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

12.3 The Essential Specification 395
monitorTransporter
interrupt
( titr?productArrived;piti!productArrived
or piti!currentPosition(position asInitialPosition)
or wake?wakeAt(aPosition,anId);wakeupQueue schedule(aPosition,anId)
or poti?stop;speed setToZero;titre!move(speed)
or poti?start;speed setToMaximum;titre!move(speed)
)
The initialise method starts by initialising the instance variables position, pendingWakeups
and speed. Then it sends the message move(speed) to the Transporter (see also Figure 12.6)
and starts its normal course of behaviour. This normal course of behaviour consists of
the monitoring of the Transporter. The behaviour is modelled by the monitorTransporter
method. This method can be interrupted at any time by the arrival of either the productArrived,
wakeAt, stop or start messages. It can further be interrupted always when
the Product Input Handler reads the current position. In this way the current position is
continuously available. The monitorTransporter method is defined as:
monitorTransporter
titr?encoderPulse;
position increment;
if pendingWakeups firstPosition = position then wakeupPendings fi;
monitorTransporter
The method repeatedly accepts encoderPulses. For each encoderPulse, the position is
increased by one. At each position, it is checked whether there are pending processes
that need to be woken up at this position. If this is so, the method wakeupPendings is
invoked. This method is specified by:
wakeupPendings idSet:Set anId:Id
idSet:=wakeupQueue idSetAtFirstPosition;
do (idSet isEmpty not) then
anId:=idSet pickElement;
wake!wakeup(anId)
od
This method first retrieves and removes the collection of process identifiers at the current
position. The pickElement message is used to select and remove an arbitrary element
from the idSet. For each identifier anId in this set, the corresponding process is woken
up through the wakeup(anId) message.
Now that we have specified a number of process classes, we show two specifications
of data classes. The first data class we will explain is PI. The first part of the class
description is as follows: