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|
use crate::instructions::Instruction;
use crate::memory::Memory;
#[derive(Default, Debug)]
#[allow(dead_code)]
pub struct CPU {
pub a: u8,
pub b: u8,
pub c: u8,
pub d: u8,
pub pc: u16,
pub sp: u16,
pub zero: bool,
pub carry: bool,
pub halted: bool,
}
impl CPU {
fn push16(&mut self, mem: &mut Memory, val: u16) {
self.dec_sp();
mem.write(self.sp, (val >> 8) as u8); // high
self.dec_sp();
mem.write(self.sp, (val & 0xFF) as u8); // low
}
fn pop16(&mut self, mem: &mut Memory) -> u16 {
let low = mem.read(self.sp) as u16;
self.inc_sp();
let high = mem.read(self.sp) as u16;
self.inc_sp();
(high << 8) | low
}
pub fn debug_instr(&self, mem: &Memory) {
let opcode = mem.read(self.pc);
println!(
"PC={:04X} {:<3} | A={:02X} B={:02X} C={:02X} D={:02X} | Z={} C={}",
self.pc,
Instruction::opcode_name(opcode),
self.a,
self.b,
self.c,
self.d,
self.zero as u8,
self.carry as u8
);
}
pub fn step(&mut self, mem: &mut Memory) {
let opcode = mem.read(self.pc);
self.inc_pc();
match opcode {
x if x == Instruction::MOV_RI as u8 => self.mov_ri(mem),
x if x == Instruction::MOV_RR as u8 => self.mov_rr(mem),
x if x == Instruction::ADD_RR as u8 => self.add_rr(mem),
x if x == Instruction::ADD_RI as u8 => self.add_ri(mem),
x if x == Instruction::SUB_RR as u8 => self.sub_rr(mem),
x if x == Instruction::SUB_RI as u8 => self.sub_ri(mem),
x if x == Instruction::JMP as u8 => self.jmp(mem),
x if x == Instruction::JZ as u8 => self.jz(mem),
x if x == Instruction::JNZ as u8 => self.jnz(mem),
x if x == Instruction::CMP_RI as u8 => self.cmp_ri(mem),
x if x == Instruction::CMP_RR as u8 => self.cmp_rr(mem),
x if x == Instruction::MUL as u8 => self.mul(mem),
x if x == Instruction::DIV as u8 => self.div(mem),
x if x == Instruction::CALL as u8 => self.call(mem),
x if x == Instruction::RET as u8 => self.ret(mem),
x if x == Instruction::SYS as u8 => self.syscall(mem),
x if x == Instruction::HLT as u8 => self.halt(),
_ => panic!("Unknown opcode {:02X}", opcode),
}
}
pub fn inc_pc(&mut self) {
self.pc += 1;
}
pub fn inc_sp(&mut self) {
self.sp = self.sp.wrapping_add(1);
}
pub fn dec_sp(&mut self) {
self.sp = self.sp.wrapping_sub(1);
}
pub fn halt(&mut self) {
self.halted = true;
}
pub fn mov_ri(&mut self, mem: &Memory) {
let reg = mem.read(self.pc);
self.inc_pc();
let val = mem.read(self.pc);
self.inc_pc();
match reg {
0 => self.a = val,
1 => self.b = val,
2 => self.c = val,
3 => self.d = val,
_ => {}
}
self.zero = val == 0;
}
pub fn mov_rr(&mut self, mem: &Memory) {
let dest = mem.read(self.pc);
self.inc_pc();
let src= mem.read(self.pc);
self.inc_pc();
let val = self.get_reg(src);
self.set_reg(dest, val);
self.zero = val == 0;
}
pub fn add_rr(&mut self, mem: &Memory) {
let dest = mem.read(self.pc);
self.pc += 1;
let src = mem.read(self.pc);
self.pc += 1;
let (result, carry) = match (dest, src) {
(0, 0) => self.a.overflowing_add(self.a),
(0, 1) => self.a.overflowing_add(self.b),
(0, 2) => self.a.overflowing_add(self.c),
(0, 3) => self.a.overflowing_add(self.d),
(1, 0) => self.b.overflowing_add(self.a),
(1, 1) => self.b.overflowing_add(self.b),
(1, 2) => self.b.overflowing_add(self.c),
(1, 3) => self.b.overflowing_add(self.d),
(2, 0) => self.c.overflowing_add(self.a),
(2, 1) => self.c.overflowing_add(self.b),
(2, 2) => self.c.overflowing_add(self.c),
(2, 3) => self.c.overflowing_add(self.d),
(3, 0) => self.d.overflowing_add(self.a),
(3, 1) => self.d.overflowing_add(self.b),
(3, 2) => self.d.overflowing_add(self.c),
(3, 3) => self.d.overflowing_add(self.d),
_ => (0, false),
};
match dest {
0 => self.a = result,
1 => self.b = result,
2 => self.c = result,
3 => self.d = result,
_ => {}
}
self.zero = result == 0;
self.carry = carry;
}
pub fn add_ri(&mut self, mem: &Memory) {
let dest = mem.read(self.pc);
self.pc += 1;
let imm = mem.read(self.pc);
self.pc += 1;
let (result, carry) = match dest {
0 => self.a.overflowing_add(imm),
1 => self.b.overflowing_add(imm),
2 => self.c.overflowing_add(imm),
3 => self.d.overflowing_add(imm),
_ => (0, false),
};
match dest {
0 => self.a = result,
1 => self.b = result,
2 => self.c = result,
3 => self.d = result,
_ => {}
}
self.zero = result == 0;
self.carry = carry;
}
pub fn sub_rr(&mut self, mem: &Memory) {
let dest = mem.read(self.pc);
self.pc += 1;
