On the 6502 side he wrote a bootloader in assembly language, which bit-bangs the SPI protocol to communicate with the wireless module. A simple user interface is included to allow the user to ...

There’s also a tiny PCB-mount speaker, as well as I2C, SPI, and UART interfaces. Finally, there’s 2 MB of flash onboard, and a 40-pin connector hosting all the 6502 signals that you know and love.