chore: add Cycles to Ops, start to track cpu/ppu cycles

Author: nathanleiby

src/bus.rs

@@ -13,6 +13,7 @@ pub struct Bus {
     cpu_vram: [u8; 0x800], // 2048
     rom: Rom,
     ppu: Ppu,
+    cycles: usize,
 }
 
 impl Bus {
@@ -23,9 +24,19 @@ impl Bus {
             cpu_vram: [0; 0x800],
             rom,
             ppu,
+            cycles: 0,
         }
     }
 
+    pub fn tick(&mut self, cycles: usize) {
+        self.cycles += cycles;
+        self.ppu.tick(cycles * 3);
+    }
+
+    pub fn poll_nmi_status(&mut self) -> bool {
+        self.ppu.is_nmi_interrupt_triggered()
+    }
+
     fn read_prg_rom(&self, addr: u16) -> u8 {
         let mut idx = addr - PRG_ROM_START;
 

src/core.rs

@@ -245,12 +245,24 @@ impl Cpu {
         F: FnMut(&mut Cpu),
     {
         loop {
+            if self.bus.poll_nmi_status() {
+                todo!("implement NMI interrupt");
+                // self.interrupt_nmi();
+            }
+
             callback(self);
 
             let opcode = self.mem_read(self.pc);
             self.pc += 1;
 
-            let (name, mode) = lookup_opcode(opcode);
+            let (name, cycles, mode) = lookup_opcode(opcode);
+            if cycles.0 == 0 {
+                todo!(
+                    "cycles is mistakenly set to 0 for {} (0x{:02X}) ",
+                    name,
+                    opcode
+                );
+            }
             let size = addressing_mode_to_size(&mode);
 
             let saved_pc = self.pc;
@@ -336,6 +348,13 @@ impl Cpu {
                 OpName::RRA => self.rra(&mode),
             }
 
+            // TODO: Handle extra cycles behavior
+            // (1) page wrapping behavior for some ops that adds +1 to the number of cycles
+            //      Memory page size is 256 bytes. For example, the range [0x0000 .. 0x00FF]- belongs to page 0, [0x0100 .. 0x01FF] belongs to page 1, etc.
+            //     It's enough to compare the upper byte of the addresses to see if they are on the same page.
+            // (2) branching behavior that adds +1 or +2 to cycles
+            self.bus.tick(cycles.0 as usize);
+
             // some operations modify the pc, like JMP. We shouldn't override that.
             if self.pc == saved_pc {
                 self.pc += size - 1;
@@ -836,7 +855,7 @@ impl Cpu {
         //// Address syntax by mode looks like:
 
         let op = lookup_opcode(code);
-        let (name, mode) = op;
+        let (name, _, mode) = op;
         let size = addressing_mode_to_size(&mode);
 
         let tla = format!("{}{}", if is_official(code) { "" } else { "*" }, name);