buzai / perfect6502

perfect6502, a MOS 6502 CPU emulator that performs a simulation of the original NMOS 6502 netlist

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, achieves only 1/30 of the speed of a 1 MHz 6502 on a high-end CPU of 2020.

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 use the UNIX time tool to measure the performance of the emulator. Run time cbmbasic/cbmbasic and press Ctrl+C once it has reached READY. – the "user" time is the effective time that was required to reach character input. On a 1 MHz 6502, this takes 0.05 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.