diff --git a/src/apu.rs b/src/apu.rs
index aec71d3..075a05f 100644
--- a/src/apu.rs
+++ b/src/apu.rs
@@ -4,7 +4,7 @@ bitfield::bitfield! {
     pub struct DutyVol(u8);
     impl Debug;
     duty, set_duty: 7, 6;
-    r#loop, set_loop: 5;
+    length_counter_halt, set_length_counter_halt: 5;
     const_vol, set_const_vol: 4;
     volume, set_volume: 3, 0;
 }
@@ -27,6 +27,62 @@ bitfield::bitfield! {
 
 struct PulseChannel {
     enabled: bool,
+    duty_vol: DutyVol,
+    sweep: Sweep,
+    timer_low: u8,
+    length_timer_high: LengthTimerHigh,
+
+    cur_time: u16,
+    cur_length: u8,
+}
+
+impl PulseChannel {
+    pub fn new() -> Self {
+        Self {
+            enabled: false,
+            duty_vol: DutyVol(0),
+            sweep: Sweep(0),
+            timer_low: 0,
+            length_timer_high: LengthTimerHigh(0),
+            cur_time: 0,
+            cur_length: 0,
+        }
+    }
+    fn use_envelope(&self) -> bool {
+        !self.duty_vol.const_vol()
+    }
+    fn volume(&self) -> u8 {
+        self.duty_vol.volume()
+    }
+    fn timer(&self) -> u16 {
+        self.timer_low as u16 | ((self.length_timer_high.timer_high() as u16) << 8)
+    }
+    fn length(&self) -> u8 {
+        self.length_timer_high.length()
+    }
+
+    pub fn reset(&mut self) {
+        // TODO
+        self.cur_time = self.timer();
+    }
+    pub fn clock(&mut self) {
+        if self.cur_time == 0 {
+            self.cur_time = self.timer();
+        } else {
+            self.cur_time -= 1;
+        }
+        // TODO
+    }
+    pub fn q_frame_clock(&mut self) {
+        if !self.duty_vol.length_counter_halt() && self.cur_length > 0 {
+            self.cur_length -= 1;
+        }
+    }
+    pub fn h_frame_clock(&mut self) {
+        if !self.duty_vol.length_counter_halt() && self.cur_length > 0 {
+            self.cur_length -= 1;
+        }
+    }
 }
 
 bitfield::bitfield! {
@@ -46,6 +102,12 @@ struct DeltaChannel {
     enabled: bool,
 }
 
+impl DeltaChannel {
+    pub fn int(&self) -> bool {
+        false
+    }
+}
+
 struct FrameCounter {
     count: usize,
     mode_5_step: bool,
@@ -76,8 +138,8 @@ impl std::fmt::Debug for APU {
 impl APU {
     pub fn init() -> Self {
         Self {
-            pulse_1: PulseChannel { enabled: false },
-            pulse_2: PulseChannel { enabled: false },
+            pulse_1: PulseChannel::new(),
+            pulse_2: PulseChannel::new(),
             triangle: TriangleChannel { enabled: false },
             noise: NoiseChannel { enabled: false },
             dmc: DeltaChannel { enabled: false },
@@ -90,18 +152,38 @@ impl APU {
         }
     }
     pub fn read_reg(&mut self, offset: u16) -> u8 {
+        // println!("APU read: {offset:02X}");
         match offset {
+            0x15 => {
+                let val = (u8::from(self.dmc.int()) << 7)
+                    | (u8::from(self.frame_counter.irq) << 6)
+                    | (u8::from(self.dmc.enabled) << 4)
+                    | (u8::from(self.noise.enabled) << 3)
+                    | (u8::from(self.triangle.enabled) << 2)
+                    | (u8::from(self.pulse_2.enabled) << 1)
+                    | (u8::from(self.pulse_1.enabled) << 0);
+                self.frame_counter.irq = false;
+                val
+            }
             _ => panic!("No register at {:X}", offset),
         }
     }
     pub fn write_reg(&mut self, offset: u16, val: u8) {
+        // println!("APU write: {offset:02X} <= {val:02X}");
         match offset {
-            0x15 => {
-                self.dmc.enabled = val & 0b0001_0000 != 0;
-                self.noise.enabled = val & 0b0000_1000 != 0;
-                self.triangle.enabled = val & 0b0000_0100 != 0;
-                self.pulse_2.enabled = val & 0b0000_0010 != 0;
-                self.pulse_1.enabled = val & 0b0000_0001 != 0;
+            0x00 => self.pulse_1.duty_vol.0 = val,
+            0x01 => self.pulse_1.sweep.0 = val,
+            0x02 => self.pulse_1.timer_low = val,
+            0x03 => {
+                self.pulse_1.length_timer_high.0 = val;
+                self.pulse_1.reset();
+            }
+            0x04 => self.pulse_2.duty_vol.0 = val,
+            0x05 => self.pulse_2.sweep.0 = val,
+            0x06 => self.pulse_2.timer_low = val,
+            0x07 => {
+                self.pulse_2.length_timer_high.0 = val;
+                self.pulse_2.reset();
             }
             0x10 => {
                 assert_eq!(val, 0x00);
@@ -110,27 +192,60 @@ impl APU {
             0x11 => {
                 // TODO: load dmc counter with (val & 7F)
             }
-            _ => (),
-            // _ => panic!("No register at {:X}", offset),
+            0x15 => {
+                self.dmc.enabled = val & 0b0001_0000 != 0;
+                self.noise.enabled = val & 0b0000_1000 != 0;
+                self.triangle.enabled = val & 0b0000_0100 != 0;
+                self.pulse_2.enabled = val & 0b0000_0010 != 0;
+                self.pulse_1.enabled = val & 0b0000_0001 != 0;
+            }
+            0x17 => {
+                self.frame_counter.mode_5_step = val & 0b1000_0000 == 0;
+                self.frame_counter.interrupt_enabled = val & 0b0100_0000 == 0;
+                if !self.frame_counter.interrupt_enabled {
+                    self.frame_counter.irq = false;
+                }
+            }
+            // _ => (),
+            _ => panic!("No register at {:X}", offset),
         }
     }
 
