Notes

The 🌀 key is called the Koru key.

To reset the machine hold down Escape-Alternate-Koru.

F0 performs a non-maskable interrupt. To register the key, set the NMIADD system variable to call this routine:

;   // F0 pressed
usrnmi:
    ld a, $ff;        // use a byte to set key state (0 is off)
    ld $<addr>, a;    // write state to arbitrary address
    reti;             // return from interrupt