diff --git a/src/apu.c b/src/apu.c
index 7ef935a..6ac9a7f 100644
--- a/src/apu.c
+++ b/src/apu.c
@@ -1,25 +1,35 @@
 #include "memory.h"
 
+//#define NESE_DEBUG "APU"
+#include "log.h"
+
 
 void nes_apu_init(nes_APU* apu, nes_APU_Memory* mem, int freq) {
-    // TODO
+    apu->frame_delay = nes_apu_quarter_frame_ticks;
+    // TODO: Set LFSR?
 }
 
-int nes_apu_hsync(nes_APU* apu, nes_Memory* core_mem) {
+static int nes_apu_run(nes_APU* apu, nes_Memory* core_mem,
+                       int ticks) {
+//    int ret = 0;
     nes_APU_Memory* mem = &core_mem->apu;
 
     for (int i = 0; i < core_mem->apu.n_events; ++i) {
         int reg = core_mem->apu.events[i].reg;
         int val = core_mem->apu.events[i].val;
 
+        LOGD("$40%02X < %02X", reg, val);
+
         switch (reg) {
         // TODO: 0x00 - 0x13
         // TODO: 0x15
         case 0x17: // Frame Counter
-            apu->frame_reg = val & (    apu_Frame_Mode |
-                                        apu_Frame_Inhibit);
+            (void)val;
+#if 0
+            val &= (apu_Frame_Mode | apu_Frame_Inhibit);
+            apu->frame_reg = val;
             apu->frame = 0;
-            apu->frame_delay = 0;
+            apu->frame_delay = nes_apu_quarter_frame_ticks;
 
             if (val & apu_Frame_Mode) {
                 // TODO
@@ -32,9 +42,8 @@ int nes_apu_hsync(nes_APU* apu, nes_Memory* core_mem) {
             if (val & apu_Frame_Inhibit) {
                 mem->status &= ~apu_Status_Frame_Int;
             }
-
+#endif
             break;
-
         }
     }
 
@@ -42,10 +51,11 @@ int nes_apu_hsync(nes_APU* apu, nes_Memory* core_mem) {
 
     // Frame advance
 
-    apu->frame_delay += nes_apu_hsync_ticks;
+    apu->frame_delay -= ticks;
 
-    if (apu->frame_delay >= nes_apu_quarter_frame_ticks) {
-        apu->frame_delay -= nes_apu_quarter_frame_ticks;
+    if (apu->frame_delay <= 0) {
+        LOGD("Quarter Frame (%d overshoot)", -apu->frame_delay);
+        apu->frame_delay += nes_apu_quarter_frame_ticks;
 
         int end = 0;
         int quarter_frame = 1;
@@ -80,8 +90,10 @@ int nes_apu_hsync(nes_APU* apu, nes_Memory* core_mem) {
         }
 
         if (end) {
+            LOGD("Frame sequence end (frame_reg %02X)", apu->frame_reg);
             if (0 == apu->frame_reg) {
                 mem->status |= apu_Status_Frame_Int;
+//                ret = 1;
             }
             apu->frame = 0;
         } else {
@@ -92,4 +104,17 @@ int nes_apu_hsync(nes_APU* apu, nes_Memory* core_mem) {
     // TODO: DMC Interrupt
 
     return (mem->status & apu_Status_Frame_Int);
+//    return ret;
+}
+
+int nes_apu_hsync(nes_APU* apu, nes_Memory* core_mem) {
+    int ticks = nes_apu_hsync_ticks - apu->ticks_handled;
+    apu->ticks_handled = 0;
+    return nes_apu_run(apu, core_mem, ticks);
+}
+
+int nes_apu_finish_qframe(nes_APU* apu, nes_Memory* core_mem) {
+    LOGD("Finishing Quarter Frame (%d remain)", apu->frame_delay);
+    apu->ticks_handled = apu->frame_delay;
+    return nes_apu_run(apu, core_mem, apu->frame_delay);
 }
diff --git a/src/apu.h b/src/apu.h
index 82d886e..2994a2d 100644
--- a/src/apu.h
+++ b/src/apu.h
@@ -4,8 +4,9 @@
 #include <stdint.h>
 
 
-#define nes_apu_hsync_ticks         (4U)
-#define nes_apu_quarter_frame_ticks (262U)
+#define nes_ppu_to_apu_tick_ratio   (4U)
+#define nes_apu_hsync_ticks         (341U * 4U)
+#define nes_apu_quarter_frame_ticks (341U * 262U)
 
 
 typedef struct {
@@ -90,6 +91,7 @@ typedef struct {
     nes_apu_Frame frame_reg;
     int frame;
     int frame_delay;
+    int ticks_handled;
 
     uint8_t reg[20];
 
@@ -100,6 +102,7 @@ struct nes_Memory;
 
 void nes_apu_init(nes_APU* apu, nes_APU_Memory* mem, int freq);
 int nes_apu_hsync(nes_APU*, struct nes_Memory*);
+int nes_apu_finish_qframe(nes_APU*, struct nes_Memory*);
 
 
 #endif // NESE_APU_H_
diff --git a/src/f6502.c b/src/f6502.c
index 90800a4..2f0dfcc 100644
--- a/src/f6502.c
+++ b/src/f6502.c
@@ -9,12 +9,12 @@
 #include <stdio.h>
 #endif
 
-#ifdef F6502_TEST
+#include "nes.h"
+
 #include <stddef.h>
 #define container_of(ptr, type, member) ({                      \
         const typeof( ((type *)0)->member ) *__mptr = (ptr);    \
         (type *)((char *)__mptr - offsetof(type,member));})
-#endif
 
