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main.js
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function cycle() {
for (let i = 0; i < instructionsPerFrame; i++) {
if (pc < memory.length - 1) {
let firstHalfCurrentInstruction = memory[pc];
let secondHalfCurrentInstruction = memory[pc + 1];
let opcode = firstHalfCurrentInstruction >> 4;
let nnn = ((firstHalfCurrentInstruction & 0x0F) << 8) | secondHalfCurrentInstruction;
let secondNibbleFirstByte = firstHalfCurrentInstruction & 0x0F;
let firstNibbleSecondByte = (secondHalfCurrentInstruction & 0xF0) >> 4;
let secondNibbleSecondByte = secondHalfCurrentInstruction & 0x0F;
switch (opcode) {
case 0: //00e0 (clear screen) or 00ee (return from subroutine)
switch (secondHalfCurrentInstruction) {
case (224):
clearScreen();
break;
case (238):
//returnfrom subroutine 00ee
tmpval = stack[0];
pc = tmpval;
stack.shift();
break;
default:
console.log("Not a valid instruction. Tried to call a thing that started with 0x0, but didn't end in 0xee or 0xe0");
}
break;
case 1: //1nnn
//jump to nnn
pc = nnn;
pc -= 2;
numOfJumps += 2;
break;
case 2: //2nnn
//call subroutine at nnn
//adds the current pc to the start of the stack
stack.unshift(pc);
//jumps to the pointer, minus two, just like in the 1nnn instructions, so that when it gets incremented by two at the end, it is the right one
pc = nnn - 2;
break;
case 3: //3xkk
if (registers[secondNibbleFirstByte].read() == secondHalfCurrentInstruction) {
pc += 2;
}
//skip next instruction if Vx = kk
break;
case 4: //4xkk
if (registers[secondNibbleFirstByte].read() != secondHalfCurrentInstruction) {
pc = pc + 2;
}
break;
case 5: //5xy0
//skip next instruction if Vx = Vy
if (registers[secondNibbleFirstByte].read() == registers[firstNibbleSecondByte].read()) {
pc += 2;
}
break;
case 6: //6xkk
//set Vx to kk
registers[secondNibbleFirstByte].write(secondHalfCurrentInstruction);
break;
case 7: //7xkk
//set Vx = Vx + kk
let pt = registers[secondNibbleFirstByte].read();
let p = secondHalfCurrentInstruction;
tmpval = pt + p;
if(tmpval > 255){
registers[0xf].write(1);
}
tmpval = tmpval % 256;
registers[secondNibbleFirstByte].write(tmpval);
break;
case 8: //8xyn
//lots of math things, not needed initially.
switch (secondNibbleSecondByte) {
case (0): //Vx is set to value of Vy with overflow
registers[secondNibbleFirstByte].write(registers[firstNibbleSecondByte].read());
break;
case (1): //Vx is set to Vx | Vy
registers[secondNibbleFirstByte].write(
registers[secondNibbleFirstByte].read() | registers[firstNibbleSecondByte].read()
);
break;
case (2): //Vx is set to Vx & Vy
registers[secondNibbleFirstByte].write(
registers[secondNibbleFirstByte].read() & registers[firstNibbleSecondByte].read()
);
break;
case (3): //Vx is set to Vx xor Vy
registers[secondNibbleFirstByte].write(
registers[secondNibbleFirstByte].read() ^ registers[firstNibbleSecondByte].read()
);
break;
case (4): //Vx = Vx + Vy, but if overflows over 255, it sets the flag to 1, if not, 0
//Add the value of register VY to register VX
//Set VF to 01 if a carry occurs
//Set VF to 00 if a carry does not
tmpval = registers[secondNibbleFirstByte].read();
tmpval += registers[firstNibbleSecondByte].read();
tmpval = tmpval % 256;
registers[0xf].write(0x00);
if(tmpval > 256){
registers[0xf].write(0x01);
}
registers[secondNibbleFirstByte].write(tmpval);
break;
//LOOK AT MODULUS OF NEGATIVE NUMBERS G4G, IT HAS SOME PSEUDOCODE THAT WILL HELP WITH 5 and 7.
