From 96ec7c584cfa49e7647a1fd9c06e1b2a8e451fb9 Mon Sep 17 00:00:00 2001
From: Nathaniel Walizer <robots.are.love@gmail.com>
Date: Thu, 20 Mar 2025 20:06:45 -0700
Subject: [PATCH] Wire up APU interrupt

---
 src/apu.c   |  6 +++++-
 src/apu.h   |  2 +-
 src/f6502.c | 17 +++++++++++++----
 src/nes.c   |  7 +++----
 4 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/src/apu.c b/src/apu.c
index 9e47746..7ef935a 100644
--- a/src/apu.c
+++ b/src/apu.c
@@ -5,7 +5,7 @@ void nes_apu_init(nes_APU* apu, nes_APU_Memory* mem, int freq) {
     // TODO
 }
 
-void nes_apu_hsync(nes_APU* apu, nes_Memory* core_mem) {
+int nes_apu_hsync(nes_APU* apu, nes_Memory* core_mem) {
     nes_APU_Memory* mem = &core_mem->apu;
 
     for (int i = 0; i < core_mem->apu.n_events; ++i) {
@@ -88,4 +88,8 @@ void nes_apu_hsync(nes_APU* apu, nes_Memory* core_mem) {
             apu->frame++;
         }
     }
+
+    // TODO: DMC Interrupt
+
+    return (mem->status & apu_Status_Frame_Int);
 }
diff --git a/src/apu.h b/src/apu.h
index 65fdd96..82d886e 100644
--- a/src/apu.h
+++ b/src/apu.h
@@ -99,7 +99,7 @@ typedef struct {
 struct nes_Memory;
 
 void nes_apu_init(nes_APU* apu, nes_APU_Memory* mem, int freq);
-void nes_apu_hsync(nes_APU*, struct nes_Memory*);
+int nes_apu_hsync(nes_APU*, struct nes_Memory*);
 
 
 #endif // NESE_APU_H_
diff --git a/src/f6502.c b/src/f6502.c
index 1c9538d..f5defa1 100644
--- a/src/f6502.c
+++ b/src/f6502.c
@@ -90,8 +90,11 @@ static inline uint8_t f6502_read(nes_Memory* mem,
 
     case 0x4000:
         switch (addr & 0x1FU) {
-        case 0x15:
-            return mem->apu.status;
+        case 0x15:  /* APU Status */
+        {   uint8_t ret = mem->apu.status;
+            mem->apu.status &= ~apu_Status_Frame_Int;
+            return ret;
+        }
 
         case 0x16:
         case 0x17:
@@ -253,6 +256,13 @@ 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);
+            }
+            */
         case 0x00:
         case 0x01:
         case 0x02:
@@ -273,8 +283,7 @@ static inline int f6502_write(nes_Memory* mem,
         case 0x11:
         case 0x12:
         case 0x13:
-        case 0x15:
-        case 0x17:
+        case 0x15:  // APU Status
             if (mem->apu.n_events >= APU_MAX_EVENTS) {
                 LOGE("APU event buffer full");
             } else {
diff --git a/src/nes.c b/src/nes.c
index 153b35e..36ac1df 100644
--- a/src/nes.c
+++ b/src/nes.c
@@ -33,9 +33,6 @@ static int nes_vsync(nes* sys, void* plat) {
         f6502_set_NMI(&sys->core, 1);
     }
 
-    // TODO: APU Sync
-    // TODO: APU Frame IRQ
-
     nes_Memory* mem = &sys->core.memory;
     if (0 == status && NULL != mem->mapper.vsync) {
         mem->mapper.vsync(&mem->mapper);
@@ -48,7 +45,9 @@ static int nes_vsync(nes* sys, void* plat) {
 static int nes_hsync(nes* sys, void* plat) {
     int status = 0;
 
-    nes_apu_hsync(&sys->apu, &sys->core.memory);
+    int irq = nes_apu_hsync(&sys->apu, &sys->core.memory);
+    // TODO: How might this interfere with MMC3?
+    f6502_set_IRQ(&sys->core, irq);
 
     if (sys->ppu.scanline < nes_ppu_postrender_line) {
         if (sys->ppu.scanline < nes_ppu_visible_line) {