Embedded Programming B. Furman 09MAY2011

Learning Objectives Distinguish between procedural programming and embedded programming Explain the Events and Services embedded programming framework  Explain what an Event is  Explain what a Service is Explain the key rule and its two corollaries Describe how an event checking routine works for  Discrete quantities  Analog quantities Develop code for:  an event checking routine  a service  an event driven system

Mechatronics Concept Map Controller (Hardware & Software) System to Control Sensor Signal Conditioning Power Interface Actuator User Interface Power Source BJ Furman 22JAN11 ME 106 ME 154 ME 157 ME 195 ME 120 ME 297A ME 106 ME 120 ME 106 ME 190 ME 187 ME 110 ME 136 ME 154 ME 157 ME 182 ME 189 ME 195 ME 106 ME 120 ME 106 INTEGRATION

Procedural vs. Embedded Programming Procedural  ME 30/CmpE 46  Computation and analysis programs  Mostly sequential Start  …  End  Known inputs and outputs Program is in control  Predictable operation and timing Embedded  ME 106  Inputs and outputs can occur at any time, in any order and are not predictable  Inputs can come from multiple sources Sensors, user inputs, or internal (timer, ADC, etc.)  May handle simultaneous inputs and outputs  Program never ends

Event Driven Program Structure Programming task divides into:  Checking for events  Servicing events when they occur Event  A detectable change or transition in something of interest Button press (before: not pressed, after: pressed) ADC complete flag bit set Service  An action taken in response to an event

Requirements for Events and Services The occurrence of events must be checked for continuously and often Services must execute quickly and must be non-blocking  Ex. Determine if a switch has closed Blocking code:  while(digitalRead(pin) == HIGH);

Event Checkers for Discrete Events Ex. Check that a switch has closed  Pseudocode IF switch is closed AND switch was open last time, THEN  SwitchClosed event has occurred ELSE  SwitchClosed event has not occurred  Need to keep track of the state of the switch (i.e., maintain its history) Use a state variable Will need to be declared as a static local variable in the function that checks for the event  Need to retain the value between successive calls to the event checking function

Code to Check for Discrete Events

Events involving an analog quantity A single-valued threshold will likely result in “chatter” when the quantify of interest is near the threshold

Event Checkers for Events Involving Analog Quantities Filtering the signal may help Add hysteresis in the event checker  Make the criteria for when the event occurs a variable instead of a fixed value Initially threshold is set to an upper value As soon as the signal crosses the threshold, the threshold is dropped to a lower value  Pseudocode: Set threshold to high value IF var is greater than or equal to the threshold, THEN  Event has happened  Set threshold to lower value ELSE  Event has not happened

Event Detection with Hysteresis

Code to Check for Events With Analog Quantities

Main body of Events & Services Code