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use rand::Rng;
use std::fs;
use std::io::Read;
const w: usize = 64;
const h: usize = 32;
pub struct Chip8 {
opcode: u16,
memory: [u8; 4096],
v: [u8; 16],
index: u16,
pc: u16,
pub gfx: [u8; w * h],
delay_timer: u8,
sound_timer: u8,
stack: [u16; 16],
sp: isize,
key: [u8; 16],
pub draw_flag: bool,
}
const font_set: [u8; 80] = [
0xF0, 0x90, 0x90, 0x90, 0xF0, // 0
0x20, 0x60, 0x20, 0x20, 0x70, // 1
0xF0, 0x10, 0xF0, 0x80, 0xF0, // 2
0xF0, 0x10, 0xF0, 0x10, 0xF0, // 3
0x90, 0x90, 0xF0, 0x10, 0x10, // 4
0xF0, 0x80, 0xF0, 0x10, 0xF0, // 5
0xF0, 0x80, 0xF0, 0x90, 0xF0, // 6
0xF0, 0x10, 0x20, 0x40, 0x40, // 7
0xF0, 0x90, 0xF0, 0x90, 0xF0, // 8
0xF0, 0x90, 0xF0, 0x10, 0xF0, // 9
0xF0, 0x90, 0xF0, 0x90, 0x90, // A
0xE0, 0x90, 0xE0, 0x90, 0xE0, // B
0xF0, 0x80, 0x80, 0x80, 0xF0, // C
0xE0, 0x90, 0x90, 0x90, 0xE0, // D
0xF0, 0x80, 0xF0, 0x80, 0xF0, // E
0xF0, 0x80, 0xF0, 0x80, 0x80, // F
];
impl Chip8 {
pub fn new() -> Chip8 {
let mut c = Chip8 {
opcode: 0,
memory: [0; 4096],
v: [0; 16],
index: 0,
pc: 0x200,
gfx: [0; w * h],
delay_timer: 0,
sound_timer: 0,
stack: [0; 16],
sp: 0,
key: [0; 16],
draw_flag: false,
};
for i in 0..font_set.len() {
c.memory[i] = font_set[i];
}
c
}
pub fn load_game(&mut self, filepath: &str) {
let mut f = fs::File::open(filepath).expect("can not load rom file");
let metadata = fs::metadata(filepath).expect("unable to read metadata");
let mut b = vec![0; metadata.len() as usize];
f.read(&mut b).expect("buffer overflow");
for i in 0..b.len() {
self.memory[512 + i] = b[i];
}
}
pub fn emulate_cycle(&mut self) {
self.opcode = (self.memory[self.pc as usize] as u16) << 8
| self.memory[(self.pc + 1) as usize] as u16;
let x: usize = ((self.opcode & 0x0F00) >> 8) as usize;
let y: usize = ((self.opcode & 0x00F0) >> 4) as usize;
let nn: u8 = (self.opcode & 0x00FF) as u8;
let nnn: u16 = (self.opcode & 0x0FFF) as u16;
// Decode Opcode
// https://en.wikipedia.org/wiki/CHIP-8#Opcode_table
match self.opcode & 0xF000 {
0x0000 => {
match self.opcode & 0x000F {
0x0000 => {
// 00E0 Clear screen
for i in 0..self.gfx.len() {
self.gfx[i] = 0;
}
self.pc += 2;
self.draw_flag = true;
}
0x000E => {
// 00EE Returns from a subroutine
self.sp -= 1;
self.pc = self.stack[self.sp as usize];
self.pc += 2;
}
_ => println!("unk {:x}", self.opcode),
}
}
0x1000 => {
// 1NNN Jumps to address NNN
self.pc = nnn;
}
0x2000 => {
// 2NNN Calls subroutine at NNN
self.stack[self.sp as usize] = self.pc;
self.sp += 1;
self.pc = nnn;
}
0x3000 => {
// 3XNN Skips the next instruction if VX equals NN. (Usually
// the next instruction is a jump to skip a code block)
if self.v[x] == nn {
self.pc += 2;
}
self.pc += 2;
}
0x4000 => {
// 4XNN Skips the next instruction if VX doesn't equal NN.
