Fix PPU timing

- DMA was being double-counted for PPU cycles

src/nes.c

@@ -43,9 +43,7 @@ void nes_mem_write(nes* sys, uint16_t addr, uint8_t val) {
                     nes_mem_read(sys, ((uint16_t)val << 8) + i);
         }
         sys->cpu.cycle += 513U;
-        sys->ppu.cycle += (513U * nes_clock_cpu_div) /
-                          nes_clock_ppu_div;
-        // TODO: Increment APU cycles?
+        // Other subsystem cycles are driven by CPU cycles
 
     } else if (addr < nes_mem_exp_start) {
         nes_apu_write(&sys->apu, addr, val);

src/nese.c

@@ -58,7 +58,7 @@ int main(int argc, char* argv[]) {
         int last_frame_rendered = -1;
         for (int i = 0; i < n_loops && status == 0; ++i) {
             int run = 0;
-            status = nes_run(&sys, 12, &run);
+            status = nes_run(&sys, nes_clock_cpu_div, &run);
             total_cycles += run;
 /*
             float us_run = (    run * 1000. * 1000. *

src/ppu.c

@@ -141,34 +141,27 @@ int nes_ppu_run(nes_ppu* ppu, int cycles) {
 
     ppu->cycle += cycles;
 
-    if (    0 != ppu->hit_line &&
-            ppu->scanline > ppu->hit_line &&
-            ppu->cycle > ppu->hit_dot) {
-        ppu->status |= ppu_Status_Hit;
-    }
-
     while (ppu->cycle >= nes_ppu_dots) {
         ppu->cycle -= nes_ppu_dots;
-        if (    ppu->scanline <= nes_ppu_prerender &&
+        if (    ppu->scanline < nes_ppu_prerender &&
                 (ppu->frame & 1)) {
             // Prerender line is one dot shorter in odd frames
             // Fake it by incrementing the cycle in this case
+            // TODO: Only if actually rendering
             ppu->cycle++;
         }
+
         ppu->scanline++;
-        if (ppu->scanline >= nes_ppu_prerender +
-                             nes_ppu_height +
-                             nes_ppu_postrender +
-                             nes_ppu_vblank) {
+
+        if (ppu->scanline >= nes_ppu_frame) {
             ppu->status &= ~(ppu_Status_VBlank | ppu_Status_Hit);
             ppu->hit_line = 0;
             ppu->hit_dot = 0;
-            ppu->scanline = 0;
+            ppu->scanline -= nes_ppu_frame;
             ppu->frame++;
-            // TODO: Render callback if vblank was previously set
-        } else if (ppu->scanline >= nes_ppu_prerender +
-                                    nes_ppu_height +
-                                    nes_ppu_postrender) {
+            // TODO: Render callback if vblank was previously set?
+
+        } else if (ppu->scanline >= nes_ppu_active) {
             ppu->status |= ppu_Status_VBlank;
             if (ppu->control & ppu_Control_VBlank) {
                 vblank = 1;
@@ -176,6 +169,12 @@ int nes_ppu_run(nes_ppu* ppu, int cycles) {
         }
     }
 
+    if (    0 != ppu->hit_line &&
+            ppu->scanline > ppu->hit_line &&
+            ppu->cycle > ppu->hit_dot) {
+        ppu->status |= ppu_Status_Hit;
+    }
+
     return vblank;
 }
 

src/ppu.h

@@ -10,15 +10,16 @@
 #define nes_ppu_postrender  (1U)
 #define nes_ppu_vblank      (20U)
 
-#define nes_ppu_active_cycles               \
-    (nes_ppu_dots * (nes_ppu_prerender +    \
-                     nes_ppu_height +       \
-                     nes_ppu_postrender))
+#define nes_ppu_active  (nes_ppu_prerender + \
+                         nes_ppu_height +    \
+                         nes_ppu_postrender)
 
-#define nes_ppu_vblank_cycles (nes_ppu_dots * nes_ppu_vblank)
+#define nes_ppu_frame   (nes_ppu_active + nes_ppu_vblank)
 
-#define nes_frame_cycles (nes_ppu_active_cycles + \
-                          nes_ppu_vblank_cycles)
+#define nes_ppu_active_cycles   (nes_ppu_dots * nes_ppu_active)
+#define nes_ppu_vblank_cycles   (nes_ppu_dots * nes_ppu_vblank)
+
+#define nes_ppu_frame_cycles    (nes_ppu_dots * nes_ppu_frame)
 
 #define nes_ppu_scan_w  (320U)  // Includes full overscan
 #define nes_ppu_scan_h  nes_ppu_height