| 1 | use crate::instructions::Instruction; |
| 2 | use crate::memory::Memory; |
| 3 | |
| 4 | #[derive(Default, Debug)] |
| 5 | pub struct CPU { |
| 6 | pub a: u8, |
| 7 | pub b: u8, |
| 8 | pub c: u8, |
| 9 | pub d: u8, |
| 10 | |
| 11 | pub pc: u16, |
| 12 | pub sp: u16, |
| 13 | |
| 14 | pub zero: bool, |
| 15 | pub carry: bool, |
| 16 | |
| 17 | pub halted: bool, |
| 18 | } |
| 19 | |
| 20 | impl CPU { |
| 21 | pub fn step(&mut self, mem: &mut Memory) { |
| 22 | let opcode = mem.read(self.pc); |
| 23 | self.inc_pc(); |
| 24 | |
| 25 | match opcode { |
| 26 | x if x == Instruction::MOV as u8 => self.mov(mem), |
| 27 | x if x == Instruction::ADD as u8 => self.add(mem), |
| 28 | x if x == Instruction::SUB as u8 => self.sub(mem), |
| 29 | x if x == Instruction::JMP as u8 => self.jmp(mem), |
| 30 | x if x == Instruction::JZ as u8 => self.jz(mem), |
| 31 | x if x == Instruction::JNZ as u8 => self.jnz(mem), |
| 32 | x if x == Instruction::HLT as u8 => self.halt(), |
| 33 | _ => panic!("Unknown opcode {:02X}", opcode), |
| 34 | } |
| 35 | } |
| 36 | |
| 37 | pub fn inc_pc(&mut self) { |
| 38 | self.pc += 1; |
| 39 | } |
| 40 | |
| 41 | pub fn halt(&mut self) { |
| 42 | self.halted = true; |
| 43 | } |
| 44 | |
| 45 | pub fn mov(&mut self, mem: &Memory) { |
| 46 | let reg = mem.read(self.pc); |
| 47 | self.inc_pc(); |
| 48 | let val = mem.read(self.pc); |
| 49 | self.inc_pc(); |
| 50 | |
| 51 | match reg { |
| 52 | 0 => self.a = val, |
| 53 | 1 => self.b = val, |
| 54 | 2 => self.c = val, |
| 55 | 3 => self.d = val, |
| 56 | _ => {} |
| 57 | } |
| 58 | |
| 59 | self.zero = val == 0; |
| 60 | } |
| 61 | |
| 62 | pub fn add(&mut self, mem: &Memory) { |
| 63 | let dest = mem.read(self.pc); |
| 64 | self.pc += 1; |
| 65 | let src = mem.read(self.pc); |
| 66 | self.pc += 1; |
| 67 | |
| 68 | let (result, carry) = match (dest, src) { |
| 69 | (0, 0) => self.a.overflowing_add(self.a), |
| 70 | (0, 1) => self.a.overflowing_add(self.b), |
| 71 | (0, 2) => self.a.overflowing_add(self.c), |
| 72 | (0, 3) => self.a.overflowing_add(self.d), |
| 73 | |
| 74 | (1, 0) => self.b.overflowing_add(self.a), |
| 75 | (1, 1) => self.b.overflowing_add(self.b), |
| 76 | (1, 2) => self.b.overflowing_add(self.c), |
| 77 | (1, 3) => self.b.overflowing_add(self.d), |
| 78 | |
| 79 | (2, 0) => self.c.overflowing_add(self.a), |
| 80 | (2, 1) => self.c.overflowing_add(self.b), |
| 81 | (2, 2) => self.c.overflowing_add(self.c), |
| 82 | (2, 3) => self.c.overflowing_add(self.d), |
| 83 | |
| 84 | (3, 0) => self.d.overflowing_add(self.a), |
| 85 | (3, 1) => self.d.overflowing_add(self.b), |
| 86 | (3, 2) => self.d.overflowing_add(self.c), |
| 87 | (3, 3) => self.d.overflowing_add(self.d), |
| 88 | |
