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

226 Modelling of Concurrent Reactive Behaviour
Verification of the specified timing requirements can be performed statically or dynamically.
Statically means that the design is checked for timing constraints that will be
realised statically. For hard real-time constraints a static approach is relatively safe. In
software this means for instance the verification of timing constraints at compile time.
Recall that we propose to specify systems using a static channel structure for the interconnection
of processes, for early architecture design, and for a pre-defined pool of
process objects. We expect to be able to handle hard real-time constraints adequately.
We will offer the designer options to specify time critical system parts in a static way.
However we also offer more dynamic modelling with data objects for less critical system
parts.
6.7.4 First Results of Formal Description of Timing Requirements
The formal description of time requires that primitives for time description can be incorporated
in the formal semantics. Geilen [Gei96] incorporated a delay primitive in
the operation semantics of POOSL. His research was initially directed to the comparison
of existing real-time algebras and languages based on [NS92]. The properties of
various approaches are described by using concepts such as must-timing, may-timing,
synchrony, action urgency, etcetera. The integration of the primitive required special
attention for the interaction in the semantics with the or statement, the interrupt and the
guarded command. The time model of channels is currently subject of further research.
Geilen evaluated the use of the new delay primitive for expressing computation time,
time-outs, watchdogs and communication delays. We discovered various new and
rather unexpected new possibilities of the language with the new primitive. This led
to a current research towards broadcast messages and the grain of interruptability of
behaviour descriptions.
6.8 Summary
This chapter describes the concepts for the description of complex dynamic behaviour.
The subjects that are covered, complete our description of concepts.
Concurrent process objects can autonomously perform their operations at their own
speed. This makes our method suitable to describe distributed concurrent hardware/software
systems and (pseudo-) concurrent systems. Internal behaviour of process
objects is sequential. Concurrency boundaries specify the concurrency properties
of modules on system level. Interleaving semantics are used for the formal behaviour
description of concurrency.
Process objects can perform a variety of forms of communication. These forms are
sufficient to describe a wide variety of systems. POOSL offers an abort as well as
an interrupt construct to support interrupting communication. This gives the ability
for describing the interruption of concurrent (infinite) behaviour, and for modelling
hardware interrupt mechanisms. We defined a collection of message flow symbols.