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Seminar 7: Multi-State Systems and Function Sequences

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Introduction Two broad categories of multi-state systems: • Multi-State (Timed) In a multi-state (timed) system, the transition between states will depend only on the passage of time. For example, the system might begin in State A, repeatedly executing FunctionA(), for ten seconds. It might then move into State B and remain there for 5 seconds, repeatedly executing FunctionB(). It might then move back into State A, ad infinituum. A basic traffic-light control system might follow this pattern. • Multi-State (Input / Timed) This is a more common form of system, in which the transition between states (and behaviour in each state) will depend. | Seminar 7 Multi-State Systems and Function Sequences Copyright Michael J. Pont 2001-2006. Contains material from Pont M.J. 2002 Embedded C Addison-Wesley. PES I - 177 Introduction Two broad categories of multi-state systems Multi-State Timed In a multi-state timed system the transition between states will depend only on the passage of time. For example the system might begin in State A repeatedly executing FunctionA for ten seconds. It might then move into State B and remain there for 5 seconds repeatedly executing FunctionB . It might then move back into State A ad infinituum. A basic traffic-light control system might follow this pattern. Multi-State Input I Timed This is a more common form of system in which the transition between states and behaviour in each state will depend both on the passage of time and on system inputs. For example the system might only move between State A and State B if a particular input is received within X seconds of a system output being generated. The autopilot system discussed at the start of this seminar might follow this pattern as might a control system for a washing machine or an intruder alarm system. Copyright Michael J. Pont 2001-2006. Contains material from Pont M.J. 2002 Embedded C Addison-Wesley. PES I - 178 For completeness we will mention on further possibility Multi-State Input This is a comparatively rare form of system in which the transition between states and behaviour in each state depends only on the system inputs. For example the system might only move between State A and State B if a particular input is received. It will remain indefinitely in State A if this input is not received. Such systems have no concept of time and - therefore - no way of implementing timeout or similar behaviours. We will not consider such systems in this course. In this seminar we will consider how the Multi-State Time and Multi-State Input Time architectures can be implemented in C. Copyright Michael J. Pont 2001-2006. Contains .