We love Ted Fried  drop-in CPU replacements for retro systems. MCL65-Fast is a little different, however, in that rather than simply emulating the Apple II’s 6502 CPU.  Arduino code runs directly on Teensy 4.1 at 800MHz+, with access to all of the device’s peripherals and slots.

In order to interact with the Apple’s video and keyboard, Ted implemented custom printf(), and scanf() functions, effectively abstracting away the legacy hardware to work like “normal” C. In the video below, a demonstration of a countdown program is shown first in cycle-accurate mode, taking around ten seconds, and then running directly on the Teensy, outputting the sequence to the Apple II’s display almost instantly. What would you do with an 800MHz Apple II? Check out the source on GitHub and find out more about the project on Ted’s blog.