Ted Fried Units His Sights on the Apple Macintosh with the Teensy 4.1-Based mostly MCL68+ Processor Emulator

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

“The MCL68+ is a Motorola 68000 drop-in substitute 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 formidable drop-in emulator I’ve designed thus far, and I’m happy with the progress I used to be capable of obtain.”

Ted Fried’s newest Teensy-emulated traditional pc chip is the Motorola 68000, within the type of the MCL68+. (📹: Ted Fried)

One in all Fried’s hobbies is to make use of comparatively high-performance however low-cost microcontroller boards to create drop-in replacements for processors from traditional computer systems, generally to work round shortages of unique parts however usually to crank up the pace and increase 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 really “downgraded” an Apple II into an Apple I appropriate.

This time, Fried centered on the Motorola 68000 — an element finest recognized 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 comparable to 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 sequence of byte-wide latches to shift out the deal with and knowledge busses. I additionally wanted to multiplex a number of different indicators to squeeze all of it onto the Teensy’s pins.”

The {hardware} aspect of the venture is already full, however there are a number of kinks to iron out within the emulator working atop it. “The progress all the time stops right here,” Fried says of a video displaying 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 bounce to a misaligned deal with, however I’ve not had the time to hint the code backwards to seek out the place this deal with comes from.”

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

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