fix the way ppu catches up with cpu

Author: Duckulus

src/cpu/bus.rs

@@ -8,31 +8,31 @@ pub struct Bus {
     rom: NesRom,
     prg_ram: Ram,
     pub ppu: Ppu<PpuMemory>,
-    cycle: u32
+    cycle: u32,
 }
 
 impl Bus {
-
     pub fn new(rom: NesRom) -> Self {
         Self {
             sram: Ram::new(0x8000),
             rom: rom.clone(),
             prg_ram: Ram::new(0x2000),
             ppu: Ppu::new(rom.chr_rom, rom.nametable_mirroring),
-            cycle: 0
+            cycle: 0,
         }
     }
 
     pub fn tick(&mut self, cycle: u32) {
+        let delta = cycle - self.cycle;
         self.cycle = cycle;
-        self.ppu.tick(cycle * 3);
+        self.ppu.tick(delta * 3);
     }
 
-    pub fn poll_nmi(&mut self) -> bool{
-       self.ppu.poll_nmi()
+    pub fn poll_nmi(&mut self) -> bool {
+        self.ppu.poll_nmi()
     }
 
-    pub fn poll_new_frame(&mut self) -> bool{
+    pub fn poll_new_frame(&mut self) -> bool {
         self.ppu.poll_new_frame()
     }
 
@@ -50,6 +50,9 @@ impl Bus {
                     a, register
                 ),
             }
+        } else if a == 0x4016 || a == 0x4017 {
+            // TODO
+            0
         } else if (0x6000..0x8000).contains(&a) {
             self.prg_ram.read(a - 0x6000)
         } else if a >= 0x8000 {
@@ -67,7 +70,9 @@ impl Bus {
             match register {
                 0 => self.ppu.write_ppu_ctrl(v),
                 1 => self.ppu.write_ppu_mask(v),
-                3 => unimplemented!(),
+                3 => {
+                    // unimplemented!()
+                }
                 4 => unimplemented!(),
                 5 => self.ppu.write_ppu_scroll(v),
                 6 => self.ppu.write_ppu_addr(v),
@@ -78,7 +83,9 @@ impl Bus {
                 ),
             };
         } else if a == 0x4014 {
-            unimplemented!()
+            // unimplemented!()
+        } else if (0x4000..=0x4017).contains(&a) {
+            // TODO APU
         } else if (0x6000..0x8000).contains(&a) {
             self.prg_ram.write(a - 0x6000, v);
         } else {
@@ -91,5 +98,4 @@ impl Bus {
         let lo = self.rom.prg_rom[(0xFFFC - 0x8000) % self.rom.prg_rom.len()] as u16;
         (hi << 8) | lo
     }
-
 }

src/ppu.rs

@@ -170,9 +170,9 @@ impl<M: Memory> Ppu<M> {
         }
     }
 
-    pub fn tick(&mut self, cycle: u32) {
-        self.cycle = cycle;
-        if self.cycle > SCANLINE_CYCLES {
+    pub fn tick(&mut self, delta: u32) {
+        self.cycle += delta;
+        while self.cycle > SCANLINE_CYCLES {
             self.cycle -= SCANLINE_CYCLES;
             self.scanline += 1;