atrex66/picoc64plus

picoc64plus is a minimal Commodore 64 emulator that runs on a Raspberry Pi Pico or Pico 2 microcontroller. Rather than reproducing the full C64 hardware experience, it takes a specific angle: it runs the original C64 BASIC interpreter and Kernal ROM on the Pico, then adds new BASIC commands that let you control the Pico's own hardware pins directly from BASIC code. The 6502 processor (the CPU used by the Commodore 64) is emulated in software, running at around 3.8 to 4 million operations per second on a Pico 2. The emulator does not simulate the C64's graphics or sound chips, so it is not for playing C64 games. Instead, it is aimed at people who want to write hardware control programs using the 1980s-era BASIC language syntax. The BASIC extension adds commands for controlling the Pico's GPIO pins (PINMODE, PINOUT, PINGET), generating PWM signals (PWMSEL, PWMLVL, PWMON), communicating with I2C devices like sensors and displays (I2CADR, I2CWRT, I2CRDT), and running DMA memory transfers (DMACPY). The same hardware is also accessible through PEEK and POKE commands, which read and write memory addresses, for users writing machine code programs. You interact with the emulator over a USB serial connection using a terminal program like PuTTY on a PC. The Pico shows up as a serial device, and you type BASIC commands directly into it. Pre-compiled firmware files (.uf2) are available on the GitHub releases page for both Pico and Pico 2. To install, hold the BOOTSEL button and drag the file onto the Pico, or use the picotool command. Building from source requires the Raspberry Pi Pico SDK, CMake, an ARM GCC toolchain, and a copy of the C64 ROM files (not included for legal reasons). The project is written in C and does not list a license explicitly.