Specification of Reactive Hardware/Software Systems - Electronic ...

394 Case Study
process class
Transporter Image
instance variables
position
speed
pendingWakeups
: Position
: Speed
: WakeupQueue
As indicated by the relations in the Object Class Diagram of Figure 12.9, a
Transporter Image controls the Speed of the Transporter and keeps track of the Position of
the transport mechanism. Based on the position information a Transporter Image can
wake up processes at requested Positions. To store the identifiers of the objects that are
pending to be woken up, the instance variable pendingWakeups of type WakeupQueue is
used. A WakeupQueue is a data object that stores for each wakeup Position a collection
of object identifiers. The data class WakeupQueue is not further elaborated.
The next part of the specification of process class Transporter Image directly follows from
Figures 12.8 and 12.6:
communication channels
piti wake titr poti
message interface
piti!productArrived
piti!currentPosition(InitialPosition)
wake?wakeAt(Position,Id)
wake!wakeup(Id)
titr?productArrived
titr!move(Speed)
titr?encoderPulse
poti?stop
poti!start
The Transporter Image class is a class with rather complex behaviour. This is due to the
diverse incoming interrupt flows and an outgoing continuous flow (see Figure 12.6). It
will appear, however, that this complex behaviour is easily and elegantly expressible
in POOSL. The behaviour of a Transporter Image starts with a piece of initialisation
behaviour expressed in terms of method initialise:
initial method call
initialise
instance methods
initialise aPosition:Position anId:Id
position:=new(Position) setToZero;
pendingWakeups:=new(WakeupQueue) makeEmpty;
speed:=new(Speed) setToMaximum;
titre!move(speed);