Two Stop Bits

6o6 v1.1 is a performance update to a 6502-on-6502 virtualization library written in 6502 assembly. Key improvements include a fast path for zero page stores (in addition to loads), trimmed instruction dispatch overhead, and better IRQ/BRK handling. Benchmarks show a 2.6% reduction in host instructions needed to pass Klaus Dormann's 6502 validation suite, dropping from 52.3 to 51.0 host instructions per guest instruction. To celebrate Apple's 50th anniversary, the author built VA1, an Apple-1 emulator running on a Commodore 64 or Apple II using 6o6. The post also surveys the history of Apple-1 emulators on 8-bit hardware, covering implementations for the Apple II, SAM Coupé, and Commodore 64, comparing their accuracy and trade-offs. Future plans include fast paths for stack operations and a dynamic page table system.

Old Vintage Computing Research: 6o6 v1.1: Faster 6502-on-6502 virtualization for a C64/Apple II Apple-1 emulator