WatchDog System

1 Event Generator Model

connector eventPort discrete Boolean signal; end eventPort;
model EventGenerator parameter Real eventTime = 1; eventPort dOutput; equation dOutput.signal = time > eventTime; end EventGenerator;
connector EventPortInput = input Boolean;
connector EventPortOutput = output Boolean;
model EventGenerator parameter Real eventTime=1; EventPortOutput dOutput; equation dOutput = time>eventTime; end EventGenerator;

2 WatchDog 1

The watchdog system shown in Figure 1 consists of the watchdog itself and three event generators, emitting On events, Off events and deadlineSignal events.

WatchDog System

A Modelica model of the watchdog system follows below, consisting of the watchdog itself and the three event generators. The watchdog is formulated using an algorithm section since otherwise the multiple when-equations would cause multiple assignments to be reported for the variable watchdogActive.

This version of the WatchDog receives three events: two commands to switch the watchdog on and off, and a "deadline" event. The watchdog must emit an "alarm" whenewer the deadline occurs when the watchdog is on. Initially it is turned of.
This is the algorithmic implementation.

model WatchDogSystem EventGenerator turnOff(eventTime=0.25); EventGenerator turnOn(eventTime=1); EventGenerator deadlineEmitter(eventTime=1.5); WatchDog watchdog; equation connect(turnOn.dOutput, watchdog.dOn); connect(turnOff.dOutput, watchdog.dOff); connect(deadlineEmitter.dOutput, watchdog.dDeadline); end WatchDogSystem;
model WatchDog EventPortInput dOn; EventPortInput dOff; EventPortInput dDeadline; EventPortOutput dAlarm; Boolean watchdogActive(start=false); // Initially turned off algorithm when dOn then // Event watchdog on watchdogActive := true; end when; when dOff then // Event watchdog off watchdogActive := false; dAlarm := false; end when; when dDeadline and watchdogActive then // Event Alarm! dAlarm := true; end when; end WatchDog;

3 Simulation of WatchDogSystem

simulate( WatchDogSystem, stopTime=2 )
plot( watchdog.dAlarm)

4 WatchDog 2

This version of the WatchDog receives three events: two commands to switch the watchdog on and off, and a "deadline" event. The watchdog must emit an "alarm" whenewer the deadline occurs when the watchdog is on. Initially it is turned off. This is the equation-based inplementation of the watchdog1.

model WatchDog2 EventPortInput dOn; EventPortInput dOff; EventPortInput dDeadline; EventPortOutput dAlarm; Real internalTime1(fixed=true), internalTime2(fixed=true); equation when change(dOn)then internalTime1 = time; end when; when change(dOff)then internalTime2 = time; end when; when change(dDeadline) and time>internalTime1 and internalTime1>internalTime2 then dAlarm=true; end when; end WatchDog2;
model WatchDogSystem2 EventGenerator turnOn(eventTime=1); EventGenerator turnOff(eventTime=0.25); EventGenerator deadlineEmitter(eventTime=1.5); WatchDog2 watchdog; equation connect(turnOn.dOutput,watchdog.dOn); connect(turnOff.dOutput,watchdog.dOff); connect(deadlineEmitter.dOutput, watchdog.dDeadline); end WatchDogSystem2;

5 Simulation of WatchDogSystem2

simulate( WatchDogSystem2, stopTime=4 )
plot( watchdog.dAlarm)

6 WatchDog Clocked

A clocked version of the model called WatchDogSystemClocked, is shown below. The main difference is that a global clocked timer variable has been introduced, and that the event generator detects when to emit a clocked signal synchronized with the clock ticks of the global clock by the equation dOutput = timecmp==true and previous(timecmp)==false. An if-then-else statement is used instead of the when-statements in the unclocked version since clocked when-statements are currently not available in the Modelica language.

model WatchDogClocked "Version with equation section, if-then-else" EventPortInput dOn; EventPortInput dOff; EventPortInput dDeadline; EventPortOutput dAlarm(signal(start=false)); Boolean watchdogActive(start=false); // Initially turned off equation if dOn then // Event watchdog on watchdogActive =true; dAlarm = previous(dAlarm); elseif dOff then // Event watchdog off watchdogActive =false; dAlarm =false; elseif dDeadline and previous(watchdogActive) then //Event Alarm! watchdogActive = previous(watchdogActive); dAlarm =true; else watchdogActive = previous(watchdogActive); dAlarm = previous(dAlarm); end if; end WatchDogClocked;

This model contains clocked synchronous constructs that are not yet fully supported by OpenModelica as of October 2015, but may start working within the near future.Hence the Simulation of this models does not work

setCommandLineOptions("+std=3.3")
simulate(WatchDogClocked)