Editing Guarded Command Language (section)

=== Asynchronous circuits ===

Guarded commands are suitable for [[quasi-delay-insensitive circuit]] design because the repetition
allows arbitrary relative delays for the selection of different commands. In this application,
a logic gate driving a node ''y'' in the circuit consists of two guarded commands, as follows:

 PullDownGuard → y := 0
 PullUpGuard → y := 1

''PullDownGuard'' and ''PullUpGuard'' here are functions of the logic gate's inputs,
which describe when the gate pulls the output down or up, respectively. Unlike classical
circuit evaluation models, the repetition for a set of guarded commands (corresponding to an asynchronous circuit) can accurately describe all possible dynamic behaviors of that circuit.
Depending on the model one is willing to live with for the electrical circuit elements,
additional restrictions on the guarded commands may be necessary for a guarded-command description
to be entirely satisfactory. Common restrictions include stability, non-interference, and absence
of self-invalidating commands.<ref name="synthesis_tr">{{cite web | title=Synthesis of Asynchronous VLSI Circuits|last=Martin | first=WILLIAM | url=http://resolver.caltech.edu/CaltechCSTR:1991.cs-tr-93-28 }}</ref> AI