 //#define NESE_DEBUG "Core"
 #include "log.h"
@@ -98,8 +98,12 @@ static inline uint8_t f6502_read(nes_Memory* mem,
     case 0x4000:
         switch (addr & 0x1FU) {
         case 0x15:  /* APU Status */
-        {   uint8_t ret = mem->apu.status;
+        {   f6502_Core* core = container_of(mem, f6502_Core, memory);
+
+            uint8_t ret = mem->apu.status;
             mem->apu.status &= ~apu_Status_Frame_Int;
+            f6502_set_IRQ(core, 0);
+
             return ret;
         }
 
@@ -264,12 +268,22 @@ static inline int f6502_write(nes_Memory* mem,
     case 0x4000:
         switch (addr & 0x1FU) {
         case 0x17:  // APU Frame
-            // TODO: Clear interrupt here?
-            /*
-            if (val & apu_Frame_apu_Frame_Inhibit) {
-                f6502_Int_IRQ(core, 0);
+        {   f6502_Core* core = container_of(mem, f6502_Core, memory);
+            nes* sys = container_of(core, nes, core);
+            nes_APU* apu = &sys->apu;
+
+//            printf("APU: $%04X < %02X\n", addr, val);
+
+            apu->frame_reg = val;
+            apu->frame = 0;
+            apu->frame_delay = nes_apu_quarter_frame_ticks;
+
+            // Clear this ASAP
+            if (val & apu_Frame_Inhibit) {
+                mem->apu.status &= ~apu_Status_Frame_Int;
+                f6502_set_IRQ(core, 0);
             }
-            */
+        }
         case 0x00:
         case 0x01:
         case 0x02:
@@ -437,8 +451,10 @@ static inline bool f6502_irq_ready(const f6502_Core* core) {
 static inline int f6502_check_interrupts(f6502_Core* core) {
     if (f6502_nmi_ready(core)) {
         core->interrupts |= f6502_Int_NMI_Serviced;
+        LOGI("%lu: NMI", core->clocks);
         return f6502_interrupt(core, f6502_Vector_NMI);
     } else if (f6502_irq_ready(core)) {
+        LOGI("%lu: IRQ", core->clocks);
         return f6502_interrupt(core, f6502_Vector_IRQ);
     }
     return 0;
@@ -1704,6 +1720,8 @@ int f6502_step(f6502_Core* core, int clocks) {
     }
 */
     clocks_elapsed += f6502_check_interrupts(core);
-    return (    f6502_do_step(core, clocks - clocks_elapsed) +
-                clocks_elapsed);
+    clocks_elapsed += f6502_do_step(core,
+                                    clocks - clocks_elapsed);
+    core->clocks += clocks_elapsed;
+    return clocks_elapsed;
 }
diff --git a/src/f6502.h b/src/f6502.h
index d5791f8..803e1c7 100644
--- a/src/f6502.h
+++ b/src/f6502.h
@@ -41,6 +41,7 @@ typedef enum {
 } f6502_Interrupt;
 
 struct f6502_Core {
+    uint64_t clocks;
     f6502_Registers registers;
     f6502_Interrupt interrupts;
     nes_Memory memory;
diff --git a/src/nes.c b/src/nes.c
index 3a018c0..ee5cae9 100644
--- a/src/nes.c
+++ b/src/nes.c
@@ -3,7 +3,7 @@
 #include "nes.h"
 #include "port.h"
 
-//#define NESE_DEBUG "NES"
+#define NESE_DEBUG "NES"
 #include "log.h"
 
 
@@ -88,7 +88,6 @@ static int nes_hsync(nes* sys, void* plat) {
         // Emulate the happy part of the backdrop override quirk
         int pal_idx = ((mem->addr & 0x3F00U) == 0x3F00U) ?
                       (mem->addr & 0x1FU) : 0;
-        LOGD("Background: %d", pal_idx);
         // Don't use the rendering palette (masked transparency)
         status = nese_frame_start(plat, mem->pal_bank[0x300 + pal_idx] & 0x3FU);
 
@@ -117,7 +116,6 @@ int nes_loop(nes* sys, void* plat) {
     bool vbl_clear = false;
 
     while (0 == status) {
-        // TODO: Move to inline PPU function?
         int target_dot = nes_ppu_scanline_dots;
 
         if (    nes_ppu_frame_end_line - 1 == sys->ppu.scanline &&
@@ -148,6 +146,26 @@ int nes_loop(nes* sys, void* plat) {
         }
 
         int dots_to_run = target_dot - dot;
+
+        // Will APU quarter frame hit this line?
+        // TODO: Only do this when the IRQ is pending?
+        if (sys->apu.frame_delay <= nes_apu_hsync_ticks) {
+            int qframe_dot = (
+                    (   sys->apu.frame_delay +
+                        (nes_ppu_to_apu_tick_ratio - 1)) /
+                    nes_ppu_to_apu_tick_ratio
+                );
+            if (dot >= qframe_dot) {
+                int irq = nes_apu_finish_qframe(
+                        &sys->apu, &sys->core.memory
+                    );
+                // TODO: How might this interfere with MMC3?
+                f6502_set_IRQ(&sys->core, irq);
+            } else {
+                dots_to_run = qframe_dot - dot;
+            }
+        }
+
         if (dots_to_run > 0) {
             int cpu_cycles = (dots_to_run + 2) / 3;
             dot += 3 * f6502_step(&sys->core, cpu_cycles);