+    fn q_frame_clock(&mut self) {
+        self.pulse_1.q_frame_clock();
+        self.pulse_2.q_frame_clock(); // TODO: clock all
+    }
+    fn h_frame_clock(&mut self) {
+        self.pulse_1.q_frame_clock();
+        self.pulse_1.h_frame_clock();
+        self.pulse_2.q_frame_clock();
+        self.pulse_2.h_frame_clock();
+    }
+
     pub fn run_one_clock_cycle(&mut self, ppu_cycle: usize) -> bool {
         if ppu_cycle % 6 == 1 {
             // APU Frame Counter clock cycle
-            if !self.frame_counter.mode_5_step
-                && self.frame_counter.interrupt_enabled
-                && self.frame_counter.count == 14914
-            {
-                self.frame_counter.irq = true;
-            } else if !self.frame_counter.mode_5_step
-                && self.frame_counter.interrupt_enabled
-                && self.frame_counter.count == 14915
-            {
-                self.frame_counter.irq = true;
-                self.frame_counter.count = 0;
+            if self.frame_counter.mode_5_step {
+                todo!()
+            } else {
+                if self.frame_counter.count == 3728 {
+                    self.q_frame_clock();
+                } else if self.frame_counter.count == 7456 {
+                    self.h_frame_clock();
+                } else if self.frame_counter.count == 11185 {
+                    self.q_frame_clock();
+                } else if self.frame_counter.count == 14914 {
+                    self.frame_counter.irq = self.frame_counter.interrupt_enabled;
+                    self.h_frame_clock();
+                } else if self.frame_counter.count == 14915 {
+                    self.frame_counter.count = 0;
+                    self.frame_counter.irq = self.frame_counter.interrupt_enabled;
+                }
             }
             self.frame_counter.count += 1;
+
+            self.pulse_1.clock();
+            self.pulse_2.clock();
         }
         false
     }
@@ -144,8 +259,6 @@ impl APU {
         self.frame_counter.irq
     }
     pub fn irq_waiting(&mut self) -> bool {
-        let res = self.frame_counter.irq;
-        self.frame_counter.irq = false;
-        res
+        self.frame_counter.irq
     }
 }
diff --git a/src/ppu.rs b/src/ppu.rs
index 19240ae..ba48ebb 100644
--- a/src/ppu.rs
+++ b/src/ppu.rs
@@ -467,7 +467,7 @@ impl Palette {
 
 pub struct PPU {
     // registers: PPURegisters,
-    frame_count: usize,
+    pub frame_count: usize,
     nmi_enabled: bool,
     // nmi_waiting: bool,
     pub even: bool,