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This commit is contained in:
Miguel Angel 2024-09-03 15:08:02 +02:00
parent 7a9bfc4c79
commit 25d652b173
1 changed files with 140 additions and 5 deletions
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145
src/cpu.ts
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@ -101,15 +101,150 @@ class CPU {
private cycle() { private cycle() {
// Fetch opcode // Fetch opcode
let firstOpcode: number = this.memory[this.pc]; let firstOpcode: number = this.memory[this.pc];
let secondtOpcode: number = this.memory[this.pc + 1]; let secondOpcode: number = this.memory[this.pc + 1];
let opcode: number = firstOpcode << 8 | secondtOpcode; let opcode: number = firstOpcode << 8 | secondOpcode;
// Decode opcode // Decode opcode
// X000
let firstNibble = opcode >> 12; let firstNibble = firstOpcode >> 4;
switch(firstNibble) { switch(firstNibble) {
case 0x0:
if(opcode == 0x00E0) {
// Clear the screen
this.clearDisplay();
}else if(opcode == 0x00EE) {
// Returns from a subroutine
this.stackPointer--;
this.pc = this.stack[this.pc];
}
this.incrementPC();
break;
case 0x1:
// goto NNN;
let threeNib = opcode & 0x0FFF;
this.pc = threeNib;
break;
case 0x2:
// Calls subroutine at NNN
this.stack[this.stackPointer] = this.pc; // Store PC at stack
this.stackPointer++; // Increment it
this.pc = opcode & 0x0FFF; // Go to that address to execute code
break;
case 0x3: {
// 3XNN
// Skips the next instruction if VX equals NN
let secondNibble = firstOpcode & 0xF; //0X00
let val = opcode & 0x00FF; //0x00NN
if(this.registers[secondNibble] == val){
this.incrementPC();
}
this.incrementPC();
}
break;
case 0x4: {
// 4XNN
// Skips the next instruction if VX NOT equals NN
let secondNibble = firstOpcode & 0xF; //0X00
let val = opcode & 0x00FF; //0x00NN
if(this.registers[secondNibble] != val){
this.incrementPC();
}
this.incrementPC();
}
break;
case 0x5: {
// 5XY0
// Skips the next instruction if VX == VY
let secondNibble = firstOpcode & 0xF; //0X00
let thirdNibble = secondOpcode >> 4; //00Y0
if(this.registers[secondNibble] == this.registers[thirdNibble]) {
this.incrementPC();
}
this.incrementPC();
}
break;
case 0x6: {
// 6XNN
// Sets VX to NN
let secondNibble = firstOpcode & 0xF; //0X00
this.registers[secondNibble] = secondOpcode;
this.incrementPC();
}
break;
case 0x7: {
// 7XNN
// Adds NN to VX
let secondNibble = firstOpcode & 0xF; //0X00
this.registers[secondNibble] = secondOpcode;
this.incrementPC();
}
break;
case 0x8: {
let secondNibble = firstOpcode & 0xF; //0X00
let thirdNibble = secondOpcode >> 4; //00Y0
let lastNibble = secondOpcode & 0xF; //000N
if(lastNibble == 0x0) {
// 8XY0
// Vx |= Vy
this.registers[secondNibble] = this.registers[thirdNibble];
this.incrementPC();
}else if(lastNibble == 0x1) {
// 8XY1
// Vx |= Vy
this.registers[secondNibble] |= this.registers[thirdNibble];
this.incrementPC();
}else if(lastNibble == 0x2) {
// 8XY2
// Vx &= Vy
this.registers[secondNibble] &= this.registers[thirdNibble];
this.incrementPC();
}else if(lastNibble == 0x3) {
// 8XY3
// Vx ^= Vy
this.registers[secondNibble] ^= this.registers[thirdNibble];
this.incrementPC();
}else if(lastNibble == 0x4) {
// 8XY4
// Vx += Vy
let sum = this.registers[secondNibble] + this.registers[thirdNibble];
this.registers[0xF] = sum > 255 ? 1 : 0; // Set carry flag
this.registers[secondNibble] = sum & 0xFF; // Get only the first byte
this.incrementPC();
}else if(lastNibble == 0x5) {
// 8XY5
// Vx -= Vy
this.registers[0xF] = this.registers[secondNibble] > this.registers[thirdNibble] ? 1 : 0;
let subs = this.registers[secondNibble] - this.registers[thirdNibble];
this.incrementPC();
}else if(lastNibble == 0x6) {
// 8XY6
// Vx >>= 1
this.registers[secondNibble] >> 1;
this.incrementPC();
}else if(lastNibble == 0x7) {
// 8XY7
// Vx = Vy - Vx
this.registers[0xF] = this.registers[secondNibble] > this.registers[thirdNibble] ? 1 : 0;
let subs = this.registers[secondNibble] - this.registers[thirdNibble];
this.incrementPC();
}else if(lastNibble == 0xE) {
}
}
break;
case 0x9: {
// 9XY0
// Skips the next instruction if VX != VY
let secondNibble = firstOpcode & 0xF; //0X00
let thirdNibble = secondOpcode >> 4; //00Y0
if(this.registers[secondNibble] != this.registers[thirdNibble]) {
this.incrementPC();
}
this.incrementPC();
}
break;
} }
} }