added basic cartridge functions

src/bus.rs

@@ -2,10 +2,12 @@ use std::cell::RefCell;
 use std::rc::{Rc, Weak};
 
 use crate::cpu::CPU;
+use crate::cartridge::Cartridge;
 
 pub struct Bus
 {
 	cpu: Weak<RefCell<CPU>>,
+	cartridge: Cartridge,
 
 	ram: Vec<u8>
 }
@@ -17,6 +19,7 @@ impl Bus
 		Bus 
 		{
 			cpu: Weak::new(),
+			cartridge: Cartridge::new("roms/nestest.nes"),
 			ram: vec![0; 0x800]
 		}
 	}
@@ -38,6 +41,12 @@ impl Bus
 
 	pub fn read_cpu(&self, addr: u16) -> u8 
 	{
-		self.ram[addr as usize]
+		match addr
+		{
+			0..=0x1FFF 		=> self.ram[(addr & 0x7FF) as usize],
+			0x8000..=0xFFFF => self.cartridge.read_prg(addr & 0x7FFF),
+
+			_ => panic!("Tried to access invalid memory address {}", addr)
+		}
 	}
 }

src/cartridge.rs

@@ -0,0 +1,54 @@
+use std::fs;
+
+struct Header 
+{
+	prg_blocks: u8,
+	chr_blocks: u8
+}
+
+pub struct Cartridge
+{
+	header: Header,
+
+	prg: Vec<u8>,
+	chr: Vec<u8>
+}
+
+impl Cartridge 
+{
+	pub fn new(filepath: &str) -> Cartridge 
+	{
+		let contents = fs::read(filepath).expect("Failed to load ROM");
+		let iter = contents.iter();
+
+		let mut curr_pos: usize = 0;
+
+		let header_data = &contents[curr_pos..curr_pos + 16];
+		let header = Header {
+			prg_blocks: header_data[4],
+			chr_blocks: header_data[5]
+		};
+
+		// TODO: For now assume there is no trainer
+		curr_pos = 16;
+		let prg_data = &contents[curr_pos..(curr_pos + 0x4000 * header.prg_blocks as usize)];
+
+		curr_pos += 0x4000 * header.prg_blocks as usize;
+		let chr_data = &contents[curr_pos..(curr_pos + 0x2000 * header.chr_blocks as usize)];
+
+		Cartridge 
+		{ 
+			header: header,
+
+			prg: prg_data.to_vec(), 
+			chr: chr_data.to_vec()
+		}
+	}
+
+	// TODO: For now all memio is hardcoded to work with nestest.nes for testing
+
+	pub fn read_prg(&self, addr: u16) -> u8 
+	{
+		self.prg[(addr & 0x3FFF) as usize]
+	}
+}

src/cpu.rs

@@ -41,6 +41,9 @@ impl CPU
 		self.x = 0;
 		self.y = 0;
 		self.sp = 0xFD;
+
+		// TODO: This is just for the nestest.nes
+		self.pc = 0xC000;
 	}
 
 	pub fn execute(&mut self)
@@ -51,7 +54,7 @@ impl CPU
 
 		match (opcode)
 		{
-			_ => panic!("Unimplemented opcode {}", opcode)
+			_ => panic!("Unimplemented opcode {:X}", opcode)
 		}
 	}
 }

src/main.rs

@@ -1,6 +1,7 @@
 mod nes;
 mod bus;
 mod cpu;
+mod cartridge;
 
 use nes::NES;