m65xx is a simple, clean, and cycle-ticked emulator for the MOS Technology 6502 CPU.

Please note that the projects has been compiled using std=c2x, this version alongside std=c11 are the recommended versions.

Successfully compiled under MacOS Sonoma and Fedora 42. If you are using Windows, please use WSL.

This project is licensed under the GNU GPLv3, please abide by the license.

Cycle-ticked emulation — Accurate per-clock-cycle simulation of instruction timing

MOS 6502 core — Fully implements the original 6502 instruction set (both documented and undocumented instructions)

Planned 65C02 support — Adding both documented and undocumented 65c02 instructions in the future

The 6502 emulator has been tested by the following test suites:

• Klaus Dormann (6502): functional, decimal and interrupts tests
• AllSuiteASM
• Timing Test
• TomHarte 6502 test suite

To build and run:

git clone https://github.com/cdunku/m65xx.git
cd m65xx
make # For production build
make release # For release build

If you want to run a specific test file you can edit the main function:

int main(void) {
  ...
  
  // Runs all tests at once for TomHarte:
  
  printf("Starting 6502 test...\n");
  // for(int i = 0; i < 0x100; i++) {
  //  char file[50];
  //  snprintf(file, sizeof(file), "tests/6502/v1/%02x.json", i);
  //  pass += m65xx_harte_tests(&m, file);
  // }
  // printf("Tests passed = %d\n", pass);
  
  // For running a test for a specific opcode:
  // Pass: 1 (All tests pass), Pass: 0 (A test has failed)
  /*
  pass = m65xx_harte_tests(&m, "tests/6502/v1/00.json");
  printf("Pass: %d, opcode: 0x%02X\n", pass, m.ir);
  */

  // AllSuiteA test
  // allsuiteasm(&m);

  // Timing test for legal opcodes
  // m6502_timing_test(&m);

  // Klaus Dormann test
  // m6502_decimal_test(&m);
  // m6502_functional_test(&m);
  // m6502_interrupt_test(&m);

  ...
}

Additionally, adding the if(m->tcu == 0) { m6502_print(m); } statement right after the m65xx_tick(m) function in the test functions will print out information in the following format:

PC:0400 A:00 X:00 Y:00 S:FD [--1-----]| cyc=2 d8---- CLD
PC:0401 A:00 X:00 Y:00 S:FD [--1---Z-]| cyc=4 a900-- LDA #$00
PC:0403 A:00 X:00 Y:00 S:FD [--1---Z-]| cyc=8 8d0302 STA $0203
PC:0406 A:00 X:FF Y:00 S:FD [N-1-----]| cyc=10 a2ff-- LDX #$FF
PC:0408 A:00 X:FF Y:00 S:FF [N-1-----]| cyc=12 9a---- TXS
PC:0409 A:00 X:FF Y:00 S:FF [--1---Z-]| cyc=16 adfcbf LDA $BFFC
PC:040C A:00 X:FF Y:00 S:FF [--1---Z-]| cyc=18 297e-- AND #$7E
PC:040E A:00 X:FF Y:00 S:FF [--1---Z-]| cyc=22 8dfcbf STA $BFFC
PC:0411 A:00 X:FF Y:00 S:FF [--1---Z-]| cyc=26 adfcbf LDA $BFFC
PC:0414 A:00 X:FF Y:00 S:FF [--1---Z-]| cyc=28 297d-- AND #$7D
PC:0416 A:00 X:FF Y:00 S:FF [--1---Z-]| cyc=32 8dfcbf STA $BFFC
PC:0419 A:02 X:FF Y:00 S:FF [--1-----]| cyc=34 a902-- LDA #$02
PC:041B A:02 X:FF Y:00 S:FF [--1-----]| cyc=38 8d0302 STA $0203
PC:041E A:00 X:FF Y:00 S:FF [--1---Z-]| cyc=40 a900-- LDA #$00
...