1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
|
const HALT: u8 = 0x0;
const ARITHMETIC_AND_LOGIC: u8 = 0x8;
const ADD_XY: u8 = 0x4;
struct CPU {
// current_operation: u16, // no longer needed
registers: [u8; 16], // increase number of registers to 16 (0..F), as per CHIP-8
position_in_memory: usize, // add a program counter.. using a usize to simplify array indexing
memory: [u8; 4096], // give the system 4kb memory
}
impl CPU {
fn run(&mut self) {
loop {
let op_byte1 = self.memory[self.position_in_memory] as u16; //
let op_byte2 = self.memory[self.position_in_memory + 1] as u16; //
let raw_op = op_byte1 << 8 | op_byte2;
self.position_in_memory += 2;
let op_major = ((raw_op & 0xF000) >> 12) as u8;
let x = ((raw_op & 0x0F00) >> 8) as u8;
let y = ((raw_op & 0x00F0) >> 4) as u8;
let op_minor = (raw_op & 0x000F) as u8;
match (op_major, op_minor) {
(HALT, HALT) => { return; },
(ARITHMETIC_AND_LOGIC, ADD_XY) => self.add_xy(x, y),
_ => unimplemented!("opcode {:04x}", raw_op), // this macro is useful when you are debugging, as it will promptly indicate that you have made a typo
}
}
}
fn add_xy(&mut self, x: u8, y: u8) {
self.registers[x as usize] += self.registers[y as usize];
}
}
fn main() {
let mut cpu = CPU {
registers: [0; 16],
memory: [0; 4096],
position_in_memory: 0,
};
cpu.registers[0] = 5;
cpu.registers[1] = 10;
cpu.registers[2] = 10; // initialise a few more registers
cpu.registers[3] = 10; //
cpu.memory[0] = 0x80; cpu.memory[1] = 0x14; // 0x8014 -> ADD register 1 to register 0
cpu.memory[2] = 0x80; cpu.memory[3] = 0x24; // 0x8014 -> ADD register 2 to register 0
cpu.memory[4] = 0x80; cpu.memory[5] = 0x34; // 0x8014 -> ADD register 3 to register 0
cpu.run();
assert_eq!(cpu.registers[0], 35);
println!("5 + 10 + 10 + 10 = {}", cpu.registers[0]);
}
|
