diff --git a/src/apu/dmc.rs b/src/apu/dmc.rs
index 504e182..57e1b75 100644
--- a/src/apu/dmc.rs
+++ b/src/apu/dmc.rs
@@ -1,6 +1,14 @@
-impl super::DMC {
+pub struct DMC {
+    pub sample: u16,
+    pub enabled: bool,
+    pub interrupt: bool,
+    pub length_counter: usize,
+    pub bytes_remaining: usize,
+}
+
+impl DMC {
     pub fn new() -> Self {
-        super::DMC {
+        DMC {
             sample: 0,
             enabled: false,
             bytes_remaining: 0,
diff --git a/src/apu/mod.rs b/src/apu/mod.rs
index be1e492..9bfb431 100644
--- a/src/apu/mod.rs
+++ b/src/apu/mod.rs
@@ -3,6 +3,11 @@ mod square;
 mod triangle;
 mod dmc;
 
+use noise::Noise;
+use square::Square;
+use triangle::Triangle;
+use dmc::DMC;
+
 // APU clock ticks every other CPU cycle.
 // Frame counter only ticks every 3728.5 APU ticks, and in audio frames of 4 or 5.
 // Length counter controls note durations.
@@ -33,48 +38,6 @@ pub struct Apu {
     frame_interrupt: bool,
 }
 
-struct Square {
-    sample: u16,
-    duty_cycle: u8,
-    length_counter_halt: bool, // (this bit is also the envelope's loop flag)
-    constant_volume_flag: bool, // (0: use volume from envelope; 1: use constant volume)
-    timer: usize,
-    length_counter: usize,
-    envelope: usize,
-    sweep: usize,
-    enabled: bool,
-}
-
-// $4008 	Hlll.llll 	Triangle channel length counter halt and linear counter load (write)
-// bit 7 	H--- ---- 	Halt length counter (this bit is also the linear counter's control flag) 
-struct Triangle {
-    sample: u16,
-    timer: usize,
-    length_counter: usize, // (this bit is also the linear counter's control flag) 
-    linear_counter: usize,
-    enabled: bool,
-}
-
-// $400E 	M---.PPPP 	Mode and period (write)
-// bit 7 	M--- ---- 	Mode flag 
-struct Noise {
-    sample: u16,
-    timer: usize,
-    length_counter: usize,
-    envelope: usize,
-    linear_feedback_sr: u16,
-    mode: bool, // also called loop noise, bit 7 of $400E
-    enabled: bool,
-}
-
-struct DMC {
-    sample: u16,
-    enabled: bool,
-    interrupt: bool,
-    length_counter: usize,
-    bytes_remaining: usize,
-}
-
 struct Envelope {
     start_flag: bool,
     divider: usize,
diff --git a/src/apu/noise.rs b/src/apu/noise.rs
index bc00cfa..a7a3870 100644
--- a/src/apu/noise.rs
+++ b/src/apu/noise.rs
@@ -1,6 +1,19 @@
-impl super::Noise {
+
+// $400E 	M---.PPPP 	Mode and period (write)
+// bit 7 	M--- ---- 	Mode flag 
+pub struct Noise {
+    pub sample: u16,
+    timer: usize,
+    pub length_counter: usize,
+    envelope: usize,
+    linear_feedback_sr: u16,
+    mode: bool, // also called loop noise, bit 7 of $400E
+    pub enabled: bool,
+}
+
+impl Noise {
     pub fn new() -> Self {
-        super::Noise {
+        Noise {
             timer: 0,
             length_counter: 0,
             envelope: 0,
diff --git a/src/apu/square.rs b/src/apu/square.rs
index 40c8dda..699f5fc 100644
--- a/src/apu/square.rs
+++ b/src/apu/square.rs
@@ -1,7 +1,28 @@
-impl super::Square {
+const duty_cycle_sequences: [[u8; 8]; 4] = [
+    [0, 1, 0, 0, 0, 0, 0, 0],
+    [0, 1, 1, 0, 0, 0, 0, 0],
+    [0, 1, 1, 1, 1, 0, 0, 0],
+    [1, 0, 0, 1, 1, 1, 1, 1],
+];
+
+pub struct Square {
+    pub sample: u16,
+    duty_cycle: [u8; 8],
+    duty_counter: u8,
+    length_counter_halt: bool, // (this bit is also the envelope's loop flag)
+    constant_volume_flag: bool, // (0: use volume from envelope; 1: use constant volume)
+    timer: usize,
+    pub length_counter: usize,
+    envelope: usize,
+    sweep: usize,
+    pub enabled: bool,
+}
+
+impl Square {
     pub fn new() -> Self {
-        super::Square {
-            duty_cycle: 0,
+        Square {
+            duty_cycle: duty_cycle_sequences[0],
+            duty_counter: 0,
             length_counter_halt: false,
             constant_volume_flag: false,
             timer: 0,
@@ -18,8 +39,10 @@ impl super::Square {
     }
 
     pub fn duty(&mut self, value: u8) {
-        self.duty_cycle = value >> 6;
-        // self.length_counter_halt = 
+        self.duty_cycle = duty_cycle_sequences[(value >> 6) as usize];
+        self.length_counter_halt = value & (1<<5) != 0;
+        self.constant_volume_flag = value & (1<<4) != 0;
+        
     }
 
     pub fn sweep(&mut self, value: u8) {
diff --git a/src/apu/triangle.rs b/src/apu/triangle.rs
index 5f156a7..a7f050b 100644
--- a/src/apu/triangle.rs
+++ b/src/apu/triangle.rs
@@ -1,6 +1,17 @@
-impl super::Triangle {
+
+// $4008 	Hlll.llll 	Triangle channel length counter halt and linear counter load (write)
+// bit 7 	H--- ---- 	Halt length counter (this bit is also the linear counter's control flag) 
+pub struct Triangle {
+    pub sample: u16,
+    timer: usize,
+    pub length_counter: usize, // (this bit is also the linear counter's control flag) 
+    linear_counter: usize,
+    pub enabled: bool,
+}
+
+impl Triangle {
     pub fn new() -> Self {
-        super::Triangle {
+        Triangle {
             timer: 0,
             length_counter: 0,
             linear_counter: 0,