CIS 542 Embedded Systems Programming – Summer 2013 Lecture ...

33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
}
state = disarmed;
disarm_system();
}
else {
state = alarm_sounding;
sound_alarm();
}
break;
}
break;
case alarm_sounding:
switch (signal) {
case quiet:
if (password_correct()) {
state = armed;
arm_system();
}
break;
}
break;
}
Alternatively, we could make “state = armed” the first statement in the “arm_system” function, but you
could conceivably have a situation in which a function is called in two different states, so you
shouldn't bind the state and the functionality too much.
Testing
Let's look at another example. It's the cruise control system for a car. Here's the specification:
• if the driver chooses to accelerate, the speed increases by 10, unless that would put the speed
over 100, in which case it doesn't change
• if the driver chooses to break, the speed decreases by 10; if that would put the speed below 0,
the speed becomes 0
• if the speed is 0, the car stops