| 89 | _ => (0, false), |
| 90 | }; |
| 91 | |
| 92 | match dest { |
| 93 | 0 => self.a = result, |
| 94 | 1 => self.b = result, |
| 95 | 2 => self.c = result, |
| 96 | 3 => self.d = result, |
| 97 | _ => {} |
| 98 | } |
| 99 | |
| 100 | self.zero = result == 0; |
| 101 | self.carry = carry; |
| 102 | } |
| 103 | |
| 104 | pub fn sub(&mut self, mem: &Memory) { |
| 105 | let dest = mem.read(self.pc); |
| 106 | self.pc += 1; |
| 107 | let src = mem.read(self.pc); |
| 108 | self.pc += 1; |
| 109 | |
| 110 | let (result, borrow) = match (dest, src) { |
| 111 | (0, 0) => self.a.overflowing_sub(self.a), |
| 112 | (0, 1) => self.a.overflowing_sub(self.b), |
| 113 | (0, 2) => self.a.overflowing_sub(self.c), |
| 114 | (0, 3) => self.a.overflowing_sub(self.d), |
| 115 | |
| 116 | (1, 0) => self.b.overflowing_sub(self.a), |
| 117 | (1, 1) => self.b.overflowing_sub(self.b), |
| 118 | (1, 2) => self.b.overflowing_sub(self.c), |
| 119 | (1, 3) => self.b.overflowing_sub(self.d), |
| 120 | |
| 121 | (2, 0) => self.c.overflowing_sub(self.a), |
| 122 | (2, 1) => self.c.overflowing_sub(self.b), |
| 123 | (2, 2) => self.c.overflowing_sub(self.c), |
| 124 | (2, 3) => self.c.overflowing_sub(self.d), |
| 125 | |
| 126 | (3, 0) => self.d.overflowing_sub(self.a), |
| 127 | (3, 1) => self.d.overflowing_sub(self.b), |
| 128 | (3, 2) => self.d.overflowing_sub(self.c), |
| 129 | (3, 3) => self.d.overflowing_sub(self.d), |
| 130 | |
| 131 | _ => (0, false), |
| 132 | }; |
| 133 | |
| 134 | match dest { |
| 135 | 0 => self.a = result, |
| 136 | 1 => self.b = result, |
| 137 | 2 => self.c = result, |
| 138 | 3 => self.d = result, |
| 139 | _ => {} |
| 140 | } |
| 141 | |
| 142 | self.zero = result == 0; |
| 143 | self.carry = borrow; |
| 144 | } |
| 145 | |
| 146 | pub fn jmp(&mut self, mem: &Memory) { |
| 147 | let low = mem.read(self.pc) as u16; |
| 148 | self.inc_pc(); |
| 149 | let high = mem.read(self.pc) as u16; |
| 150 | self.inc_pc(); |
| 151 | |
| 152 | let addrs = (high << 8) | low; |
| 153 | |
| 154 | self.pc = addrs; |
| 155 | } |
| 156 | |
| 157 | pub fn jz(&mut self, mem: &Memory) { |
| 158 | let low = mem.read(self.pc) as u16; |
| 159 | self.inc_pc(); |
| 160 | let high = mem.read(self.pc) as u16; |
| 161 | self.inc_pc(); |
| 162 | |
| 163 | let addrs = (high << 8) | low; |
| 164 | |
| 165 | if self.zero { |
| 166 | self.pc = addrs; |
| 167 | } |
| 168 | } |
| 169 | |
| 170 | pub fn jnz(&mut self, mem: &Memory) { |
| 171 | let low = mem.read(self.pc) as u16; |
| 172 | self.inc_pc(); |
| 173 | let high = mem.read(self.pc) as u16; |
| 174 | self.inc_pc(); |
| 175 | |
| 176 | let addrs = (high << 8) | low; |
| 177 | |
| 178 | if !self.zero { |
| 179 | self.pc = addrs; |
| 180 | } |
| 181 | } |
| 182 | } |