breadcomp80v1

It can boot CP/M3, blink some diodes, play some tunes and talks to the Pi5 over GPIO.

This was supposed to be nothing more than a practical joke which quite unexpectedly worked out. It is not optimized (never meant to be), the CP/M3 port working on it is very crude and the bit-banging SPI over AY's I/O ports is terribly slow when it comes to accessing the SD Card adapter (C:). There are several awkwardness in the design, e.g., the first occurence of the ~HALT signal is disconnecting ROM, leaving only the RAM to be accessible by the CPU until RESET (actually, it's this feature that made CP/M bootable on it!). Of the 128kB of available RAM, only 96kB can be used, the upper 32kB is always the same (CP/M's BDOS and BIOS are there), the lower 32kB can be banked on and off by the CP/M BIOS. It is being used for the 12kB ramdisk(A:) and for storing the copy of the CCP (CP/M's shell) so it does not need to be loaded from the SD Card.

It was more fun than you all think.