diff --git a/src/apu/mod.rs b/src/apu/mod.rs
index eb5d53f..3acfb11 100644
--- a/src/apu/mod.rs
+++ b/src/apu/mod.rs
@@ -16,7 +16,7 @@ pub struct Apu {
 
 struct Square {
     sample: u16,
-    duty_cycle: usize,
+    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,
@@ -49,6 +49,12 @@ struct DMC {
     sample: u16,
 }
 
+struct Envelope {
+    start_flag: bool,
+    divider: usize,
+    delay_level_counter: usize,
+}
+
 impl Apu {
     fn new() -> Self {
         let square_table = (0..31).map(|x| 95.52/(8128.0 / x as f32) + 100.0).collect();
diff --git a/src/apu/square.rs b/src/apu/square.rs
index 77b0572..79609d0 100644
--- a/src/apu/square.rs
+++ b/src/apu/square.rs
@@ -17,7 +17,8 @@ impl super::Square {
     }
 
     pub fn duty(&mut self, value: u8) {
-
+        self.duty_cycle = value >> 6;
+        self.length_counter_halt = 
     }
 
     pub fn sweep(&mut self, value: u8) {