let src = mem.read(self.pc);
self.pc += 1;
let (result, borrow) = match (dest, src) {
(0, 0) => self.a.overflowing_sub(self.a),
(0, 1) => self.a.overflowing_sub(self.b),
(0, 2) => self.a.overflowing_sub(self.c),
(0, 3) => self.a.overflowing_sub(self.d),
(1, 0) => self.b.overflowing_sub(self.a),
(1, 1) => self.b.overflowing_sub(self.b),
(1, 2) => self.b.overflowing_sub(self.c),
(1, 3) => self.b.overflowing_sub(self.d),
(2, 0) => self.c.overflowing_sub(self.a),
(2, 1) => self.c.overflowing_sub(self.b),
(2, 2) => self.c.overflowing_sub(self.c),
(2, 3) => self.c.overflowing_sub(self.d),
(3, 0) => self.d.overflowing_sub(self.a),
(3, 1) => self.d.overflowing_sub(self.b),
(3, 2) => self.d.overflowing_sub(self.c),
(3, 3) => self.d.overflowing_sub(self.d),
_ => (0, false),
};
match dest {
0 => self.a = result,
1 => self.b = result,
2 => self.c = result,
3 => self.d = result,
_ => {}
}
self.zero = result == 0;
self.carry = borrow;
}
pub fn sub_ri(&mut self, mem: &Memory) {
let dest = mem.read(self.pc);
self.pc += 1;
let imm = mem.read(self.pc);
self.pc += 1;
let (result, borrow) = match dest {
0 => self.a.overflowing_sub(imm),
1 => self.b.overflowing_sub(imm),
2 => self.c.overflowing_sub(imm),
3 => self.d.overflowing_sub(imm),
_ => (0, false),
};
match dest {
0 => self.a = result,
1 => self.b = result,
2 => self.c = result,
3 => self.d = result,
_ => {}
}
self.zero = result == 0;
self.carry = borrow;
}
pub fn jmp(&mut self, mem: &Memory) {
let low = mem.read(self.pc) as u16;
self.inc_pc();
let high = mem.read(self.pc) as u16;
self.inc_pc();
let addrs = (high << 8) | low;
self.pc = addrs;
}
pub fn jz(&mut self, mem: &Memory) {
let low = mem.read(self.pc) as u16;
self.inc_pc();
let high = mem.read(self.pc) as u16;
self.inc_pc();
let addrs = (high << 8) | low;
if self.zero {
self.pc = addrs;
}
}
pub fn jnz(&mut self, mem: &Memory) {
let low = mem.read(self.pc) as u16;
self.inc_pc();
let high = mem.read(self.pc) as u16;
self.inc_pc();
let addrs = (high << 8) | low;
if !self.zero {
self.pc = addrs;
}
}
pub fn cmp_rr(&mut self, mem: &Memory) {
let r1 = mem.read(self.pc);
self.inc_pc();
let r2 = mem.read(self.pc);
self.inc_pc();
let v1 = self.get_reg(r1);
let v2 = self.get_reg(r2);
let (result, borrow) = v1.overflowing_sub(v2);
self.zero = result == 0;
self.carry = borrow;
}
pub fn cmp_ri(&mut self, mem: &Memory) {
let r1 = mem.read(self.pc);
self.inc_pc();
let r2 = mem.read(self.pc);
self.inc_pc();
let v1 = self.get_reg(r1);
let (result, borrow) = v1.overflowing_sub(r2);
self.zero = result == 0;
self.carry = borrow;
}
pub fn mul(&mut self, mem: &Memory) {
let dest = mem.read(self.pc); self.inc_pc();
let src = mem.read(self.pc); self.inc_pc();
let lhs = self.get_reg(dest);
let rhs = self.get_reg(src);
let result16 = (lhs as u16) * (rhs as u16);
let result8 = (result16 & 0xFF) as u8;
self.set_reg(dest, result8);
self.zero = result8 == 0;
self.carry = result16 > 0xFF;
}
pub fn div(&mut self, mem: &Memory) {
let dest = mem.read(self.pc); self.inc_pc();
let src = mem.read(self.pc); self.inc_pc();
let lhs = self.get_reg(dest);
let rhs = self.get_reg(src);
if rhs == 0 {
panic!("Division by zero");
// OR: set halted = true
// OR: define a syscall/exception later
}
let result = lhs / rhs;
self.set_reg(dest, result);
self.zero = result == 0;
// carry unchanged
}
pub fn call(&mut self, mem: &mut Memory ) {
let low = mem.read(self.pc) as u16; self.inc_pc();
let high = mem.read(self.pc) as u16; self.inc_pc();
let addr = (high << 8) | low;
let return_addr = self.pc;
self.push16(mem, return_addr);
self.pc = addr;
}
pub fn ret(&mut self, mem: &mut Memory) {
let addr = self.pop16(mem);
self.pc = addr;
}
pub fn syscall(&mut self, mem: &Memory) {
let num = mem.read(self.pc);
self.pc = self.pc.wrapping_add(1);
match num {
0 => {
// exit
self.halted = true;
}
1 => {
// print A as number
println!("{}", self.a);
}
2 => {
// print A as ASCII char
print!("{}", self.a as char);
}
_ => panic!("Unknown syscall {}", num),
}
}
fn get_reg(&self, r: u8) -> u8 {
match r {
0 => self.a,
1 => self.b,
2 => self.c,
3 => self.d,
_ => panic!("Invalid Register"),
}
}
fn set_reg(&mut self, dest: u8, val: u8) {
match dest {
0 => self.a = val,
1 => self.b = val,
2 => self.c = val,
3 => self.d = val,
_ => panic!("Invalid register"),
}
}
}
|
