Almost half a century after it was first launched, the Commodore PET isn’t going to impress anybody with its processing velocity. Its 6502 processor stacked up effectively towards the competitors again within the day, however that day has lengthy since handed. These days these computer systems are utilized by fans who wish to relive the expertise of taking part in a PETSCII sport or typing in a BASIC program from {a magazine}, however they’ve little sensible worth.
Even so, Ted Fried has a Commodore PET 4016 and needs to see simply how far it may be pushed. This can be a sport with out guidelines, so Fried had no qualms about swapping out the unique processor for an MCL65+ 6502 CPU drop-in substitute board first. This board makes use of a Teensy 4.1 growth board with an Arm Cortex-M7 processor and 1MB of reminiscence, so it will probably do much more than simply faithfully replicate the performance of an actual 6502.
Nonetheless, merely ramping up the clock velocity of the processor isn’t going to hurry up a PET — at the very least not a lot. Different system elements, particularly RAM and ROM, have strict limits to how briskly they will function earlier than timing constraints are violated and undefined behaviors begin to break actually the whole lot. The MCL65+ can get round at the very least a few of this by additionally emulating system RAM and ROM with its onboard reminiscence that’s far sooner.
That is achieved by way of three acceleration modes: Mode-1, Mode-2, and Mode-3. Mode-1 completely replicates a inventory 6502 with cycle-accurate reads and writes. Mode-2 accelerates reads, whereas Mode-3 accelerates each reads and writes by solely utilizing the Teensy’s personal reminiscence, permitting it to run at as much as 900MHz, which is 900 instances sooner than a standard PET.
Fried demonstrated all of those modes by working quite a lot of video games and BASIC applications below every. For sure, the accelerated modes ran issues far sooner than an unmodified PET ever may. This simply is likely to be the world’s quickest Commodore PET ever to exist!A Commodore PET 4016 accelerated by an MCL65+ (📷: Ted Fried)
The substitute processor (📷: Ted Fried)
