Big project: splitting

The base automation does not fit on one chip. 128 lines, 4096 characters and 128 instructions per tick are enough for one subsystem, not for five. So it gets split up. The only question is: how?

Distributing tasks#

The workshop splits by responsibility, not by lines:

Every sub-chip only controls its devices. The central unit never switches a heater itself, it asks life support to do it. If the central unit fails, the subsystems keep running. If a subsystem fails, the central unit notices and reports it.

Interfaces#

Between the chips only defined values flow over defined paths – Logic Memories or the setting of a housing. For every interface: one writer, clear meaning, clear value range. A sub-chip that does not understand a request does the safe thing and reports what it understood.

Several small values fit into one single status word, just as in bit week:

move status sup                  # bit 0: supply
ins status exh 1 1               # bit 1: exhaust
ins status fault 2 1           # bit 2: sensor fault
mul tmp flush 2
add tmp tmp normal
ins status tmp 4 2           # bits 4-5: understood request

Register and memory plan#

Every chip has a plan of which register holds what, and every interface a note of who writes it. In the code the register plan is the alias block, the memory plan is in the header comment. Whoever changes a chip later sees straight away what he must not touch.