Initial proof-of-concept -- a working but incomplete simulator
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n loewen
commit
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# Paper computer simulator experiment
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## ISA
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0 END
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1 STO lit# ; store ... mem[lit#] <- A
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2 STO addr ; store ... mem[mem[addr]] <- A
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3 LDA lit# ; load ... A <- lit#
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4 LDA addr ; load ... A <- mem[addr]
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5 ADD lit# ; add ... A <- A + lit# ... and un/set carry flag
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6 ADD addr ; add ... A <- A + mem[addr] ... and un/set carry flag
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7 SUB lit# ; sub ... A <- A - lit# ... and un/set carry flag
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8 SUB addr ; sub ... A <- A - mem[addr] ... and un/set carry flag
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9 HOP lit# ; skip next instruction if A == lit# ... when true: IP <- PC + 2
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A HOP addr ; skip next instruction if A == addr ... when true: IP <- PC + 2
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B JMP lit# ; ... IP <- lit#
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C JMP addr ; ... IP <- addr
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D CAT ---- ; Carry Flag Toggle ... CF <- !CF
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E CHP ---- ; skip next instruction if Carry Flag is set ... when true: IP <- PC + 2
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F
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### Nice features that didn't fit
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- hop IF< and hop IF>
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- MUL and DIV
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- rotates and shifts
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## Registers
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- A -- accumulator
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- IP -- instruction pointer (aka program counter)
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## Flags
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- CF -- carry flag
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## Memory-mapped peripherals
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- 4x4 display
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- hex keypad (details TBD)
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- ? bank selector (for bank-switching)
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### Maybe someday
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- timer (for a version in software/electronic-hardware)
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## Tentative memory map
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00-0F - display
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10-1F - keypad? (details TBD)
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20 - initial value for IP ?
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21-FF - free
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@ -0,0 +1,131 @@
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function CPU(mem) {
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this.memory = mem;
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this.running = false;
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this.instructionPointer = 0;
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this.carryFlag = 0;
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this.acc = 0;
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this.instructions = {
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end: () => {
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console.log('END');
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this.running = false
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},
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store_lit: (lit) => {
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console.log('STO lit#');
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this.memory[lit] = this.acc;
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log_memory();
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this.instructionPointer = this.instructionPointer += 1;
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},
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store_addr: (addr) => {
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console.log('STO addr');
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this.memory[this.memory[addr]] = this.acc;
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log_memory();
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this.instructionPointer = this.instructionPointer += 1;
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},
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load_lit: (lit) => {
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console.log('LDA lit#');
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this.acc = lit;
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this.instructionPointer = this.instructionPointer += 1;
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},
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load_addr: (addr) => {
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console.log('LDA addr');
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console.log('mem at addr: ', this.memory[addr]);
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this.acc = this.memory[addr];
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this.instructionPointer = this.instructionPointer += 1;
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},
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};
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log_debug_state = () => {
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console.log();
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console.group('CPU state');
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console.log( `IP: ${this.instructionPointer} Acc: ${this.acc} CF: ${this.carryFlag} ${this.running ? "running" : "halted" }` );
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console.log();
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console.groupEnd('CPU state');
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};
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log_memory = () => {
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console.log();
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console.group('Memory');
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console.table(this.memory);
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console.groupEnd('Memory');
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}
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this.perform_operation = (opcode, arg) => {
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switch (opcode) {
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case 0:
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this.instructions.end(arg);
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break;
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case 1:
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this.instructions.store_lit(arg);
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break;
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case 2:
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this.instructions.store_addr(arg);
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break;
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case 3:
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this.instructions.load_lit(arg);
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break;
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case 4:
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this.instructions.load_addr(arg);
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break;
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default:
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console.error( `Invalid opcode: ${opcode} with argument ${arg}` );
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}
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};
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this.run_program = () => {
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console.log();
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console.log( "Running program..." );
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log_debug_state();
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this.running = true;
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for (let i = 1; i < 16; i++) {
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if ( this.running &&
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(this.instructionPointer < this.memory.length) ) {
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let op_arg_tuple = this.memory[this.instructionPointer];
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console.group("Proccessing instruction");
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console.log( op_arg_tuple );
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// console.log( `processing opcode ${op_arg_tuple[0]} with arg ${op_arg_tuple[1]}` );
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this.perform_operation(op_arg_tuple[0], op_arg_tuple[1]);
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log_debug_state();
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console.groupEnd("Processing instruction");
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}
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}
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}
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};
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// UNIMPLEMENTED
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let add_lit = function(lit) { return; }
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let add_addr = function(addr) { return; }
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let subtract_lit = function(lit) { return; }
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let subtract_addr = function(addr) { return; }
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let hop_lit = function(lit) { return; }
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let hop_addr = function(addr) { return; }
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let jump_lit = function(lit) { return; }
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let jump_addr = function(addr) { return; }
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let carry_toggle = function() { return; }
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let carry_hop = function() { return; }
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// TEST
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let halt_and_catch_fire = [
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[0, 0],
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[1, 0],
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];
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let basic_test = [
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[3, 8], // LDA lit
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[1, 5], // STO lit
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[4, 5], // LDA addr
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[2, 6], // STO addr
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[0, 0], // END
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];
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let comp = new CPU(basic_test);
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comp.run_program();
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