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

174 Modelling of Concurrent Reactive Behaviour
message
a) throw away new message arriving at full buffer
message
b) throw away oldest message from full buffer
Figure 6.9: Buffered Message Flow with Discard
guard emergency process B
Figure 6.10: An Interrupt Flow
flow, must realise the continuous readiness to accept an interrupt. Without special
interrupt language primitives, a behaviour description would become very disordered.
This is because the modelling of an interrupt then would mean that we had to define
the alternative behaviour to accept the interrupt for any statement. (Section 9.6 gives an
elaborate description of this problem). We solve this problem by offering two language
primitives:
the abort statement;
the interrupt statement.
An interrupt statement specifies that a piece of behaviour can be interrupted at the
instants between the execution of the process statements, and can be resumed later, so
that the original behaviour is continued from the place where it was interrupted.
An abort statement specifies that a piece of behaviour can be stopped at the instants
between the execution of the process statements, that form this piece of behaviour.
Alternative behaviour that must be performed after the abort can be specified.
The graphical symbol does not specify whether an interrupt message flow must be
interpreted as an abort or as an interrupt. The final decision for an abort or an interrupt
is made during the creation of the unified POOSL description. It can also be described
in a scenario description (see also Section 6.5).
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