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

11.5 Extended Specification Modelling 373
purchased real-time operating system for the chosen processor. There is a wide variety
available. Some are rather standard products others are intended as a framework that
allows user defined configuration. Van Felius [vF96] explored the mapping from POOSL
to pseudo concurrent implementations in C++, using the IEEE standard 1003.1 (POSIX)
as interface to a thread library.
Hardware implementation technology decisions can lead to the exploration of various
specific functions. For instance a power-up reset may require a specific order in which
various processes or modules are activated. Programmable logic requires configuration.
Programmable logic modules can realise system parts that can be used in a flexible way.
This requires programming control that can be even remote. Saving power can require
a considered control of the activation of subsystems.
The choice of a communication technology has in general a big impact on a model.
Therefore selections should be made on the system level and as early as possible. The
world of communication technology and protocols is a rapidly growing. Depending on
the sort of system to be developed we have to cope with design according to various
standards. There is a huge amount of knowledge in the area of standards. A wide variety
of communication processors that implement particular protocols for networks or busses
is available in hardware and/or software. In depth specific knowledge is necessary when
the implementation of one or more protocols is needed. Further description is beyond
the scope of this thesis.
Selection of interface technology on the system boundary is in general postponed to
the extended modelling phase. Therefore the modelling of objects around the system
boundary needs special attention. Dedicated objects can be added to model the concrete
communication between actors and sensors that are chosen to implementation terminators.
Another example of a modelling activity in this phase is the detailed design of user
interfaces. The essential model will specify a rather abstract user interface. A command
by a user can be modelled as one single message. In reality many interactions can be
needed accompanied by checking of the interactions to give such a command. Extended
modelling refines such a user interface. User interface and interface technology affect
also an environment model developed for simulation. So refinement of this model is
also part of the activities.
11.5.5 Extended Instance Structure Diagrams
The activities in the Instance Structure Models in the extended phase are of the same
sort. Formalisation of properties by boundaries is further extended and refined based in
implementation and design decisions. Abstraction boundaries, implementation boundaries,
concurrency boundaries, and distribution boundaries annotated on a hierarchy
of clusters structure the model. Behaviour preserving transformations can be used to
improve the structure of the model and to map various processes on various implementation
modules.