case (5): //Vx = Vx - Vy, if Vx > Vy, vf is 1. if we underflow, vf = 0
tmpval = registers[secondNibbleFirstByte].read() - registers[firstNibbleSecondByte].read();
registers[0xf].write(0x01);
if(tmpval < 0){registers[0xf].write(0x00);}
registers[secondNibbleFirstByte].write(mod(tmpval, 256));
break;
case (6):
if(modern == 1){
registers[secondNibbleFirstByte].write(registers[firstNibbleSecondByte].read());
}
registers[0xf].write(0x00);
tmpval = registers[secondNibbleFirstByte].read() & 0x01;
if(tmpval == 1){registers[0xf].write(0x01);}
registers[secondNibbleFirstByte].write(registers[secondNibbleFirstByte].read() >> 1);
break;
case (7):
//vy - vx
tmpval = registers[firstNibbleSecondByte].read() - registers[secondNibbleFirstByte].read();
registers[0xf].write(0x01);
if(tmpval < 0){registers[0xf].write(0x00);}
registers[secondNibbleFirstByte].write(mod(tmpval, 256));
break;
case (14):
if(modern == 1){
registers[secondNibbleFirstByte].write(registers[firstNibbleSecondByte].read());
}
const shiftedValue = (registers[secondNibbleFirstByte].read() << 1) % 256; // Perform left shift
registers[0xf].write(shiftedValue >> 7); // Set VF based on the shifted-out MSB
registers[secondNibbleFirstByte].write(shiftedValue); // Clear MSB and store the shifted value
break;
default:
console.log("Not a valid instruction!!! Tried to run a command that starts with 8.");
}
break;
case 9: //9xy0
if (registers[secondNibbleFirstByte].read() == registers[firstNibbleSecondByte].read()) {}
else {
pc = pc + 2;
}
break;
case 10: //annn
//sets I to nnn
index.write(nnn);
break;
case 11: //bnnn
//jump to nnn + V0
tmpval = nnn + registers[0x00].read();
pc = tmpval;
pc = pc - 2;
numOfJumps += 2;
break;
case 12: //cxkk
//Set Vx = random byte AND kk
tmpval = randInt(255);
tmpval = tmpval & secondHalfCurrentInstruction;
registers[secondNibbleFirstByte].write(tmpval);
break;
case 13: //dxyn
drawSprite(registers[secondNibbleFirstByte].read(), registers[firstNibbleSecondByte].read(), secondNibbleSecondByte);
break;
case 14: //Ex9e or ExA1, do later
switch(secondHalfCurrentInstruction) {
case 0x9e:
if(registers[secondNibbleFirstByte].read() == key){
pc = pc + 2;
}
break;
case 0xa1:
if(registers[secondNibbleFirstByte].read() != key){
pc = pc + 2;
}
break;
}
break;
case 15: //fx(a hex byte)
switch (secondHalfCurrentInstruction) {
case 0x0A:
if(key != undefined){
registers[secondNibbleFirstByte].write(key);
} else {
pc = pc - 2;
}
break;
case 0x1e: //fx1e set index to index + Vx
index.write(index.read() + registers[secondNibbleFirstByte].read());
break;
case 0x07: //sets Vx to current value of delay timer
registers[secondNibbleFirstByte].write(timer);
break;
case 0x15: //sets delay timer to Vx
timer = registers[secondNibbleFirstByte].read();
break;
case 0x18:
soundTimer = registers[secondNibbleFirstByte].read();
break;
case 0x29:
index.write(memory[(0x50 + ((registers[secondNibbleFirstByte].read() - 1) * 5))]);
break;
case 0x33:
// console.log('ran 0x33');
// memory[index.read()] = parseInt(registers[secondNibbleFirstByte].read() / 100);
// memory[index.read() + 1] = parseInt(registers[secondNibbleFirstByte].read() % 100 / 10);
// memory[index.read() + 2] = registers[secondNibbleFirstByte].read() % 10;
break;
default:
console.log("Not a valid f command.");
console.log(firstHalfCurrentInstruction.toString(16) + secondHalfCurrentInstruction.toString(16));
case 0x55:
// for (let ipn = 0; ipn <= registers[secondNibbleFirstByte].read(); ipn++) {
// memory[index.read() + ipn] = registers[ipn].read();
// }
break;
case 0x65:
// for(let i = 0; i < registers[secondNibbleFirstByte].read() % 16; i++){
// registers[i].write(memory[index.read() + i]);
// if(modern == 0){index.write(index.read() + 1);}
// }
break;
}
break;
default:
console.log("Not a valid instruction");
}
}
else {
console.log("Memory limit reached, stopping loop.");
run = 0;
return;
}
numOfJumps -= 1;
if (numOfJumps < 0) { numOfJumps = 0; }
pc += 2;
}
timer--;
soundTimer--;
if (timer < 0) { timer = 0; }
if (soundTimer < 0) { soundTimer = 0; }
if (soundTimer > 0) {
//make a beeping sound. continuous
}
else {
//stop making noise;
}
if (numOfJumps > maxNumberOfJumps) {
run = 0;
console.log("Jumped more than " + maxNumberOfJumps + " times. Killed process. Change variable maxNumberOfJumps to allow for higher numbers of jumps;");
}
if (run) {
window.requestAnimationFrame(cycle);
}
}
cycle();