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cpu - Refactor CPU flags -- stop using a bitmask to make them easier to handle

This commit is contained in:
n loewen 2023-08-26 14:34:02 +01:00
parent ddab8f42c4
commit b290eb1568
2 changed files with 65 additions and 60 deletions
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118
cpu.js
View File

@ -10,7 +10,7 @@ const {
const { const {
num2hex, num2hex,
num2bin_4bit, bool2bit,
} = require('./logging.js'); } = require('./logging.js');
const display = require('./display.js'); const display = require('./display.js');
@ -19,8 +19,8 @@ const CPU = {
// Core state // Core state
running: false, running: false,
IP: INITIAL_IP_ADDRESS, IP: INITIAL_IP_ADDRESS,
FLAGS: 0, // A bit field! 0000 = ONZC FLAGS: {'C': false, 'Z': false, 'N': false, 'O': false},
FlagNames: ['C', 'Z', 'N', 'O'], FLAGNUMS2NAMES: {0: 'C', 1: 'Z', 2: 'N', 3: 'O'},
Acc: 0, Acc: 0,
memory: null, memory: null,
@ -38,24 +38,8 @@ const CPU = {
CPU.previousIP = CPU.IP; CPU.previousIP = CPU.IP;
CPU.IP = address; CPU.IP = address;
}, },
setFlagOverflow: () => { CPU.FLAGS |= 4 }, updateFlagZero: () => { CPU.FLAGS.Z = CPU.Acc === 0; },
setFlagNegative: () => { CPU.FLAGS |= 4 }, updateFlagNegative: () => { CPU.Acc & 128 ? CPU.FLAGS.N = true : CPU.FLAGS.N = false },
setFlagZero: () => { CPU.FLAGS |= 2 },
setFlagCarry: () => { CPU.FLAGS |= 1 },
unsetFlagOverflow: () => { CPU.FLAGS &= ~8 },
unsetFlagNegative: () => { CPU.FLAGS &= ~4 },
unsetFlagZero: () => { CPU.FLAGS &= ~2 },
unsetFlagCarry: () => { CPU.FLAGS &= ~1 },
updateFlagZero: () => {
if (CPU.Acc === 0) {
CPU.setFlagZero();
} else {
CPU.unsetFlagZero();
}
},
updateFlagNegative: () => {
CPU.Acc & 128 ? CPU.setFlagNegative : CPU.unsetFlagNegative
},
// Debug info // Debug info
previousIP: 0, previousIP: 0,
@ -110,19 +94,22 @@ const Instructions = {
// Calculate sum // Calculate sum
let sum = CPU.Acc + lit; let sum = CPU.Acc + lit;
if (sum > 255) { if (sum > 255) {
CPU.setFlagCarry(); CPU.FLAGS.C = true;
sum = (sum % 255) - 1; sum = (sum % 255) - 1;
} else { } else {
CPU.unsetFlagCarry(); CPU.FLAGS.C = false;
} }
// Calculate overflow flag status // Calculate overflow flag status
let bitSixCarry = 0; let bitSixCarry = 0;
if ((CPU.Acc & 64) && (lit & 64)) { bitSixCarry = 1; } if ((CPU.Acc & 64) && (lit & 64)) { bitSixCarry = 1; }
let overflow = bitSixCarry ^ (CPU.FLAGS & 8); // let overflow = bitSixCarry ^ (CPU.FLAGS & 8);
// FIXME FIXME FIXME
// I'm on a plane and can't remember how this works
let overflow = 0;
if (overflow) { if (overflow) {
CPU.setFlagOverflow(); CPU.FLAGS.O = true;
} else { } else {
CPU.unsetFlagOverflow(); CPU.FLAGS.O = false;
} }
CPU.Acc = sum; CPU.Acc = sum;
CPU.updateFlagNegative(); CPU.updateFlagNegative();
@ -135,19 +122,22 @@ const Instructions = {
// Calculate sum // Calculate sum
let sum = CPU.Acc + CPU.memory[addr]; let sum = CPU.Acc + CPU.memory[addr];
if (sum > 255) { if (sum > 255) {
CPU.setFlagCarry(); CPU.FLAGS.C = true;
sum = (sum % 255) - 1; sum = (sum % 255) - 1;
} else { } else {
CPU.unsetFlagCarry(); CPU.FLAGS.C = false;
} }
// Calculate overflow flag status // Calculate overflow flag status
