There is no CPU that is better understood than the 6502 and its cousins the 6510, 6507, 6509, and whatever we’re calling the CPU in the NES. With this vast amount of documentation, just about anything can be done. Want a discrete and un-discreet 6502? Sure thing. It’s the NMOS version, though. Want an emulated version. Sure. With libraries porting the 6502 to every platform ever, there’s only one place left to go: putting a 6502 in a Commodore 64. Make it dual-core, too, so we can run CP/M.
This build is based on one of [telmomoya]’s earlier builds – a soft-core 6510 running on an ARM Cortex M3. The inspiration for this build came from a 6502 emulator running on an Arduino, which got [telmomoya] wondering what would happen if he attached some external RAM, CIA or a SID. Doing this on an Arduino is hard, but there are a few 5 Volt tolerant ARM chips out there, and with a few banks of SRAM, [tel] quickly had an emulated 6502 running EhBasic.
Running an emulated 6502 on an ARM chip is nothing new. What makes this build spectacular is the adaptation to the C64 motherboard. Since [telmomoya] was already breaking out the data and address lines to go to the SRAMs, it didn’t take much extra work to simply build an adapter for the DIP40 CPU socket on a C64. A few 74-series logic chips made the interface easy, and after a bit of soldering, [telmomoya] had a Commodore 64 powered by an ARM chip.
If you’re emulating one chip, you can emulate two, and with the Commodore 64, this leads to a few interesting possibilities. The C64 had a CP/M cartridge — a cartridge that contained a Z80 CPU, sharing the data and address bus with the 6510. This cartridge allowed the ‘toy computer’ C64 to run the ‘business’ CP/M operating system (and the Z80 made the Commodore 128 much cooler). Since [telmomoya] was already emulating a CPU, emulating a second CPU wasn’t really that hard.
It’s a phenomenal build, and great if you’ve ever wanted to speed up VisiCalc.