Page 76 - Mechatronic Systems Modelling and Simulation with HDLs

4.2 FIELDS OF APPLICATION 65

and semantics of hardware description languages will be represented based upon
the example of the IEEE standard 1076.1 (VHDL-AMS) passed in March 1999.
This lays the foundation for the subsequent chapter on modelling.

4.2 Fields of Application

4.2.1 Formulation of specification and design

A formalised circuit description on a behavioural level, such as that provided by a
hardware description language, represents the precise specification and documen-
tation of a circuit. In many cases informal paper specifications are associated with
problems, for example, if certain operating states are not predicted and are thus
not specified. These difficulties are avoided by using a formal, programme-like
specification. With such a specification it is generally immediately clear if a sys-
tem is incompletely or even contradictorily specified. Furthermore, the hardware
description language is available for reference in all cases of dispute. In such a
case a simulation should be capable of clearing up all doubt. Furthermore, this
route automatically provides an entry into a universal design sequence. On the
basis of abstract descriptions, increasingly detailed representations are developed
or generated, descriptions which can be verified against one another. In this man-
ner both the actual design problem and the problem of consistency between the
textual specifications of a performance specification and the developed system can
be addressed.

4.2.2 Validation of specifications and verification
of designs

The use of simulations for the validation of specifications and for the verification
of designs of mechatronic and micromechatronic systems is the main theme of
this work. A simulator exists for virtually all hardware description languages and,
for some, several simulators are even available. The simulation of digital hardware
description languages has developed from logic simulation, whilst the simulation of
analogue hardware description languages has developed from circuit simulation.
Hardware description languages that include both digital and analogue compo-
nents are represented on an appropriate ‘mixed mode’ simulator, which spares the
user from having to think about the coupling between digital and analogue sim-
ulator cores. Nevertheless, this interface is indispensable because the simulation
procedures for digital and analogue fields are very different, see Sections 2.7.2
and 2.7.3.
As an alternative to simulation we can also use the methods of formal verification
in the digital field. In general, the motivation for this is that the simulation of
systems almost always remains incomplete because it is not possible to play through