Editing Subsumption architecture (section)

==Layers and augmented finite-state machines==
Each layer is made up by a set of processors that are augmented [[finite-state machine]]s (AFSM), the augmentation being added [[instance variable]]s to hold programmable data-structures.  A layer is a [[Modular programming|module]] and is responsible for a single behavioral goal, such as "wander around."  There is no central control within or between these behavioral modules.  All AFSMs continuously and asynchronously receive input from the relevant sensors and send output to actuators (or other AFSMs).  Input signals that are not read by the time a new one is delivered end up getting discarded.  These discarded signals are common, and is useful for performance because it allows the system to work in real time by dealing with the most immediate information.

Because there is no central control, AFSMs communicate with each other via inhibition and suppression signals.  Inhibition signals block signals from reaching actuators or AFSMs, and suppression signals blocks or replaces the inputs to layers or their AFSMs. This system of AFSM communication is how higher layers subsume lower ones (see figure 1), as well as how the architecture deals with priority and [[action selection]] arbitration in general.<ref name="Brooks 1999"/>{{rp|12–16}}

[[File:Subsumption Architecture Abstract Diagram.png|thumb|Figure 1: Abstract representation of subsumption architecture, with the higher level layers subsuming the roles of lower level layers when the sensory information determines it.<ref name="Brooks 1999"/>{{rp|11}}]]

The development of layers follows an intuitive progression.  First, the lowest layer is created, tested, and debugged.  Once that lowest level is running, one creates and attaches the second layer with the proper suppression and inhibition connections to the first layer.  After testing and debugging the combined behavior, this process can be repeated for (theoretically) any number of behavioral modules.<ref name="Brooks 1999"/>{{rp|16–20}}