     fn init() Self {
diff --git a/src/bus/io.zig b/src/bus/io.zig
index b3ff351..b365004 100644
--- a/src/bus/io.zig
+++ b/src/bus/io.zig
@@ -124,6 +124,9 @@ pub fn read16(bus: *const Bus, addr: u32) u16 {
         // Sound
         0x0400_0088 => bus.apu.bias.raw,
 
+        // DMA Transfers
+        0x0400_00BA => bus.dma._0.cnt.raw,
+
         // Timers
         0x0400_0100 => bus.tim._0.counter(),
         0x0400_0102 => bus.tim._0.cnt.raw,
@@ -221,6 +224,8 @@ pub fn write16(bus: *Bus, addr: u32, halfword: u16) void {
 
         // Serial Communication 2
         0x0400_0134 => log.warn("Wrote 0x{X:0>4} to RCNT", .{halfword}),
+        0x0400_0140 => log.warn("Wrote 0x{X:0>4} to JOYCNT", .{halfword}),
+        0x0400_0158 => log.warn("Wrote 0x{X:0>4} to JOYSTAT", .{halfword}),
 
         // Interrupts
         0x0400_0200 => bus.io.ie.raw = halfword,
@@ -239,6 +244,13 @@ pub fn read8(bus: *const Bus, addr: u32) u8 {
         0x0400_0006 => @truncate(u8, bus.ppu.vcount.raw),
 
         // Sound
+        0x0400_0060 => bus.apu.ch1.sweep.raw,
+        0x0400_0063 => bus.apu.ch1.envelope.raw,
+        0x0400_0069 => bus.apu.ch2.envelope.raw,
+        0x0400_0073 => bus.apu.ch3.vol.raw,
+        0x0400_0079 => bus.apu.ch4.envelope.raw,
+        0x0400_007C => bus.apu.ch4.poly.raw,
+        0x0400_0081 => @truncate(u8, bus.apu.ch_vol_cnt.raw >> 8),
         0x0400_0089 => @truncate(u8, bus.apu.bias.raw >> 8),
 
         // Serial Communication 1
@@ -258,14 +270,26 @@ pub fn write8(bus: *Bus, addr: u32, byte: u8) void {
         0x0400_0005 => bus.ppu.dispstat.raw = (@as(u16, byte) << 8) | (bus.ppu.dispstat.raw & 0xFF),
 
         // Sound
+        0x0400_0060 => bus.apu.ch1.sweep.raw = byte,
+        0x0400_0062 => bus.apu.ch1.duty.raw = byte,
         0x0400_0063 => bus.apu.ch1.envelope.raw = byte,
+        0x0400_0064 => bus.apu.ch1.setFreqLow(byte),
         0x0400_0065 => bus.apu.ch1.setFreqHigh(byte),
+        0x0400_0068 => bus.apu.ch2.duty.raw = byte,
         0x0400_0069 => bus.apu.ch2.envelope.raw = byte,
+        0x0400_006C => bus.apu.ch2.setFreqLow(byte),
         0x0400_006D => bus.apu.ch2.setFreqHigh(byte),
         0x0400_0070 => bus.apu.ch3.select.raw = byte,
+        0x0400_0072 => bus.apu.ch3.length = byte,
+        0x0400_0073 => bus.apu.ch3.vol.raw = byte,
+        0x0400_0074 => bus.apu.ch3.setFreqLow(byte),
+        0x0400_0075 => bus.apu.ch3.setFreqHigh(byte),
+        0x0400_0078 => bus.apu.ch4.len = @truncate(u6, byte),
         0x0400_0079 => bus.apu.ch4.envelope.raw = byte,
+        0x0400_007C => bus.apu.ch4.poly.raw = byte,
         0x0400_007D => bus.apu.ch4.cnt.raw = byte,
         0x0400_0080 => bus.apu.setSoundCntLLow(byte),
+        0x0400_0081 => bus.apu.setSoundCntLHigh(byte),
         0x0400_0084 => bus.apu.setSoundCntX(byte >> 7 & 1 == 1),
         0x0400_0089 => bus.apu.setBiasHigh(byte),