// (Usually the next instruction is a jump to skip a code
// block)
if self.v[x] != nn {
self.pc += 2;
}
self.pc += 2;
}
0x5000 => {
// 5XY0 Skips the next instruction if VX equals VY. (Usually
// the next instruction is a jump to skip a code block)
if self.v[x] == self.v[y] {
self.pc += 2;
}
self.pc += 2;
}
0x6000 => {
// 6XNN Sets VX to NN
self.v[x] = nn;
self.pc += 2;
}
0x7000 => {
// 7XNN Adds NN to VX. (Carry flag is not changed)
self.v[x] += nn;
self.pc += 2;
}
0x8000 => {
match self.opcode & 0x000F {
0x0000 => {
// 0x8XY0 Sets VX to the value of VY
self.v[x] = self.v[y];
self.pc += 2;
}
0x0001 => {
// 0x8XY1 Sets VX to VX or VY. (Bitwise OR operation)
self.v[x] = (self.v[x] | self.v[y]);
self.pc += 2;
}
0x0002 => {
// 0x8XY2 Sets VX to VX and VY. (Bitwise AND operation)
self.v[x] = (self.v[x] & self.v[y]);
self.pc += 2;
}
0x0003 => {
// 0x8XY3 Sets VX to VX xor VY
self.v[x] = (self.v[x] ^ self.v[y]);
self.pc += 2;
}
0x0004 => {
// 0x8XY4 Adds VY to VX. VF is set to 1 when there's a
// carry, and to 0 when there isn't
if self.v[y] > (0xFF - self.v[x]) {
self.v[0xF] = 1;
} else {
self.v[0xF] = 0;
}
self.v[x] += self.v[y];
self.pc += 2;
}
0x0005 => {
// 0x8XY5 VY is subtracted from VX. VF is set to 0 when
// there's a borrow, and 1 when there isn't
if self.v[x] > self.v[y] {
self.v[0xF] = 1;
} else {
self.v[0xF] = 0;
}
self.v[x] -= self.v[y];
self.pc += 2;
}
0x0006 => {
// 0x8XY6 Stores the least significant bit of VX in VF
// and then shifts VX to the right by 1
if self.opcode & 0x1 >= 1 {
self.v[0xF] = 1;
} else {
self.v[0xF] = 0;
}
self.v[x] = self.v[x] >> 1;
self.pc += 2;
}
0x0007 => {
// 0x8XY7 Sets VX to VY minus VX. VF is set to 0 when
// there's a borrow, and 1 when there isn't
if self.v[y] > self.v[x] {
self.v[0xF] = 1;
} else {
self.v[0xF] = 0;
}
self.v[x] = self.v[y] - self.v[x];
self.pc += 2;
}
0x000E => {
// 0x8XYE Stores the most significant bit of VX in VF
// and then shifts VX to the left by 1
if self.opcode & 0x80 == 0x80 {
self.v[0xF] = 1;
} else {
self.v[0xF] = 0;
}
self.v[x] = self.v[x] << 1;
self.pc += 2;
}
_ => println!("unk {:x}", self.opcode),
}
}
0x9000 => {
// 9XY0 Skips the next instruction if VX doesn't equal VY.
