Classic computing fanatic Ted Fried has launched one other Teensy 4.1-powered drop-in alternative for a basic computing chip, this time turning his focus to the Motorola 68000 and its native bus interface.

“The MCL68+ is a Motorola 68000 drop-in alternative emulator. It makes use of the Teensy 4.1 to emulate each the microprocessor and the native bus interface at full pace,” Fried explains of his newest creation. “It’s the most bold drop-in emulator I’ve designed up to now, and I’m happy with the progress I used to be in a position to obtain.”

One among Fried’s hobbies is to make use of comparatively high-performance however low-cost microcontroller boards to create drop-in replacements for processors from basic computer systems, generally to work round shortages of authentic parts however typically to crank up the pace and enhance efficiency or add lacking options. Earlier initiatives have included the MCL64 improve chip for the Commodore 64, the MCL86jr for the IBM PCjr, and the MCL65+ — uncommon for having truly “downgraded” an Apple II into an Apple I suitable.

This time, Fried targeted on the Motorola 68000 — a component greatest identified for driving Apple’s Macintosh household of computer systems in addition to Commodore’s Amiga vary. Given the complexity of the half, it proved a problem — leading to an emulation which Fried says is “the quickest bit-banged native bus pace that I’ve ever achieved” on the full 7.8MHz of the unique {hardware}.

“It required a lot of tips resembling pre-calculating addresses and utilizing arrays to map GPIO [General-Purpose Input/Output] values to the Teensy’s output registers,” Fried explains. “The Motorola 68000 additionally required extra pins than had been out there on the Teensy 4.1, so I used a collection of byte-wide latches to shift out the handle and information busses. I additionally wanted to multiplex just a few different indicators to squeeze all of it onto the Teensy’s pins.”

The {hardware} aspect of the undertaking is already full, however there are just a few kinks to iron out within the emulator working atop it. “The progress all the time stops right here,” Fried says of a video exhibiting an MCL68+ booting an Apple Macintosh 512k part-way into the working system, “however I’m able to transfer the cursor round with the mouse and reboot the machine, so the system is just not locked up. I traced the error to an tried subroutine soar to a misaligned handle, however I’ve not had the time to hint the code backwards to seek out the place this handle comes from.”

Extra particulars on the MCL68+ can be found on the Microcore Labs weblog; the undertaking supply code and {hardware} design recordsdata are revealed to GitHub below an open supply license.