let bitSixCarry = 0; let bitSixCarry = 0;
if ((CPU.Acc & 64) && (addr & 64)) { bitSixCarry = 1; } if ((CPU.Acc & 64) && (addr & 64)) { bitSixCarry = 1; }
let overflow = bitSixCarry ^ (CPU.FLAGS & 8); // let overflow = bitSixCarry ^ (CPU.FLAGS & 8);
// FIXME FIXME FIXME
// I'm on a plane and can't remember how this works
let overflow = 0;
if (overflow) { if (overflow) {
CPU.setFlagOverflow(); CPU.FLAGS.O = true;
} else { } else {
CPU.unsetFlagOverflow(); CPU.FLAGS.O = false;
} }
CPU.Acc = sum; CPU.Acc = sum;
CPU.updateFlagNegative(); CPU.updateFlagNegative();
@ -160,19 +150,22 @@ const Instructions = {
// Calculate sum // Calculate sum
let sum = CPU.Acc - lit; let sum = CPU.Acc - lit;
if (sum < 0) { if (sum < 0) {
CPU.setFlagCarry(); CPU.FLAGS.C = true;
sum = sum + 256; sum = sum + 256;
} else { } else {
CPU.unsetFlagCarry(); CPU.FLAGS.C = false;
} }
// Calculate overflow flag status // Calculate overflow flag status
let bitSixCarry = 0; let bitSixCarry = 0;
if ((CPU.Acc & 64) && (lit & 64)) { bitSixCarry = 1; } if ((CPU.Acc & 64) && (lit & 64)) { bitSixCarry = 1; }
let overflow = bitSixCarry ^ (CPU.FLAGS & 8); // let overflow = bitSixCarry ^ (CPU.FLAGS & 8);
// FIXME FIXME FIXME
// I'm on a plane and can't remember how this works
let overflow = 0;
if (overflow) { if (overflow) {
CPU.setFlagOverflow(); CPU.FLAGS.O = true;
} else { } else {
CPU.unsetFlagOverflow(); CPU.FLAGS.O = false;
} }
CPU.Acc = sum; CPU.Acc = sum;
CPU.updateFlagNegative(); CPU.updateFlagNegative();
@ -185,19 +178,22 @@ const Instructions = {
// Calculate sum // Calculate sum
let sum = CPU.Acc - CPU.memory[addr]; let sum = CPU.Acc - CPU.memory[addr];
if (sum < 0) { if (sum < 0) {
CPU.setFlagCarry(); CPU.FLAGS.C = true;
sum = sum + 256; sum = sum + 256;
} else { } else {
CPU.unsetFlagCarry(); CPU.FLAGS.C = false;
} }
// Calculate overflow flag status // Calculate overflow flag status
let bitSixCarry = 0; let bitSixCarry = 0;
if ((CPU.Acc & 64) && (addr & 64)) { bitSixCarry = 1; } if ((CPU.Acc & 64) && (addr & 64)) { bitSixCarry = 1; }
let overflow = bitSixCarry ^ (CPU.FLAGS & 8); // let overflow = bitSixCarry ^ (CPU.FLAGS & 8);
// FIXME FIXME FIXME
// I'm on a plane and can't remember how this works
let overflow = 0;
if (overflow) { if (overflow) {
CPU.setFlagOverflow(); CPU.FLAGS.O = true;
} else { } else {
CPU.unsetFlagOverflow(); CPU.FLAGS.O = false;
} }
CPU.Acc = sum; CPU.Acc = sum;
CPU.updateFlagNegative(); CPU.updateFlagNegative();
@ -234,26 +230,24 @@ const Instructions = {
}, },
flag_toggle: (flagNum) => { flag_toggle: (flagNum) => {
CPU.currentInstruction.mnemonic = `FTG; ${CPU.FlagNames[flagNum]}`; if (flagNum === null) {
let mask = null; console.error('Invalid flag number');
if (flagNum === 0) { mask = 1; } process.exit();
if (flagNum === 1) { mask = 2; } }
if (flagNum === 2) { mask = 8; } const flagName = CPU.FLAGNUMS2NAMES[flagNum];
if (flagNum === 3) { mask = 16; } CPU.currentInstruction.mnemonic = `FTG ${flagName}`;
if (mask === null) { throw new Error('Invalid flag number'); } CPU.FLAGS[flagName] = !CPU.FLAGS[flagName];
CPU.FLAGS = CPU.FLAGS ^= mask;