// (Usually the next instruction is a jump to skip a code
// block)
if self.v[x] != self.v[y] {
self.pc += 2;
}
self.pc += 2;
}
0xA000 => {
// ANNN set index to NNN position
self.index = nnn;
self.pc += 2;
}
0xB000 => {
// BNNN Jumps to the address NNN plus V0
self.pc = nnn + self.v[0] as u16;
self.pc += 2;
}
0xC000 => {
// CXNN Sets VX to the result of a bitwise and operation on a
// random number (Typically: 0 to 255) and NN
let mut rng = rand::thread_rng();
let r: u8 = rng.gen_range(0, 255);
self.v[x] = r & nn;
self.pc += 2;
}
0xD000 => {
// DXYN Draws a sprite at coordinate (VX, VY) that has a width
// of 8 pixels and a height of N+1 pixels. Each row of 8 pixels
// is read as bit-coded starting from memory location I; I
// value doesn’t change after the execution of this
// instruction. As described above, VF is set to 1 if any
// screen pixels are flipped from set to unset when the sprite
// is drawn, and to 0 if that doesn’t happen
let heigh = self.opcode & 0x000F;
let mut pixel: u8;
self.v[0xF] = 0;
for yline in 0..heigh {
pixel = self.memory[(self.index + yline) as usize];
for xline in 0..8 {
if (pixel & (0x80 >> xline)) != 0 {
let pos = (self.v[x] as u16 + xline) as usize
+ (self.v[y] as u16 + yline) as usize * w;
if pos >= 2048 {
break;
}
if self.gfx[pos] == 1 {
self.v[0xF] = 1;
} else {
self.v[0xF] ^= 1;
}
}
}
}
self.draw_flag = true;
self.pc += 2;
}
0xE000 => {
match self.opcode & 0x00FF {
0x009E => {
// EX9E Skips the next instruction if the key stored in
// VX is pressed. (Usually the next instruction is a
// jump to skip a code block)
if self.key[self.v[x] as usize] != 0 {
self.pc += 2;
}
self.pc += 2;
}
0x00A1 => {
// EXA1 Skips the next instruction if the key stored in
// VX isn't pressed. (Usually the next instruction is a
// jump to skip a code block)
if self.key[self.v[x] as usize] != 1 {
self.pc += 2;
}
self.pc += 2;
}
_ => println!("unk {:x}", self.opcode),
}
}
0xF000 => {
match self.opcode & 0x00FF {
0x0007 => {
// FX07 Sets VX to the value of the delay timer
self.v[x] = self.delay_timer;
self.pc += 2;
}
0x000A => {
// FX0A A key press is awaited, and then stored in VX.
// (Blocking Operation. All instruction halted until
// next key event)
let mut pressed: bool = false;
for i in 0..16 {
if self.key[i] == 1 {
self.v[x] = i as u8;
pressed = true;
}
}
if pressed {
self.pc += 2;
}
}
0x0015 => {
// FX15 Sets the delay timer to VX
self.delay_timer = self.v[x];
self.pc += 2;
}
0x0018 => {
// FX18 Sets the sound timer to VX
self.sound_timer = self.v[x];
self.pc += 2;
}
0x001E => {
// FX1E Adds VX to I. VF is not affected
self.index += self.v[x] as u16;
self.pc += 2;
}
0x0029 => {
// FX29 Sets I to the location of the sprite for the
// character in VX. Characters 0-F (in hexadecimal) are
// represented by a 4x5 font
self.index = self.v[x] as u16 * 5;
self.pc += 2;
}
0x0033 => {
self.memory[self.index as usize] = self.v[x] / 100;
self.memory[self.index as usize + 1] = (self.v[x] / 10) % 10;
self.memory[self.index as usize + 2] = (self.v[x] / 100) % 10;
self.pc += 2;
}
0x0055 => {
// FX55 Stores V0 to VX (including VX) in memory
// starting at address I. The offset from I is
// increased by 1 for each value written, but I itself
// is left unmodified
for i in 0..(x + 1) {
self.memory[self.index as usize + i] = self.v[i];
}
self.pc += 2;
}
0x0064 => {
// 0xFX65 Fills V0 to VX (including VX) with values
// from memory starting at address I. The offset from I
// is increased by 1 for each value written, but I
// itself is left unmodified
for i in 0..(x + 1) {
self.v[i] = self.memory[self.index as usize + i];
}
self.pc += 2;
}
_ => println!("unk {:x}", self.opcode),
}
}
_ => println!("opc {:x}", self.opcode),
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_load_game() {
let mut c = Chip8::new();
c.load_game("Cargo.toml");
c.emulate_cycle();
}
}
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