Chapter 13 — A Cooperative Runtime

This chapter will bring the hardware pieces together.

Planned coverage:

the no-background-task constraint
a main loop shaped as scan service plus logic service
keeping the matrix visible while doing useful work
servicing sound and seven-segment scan during the same loop
polling keypad input without blocking scanout
spreading a logical frame across several passes
deciding what belongs in shared hardware routines and what belongs in program logic

The key pattern is:

main_loop:
    call scan_tick
    call logic_tick
    jr main_loop

The real work is deciding what each tick is allowed to do before the hardware needs service again.