CPU.incrementIP(2); CPU.incrementIP(2);
}, },
flag_hop: (flagNum) => { flag_hop: (flagNum) => {
CPU.currentInstruction.mnemonic = `FTG; ${CPU.FlagNames[flagNum]}; IP+2: ${CPU.memory[CPU.IP+2]}, IP+3: ${CPU.memory[CPU.IP+3]}`; if (flagNum === null) {
let mask = null; console.error('Invalid flag number');
if (flagNum === 0) { mask = 1; } process.exit();
if (flagNum === 1) { mask = 2; } }
if (flagNum === 2) { mask = 8; } const flagName = CPU.FLAGNUMS2NAMES[flagNum];
if (flagNum === 3) { mask = 16; } CPU.currentInstruction.mnemonic = `FHP ${flagName}; IP+2: ${CPU.memory[CPU.IP+2]}, IP+3: ${CPU.memory[CPU.IP+3]}`;
if (mask === null) { throw new Error('Invalid flag number'); } if (CPU.FLAGS[CPU.FLAGNUMS2NAMES[flagNum]]) {
if (CPU.FLAGS & mask) {
CPU.incrementIP(4); CPU.incrementIP(4);
} else { } else {
CPU.incrementIP(2); CPU.incrementIP(2);
@ -373,7 +367,11 @@ exports.runProgram =
// Animate the output by pausing between steps // Animate the output by pausing between steps
const loop = setInterval(async () => { const loop = setInterval(async () => {
stepCPU(debugInfo, debug, prettyPrint); stepCPU(debugInfo, debug, prettyPrint);
if (!CPU.running) process.exit(); if (!CPU.running) {
logCPUState(debugInfo, debug, prettyPrint);
console.log('Halted');
process.exit();
}
}, clockSpeed); }, clockSpeed);
} }
}; };
@ -412,12 +410,12 @@ function logCPUState(debugInfo, debug = false, prettyPrintDisplay = false) {
console.log(); console.log();
if (debugInfo) { if (debugInfo) {
console.log(`Line ${debugInfo.lineNumber}: ${debugInfo.source}`); console.log(`Line ${debugInfo.lineNumber}: ${debugInfo.source}`);
console.log(); console.log();
} }
console.log('Mnemonic:', CPU.currentInstruction.mnemonic); console.log('Mnemonic:', CPU.currentInstruction.mnemonic);
console.log(`Machine: $${num2hex(CPU.currentInstruction.opcode)} $${num2hex(CPU.currentInstruction.operand)}`); console.log(`Machine: $${num2hex(CPU.currentInstruction.opcode)} $${num2hex(CPU.currentInstruction.operand)}`);
console.log(); console.log();
console.log(`IP: $${num2hex(CPU.IP)} Acc: $${num2hex(CPU.Acc)} ONZC: ${num2bin_4bit(CPU.FLAGS)}`); console.log(`IP: $${num2hex(CPU.IP)} Acc: $${num2hex(CPU.Acc)} ONZC ${bool2bit(CPU.FLAGS.O)}${bool2bit(CPU.FLAGS.N)}${bool2bit(CPU.FLAGS.Z)}${bool2bit(CPU.FLAGS.C)}`);
console.log(`KEY: $${num2hex(CPU.memory[KEYPAD_ADDR])}  ${CPU.running ? "running" : "halted" }`); console.log(`KEY: $${num2hex(CPU.memory[KEYPAD_ADDR])}  ${CPU.running ? "running" : "halted" }`);
console.log(); console.log();
console.log(); console.log();

7
logging.js
View File

@ -72,6 +72,12 @@ const num2bin_4bit = (num) => (num >>> 0).toString(2).padStart(4, "0");
*/ */
const bin2num = (bin) => parseInt(bin, 2) const bin2num = (bin) => parseInt(bin, 2)
/**
* @param {Boolean} bool
* @returns {0|1}
**/
const bool2bit = (bool) => bool ? 1 : 0;
module.exports = { module.exports = {
"logMemory": logMemory, "logMemory": logMemory,
@ -81,4 +87,5 @@ module.exports = {
"num2bin": num2bin, "num2bin": num2bin,
"num2bin_4bit": num2bin_4bit, "num2bin_4bit": num2bin_4bit,
"bin2num": bin2num, "bin2num": bin2num,
"bool2bit": bool2bit,
} }