perfect6502

perfect6502 is a MOS 6502 CPU emulator that performs a simulation of the original NMOS 6502 netlist that was extracted by the visual6502.org project.

Consequently, perfect6502 is

• perfect: It is not a reimplementation of the 6502, but a simulation of the original transistors. Its complete behavior, its internal state and its outputs are half-cycle exact.
• slow: Even though perfect6502 is highly optimized C code, it achieves only 1/30 of the speed of a 1 MHz 6502 on a high-end CPU of 2025.

perfect6502 is useful for

• understanding and reverse engineering the 6502
• debugging 6502 emulators by running them side by side with perfect6502

Usage

As a demonstration and as a performance/regression test, perfect6502 is hooked up to Commodore BASIC (cbmbasic).

You can compile the project with

$ make

and run it with

$ cbmbasic/cbmbasic

You should get the following output:

	**** COMMODORE 64 BASIC V2 ****

 64K RAM SYSTEM  38911 BASIC BYTES FREE

READY.

Benchmarking

You can measure the performance of the emulator by running make benchmark. It will print the number of half-cycles, the elapsed time, and the speed in half-cycles per second. On a 1 MHz 6502, reaching the READY. prompt takes 33155 half-cycles (0.017 sec).

Credits

perfect6502 is is written by Michael Steil and derived from the JavaScript visual6502 implementation by Greg James, Brian Silverman and Barry Silverman.

Contributing

Further performance optimizations are gladly accepted.