brokem implementation on main.rs - no regression

src/bus.rs

@@ -1,4 +1,4 @@
-use crate::cartridge::Cartridge;
+use crate::{cartridge::Cartridge, ppu::Ppu};
 
 pub trait Bus {
     fn read(&mut self, address: u16) -> u8;
@@ -8,32 +8,38 @@ pub trait Bus {
 pub struct NesBus {
     ram: [u8; 0x800], // 2KB fixed array, mirrors to fill $0000 to $1FFF
     cart: Cartridge,
+    ppu: Ppu,
+    openbus: u8, // last byte on the CPU data bus
 }
 
 impl NesBus {
     pub fn new(cart: Cartridge) -> Self {
-        Self { ram: [0; 0x800], cart }
+        Self { ram: [0; 0x800], cart, ppu: Ppu::new(), openbus: 0 }
     }
 }
 
 impl Bus for NesBus {
     fn read(&mut self, address: u16) -> u8 {
-        match address {
+        let result = match address {
             0x0000..=0x1FFF => self.ram[(address & 0x07FF) as usize], // Zero-Page my beloved
-            0x2000..=0x3FFF => 0, //PPU registers stub, temporal
-            0x4000..=0x401F => 0, //APU controller stub, temporal
-            0x4020..=0x5FFF => 0, //Expansion ROM stub. temporal
+            0x2000..=0x3FFF => self.ppu.read(&mut self.cart, address, self.openbus),
+            0x4000..=0x401F => self.openbus,  // APU regs: unmapped reads return bus contents
+            0x4020..=0x5FFF => self.openbus,  // expansion: open bus
             0x6000..=0x7FFF => self.cart.read_prg_ram(address), // SRAM reads from the cartridge
             0x8000..=0xFFFF => self.cart.read_prg(address), // this is te space PRG Rom gets "loaded" to in real hardware
-        }
+        };
+        self.openbus = result;
+        result
     }
 
     fn write(&mut self, address: u16, value: u8) {
         match address {
             0x0000..=0x1FFF => self.ram[(address & 0x07FF) as usize] = value,
+            0x2000..=0x3FFF => self.ppu.write(&mut self.cart, address, value),
             0x6000..=0x7FFF => self.cart.write_prg_ram(address, value),
             0x8000..=0xFFFF => self.cart.write_prg(address, value),
             _ => {} // Everything else dropped for now
         }
+        self.openbus = value;
     }
 }