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

384 Case Study
Feeding Unit Image. On the reception of a feed message, the Feeding Unit adds a new
item to the mailing product. The unit can detect the occurrence of an incorrectly fed
item (misFed) as well as the erroneous situation that more than one copy of the item was
fed (doubleFed). It is further possible to detect whether the Feeding Unit is mounted to
the station or not by a continuous status message (mounted,notMounted).
Before any item is actually being fed, the Service Scheduler investigates the services
offered by the feeder station. For this purpose it requests the status of the
Feeding Unit Image. The image answers whether a Feeding Unit is mounted, and if
so what Service it offers 8 .
Upon reception of the schedule message, the Service Scheduler asks the appropriate
Product Info Keeper for each offered service 9 whether this service is required. In case the
feeding service is required, the Service Scheduler commands the Feeding Unit Image to
perform the feed action for the appropriate mailing product. Based on the Initial Position,
the Feeding Unit Image can calculate at what position the feed action actually has to take
place. Subsequently the Feeding Unit Image requests the Transporter Image to get woken
at this position. If it receives the wakeUp message, the Feeding Unit Image triggers the
Feeding Unit and monitors if the feed action is carried out properly. After successful
completion of the feed action, the Service Administrator is informed and this administrator
updates the appropriate product Info Keeper. The situation that the feed action is not
completed successfully is not covered in this scenario.
12.3.5 Other Scenarios and Other Stations
The Product Flow Scenario and Feeding Scenario only address a (simplified) part of
the necessary behaviour. Together the scenarios describe a number of essential objects
and flows to perform the normal course of behaviour of a production line. But even
for this purpose the scenarios are not complete. To achieve completeness and to study
and specify other forms of behaviour, other scenarios had to be elaborated. Examples
of important scenarios are:
Batch job preparation scenario.
Initialisation and configuration scenario.
Error handling scenario.
Maintenance, repair and test scenario.
Product information distribution scenario.
Failure effect analysis scenario.
8 The service can for instance be the feeding of a floppy disk or of a certain magazine.
9 In case of the feeder station, at most one service can be offered. In general, a station can perform
many services.