When errors arise in a computing system that has plural modules, this invention corrects those errors. In the first instance, the invention excludes the computing system itself, but receives error messages from the plural modules of that system—along plural receiving connections, respectively. Plural sending connections return corrective responses to plural modules of that system, respectively. In a second instance, the invention further incorporates that system. The invention is hierarchical: plural levels or tiers of apparatus and function are present—a first (typically uppermost) one directly serving that system as described above, and others (lower) that analogously serve the first tier of the invention—and then also the subsequent tiers, in a cascading or nested fashion, down to preferably a bottom-level tier supporting all the upper ones. Each level preferably controls power interruption and restoration to higher levels. Ideally the hierarchy is in the form of a “system on chip”.