MOS6502

Mos 6502 emulator in C++.

Overview

• Jump table based
• All legal opcodes implemented and tested
  • Decimal mode not implemented yet
• All addressing modes

Project structure

• ./src/cpu/*: Main files
• ./src/memory/*: Memory utility functions used for debugging (loading, hex dump, write, read...)
• ./src/test/*: Test suite

Getting started

The MOS6502 class exposes the following functions:

• MOS6502(fWrite w, fRead r): The class constructor takes as arguments two function objects, namely std::function<void(uint16_t, uint8_t)> (for write operations) and std::function<uint8_t(uint16_t)> (for read operations). These functions are used by the MOS6502 object to access memory (or virtual memory-mapped devices), see below for an example
• void IRQ(): Generates a maskable interrupt
• void NMI(): Generates a non-maskable interrupt
• void execute(uint16_t init_PC, uint16_t end_PC): Executes code in the address range [init_PC, end_PC] (endpoints included)
• void reset(): Processor reset
• std::string info(): Returns a string containing information about the processor (Registers, Status Register, Number of cycles)
• void setBreakpoint(uint16_t addr): Set a breakpoint at the specified address (At the moment breakpoints can only be specified for addresses related to memory locations containing an opcode)
• uint8_t/uint16_t get*(): getters
• void set*(uint8_t/uint16_t): setters

Clock emulation

To disable clock speed emulation use the -D _NO_DELAY_ option during the compilation step

Example

#include <iostream>
#include "MOS6502.h"

#define SIZE 0x10000

uint8_t memory[SIZE] = {0};

void memoryWrite(uint16_t addr, uint8_t data) {
    memory[addr] = data;
}

uint8_t memoryRead(uint16_t addr) {
    return memory[addr];
}

int main(void) {

    MOS6502 cpu = MOS6502(memoryWrite, memoryRead);

    // ...
    // load program into memory
    // ...

    uint16_t startAddr = // Set start address
    uint16_t endAddr   = // Set end address
    cpu.execute(startAddr, endAddr);

    return 0;
}

Resources

• https://www.masswerk.at/6502/6502_instruction_set.html
• http://6502.org/
• https://github.com/Klaus2m5/6502_65C02_functional_tests