CAD.4:1 - Problem frame

Use this when several control architectures appear feasible, or a change of model, hardware, rate or operating demand can invalidate an existing arrangement. Tuning each controller independently does not decide which complete arrangement should be built.

Start with the same required behavior and resource boundary for every candidate. The first useful result is a feasible whole configuration, its comparison with serious alternatives, and the conditions under which its implementation and later use remain justified.

For a fixed, qualified architecture requiring only a local parameter adjustment, use the relevant controller-design method directly and reopen the whole only if that adjustment changes a relied-on interface, resource or constraint.