Page 24 - Mechatronic Systems Modelling and Simulation with HDLs

2.3 FIELDS OF APPLICATION 13

First of all it raises the question of its validity, i.e. whether the described system
really corresponds with the desired system. Furthermore, it is doubtful whether
a given (paper) specification is completely and unambiguously formulated. These
questions can only be answered in a systematic manner when the transition is made
to an implementable specification, which can then be validated by simulation, for
example. A further advantage of this transition lies in the possibility of the veri-
fication of the individual design stages against the specification. Furthermore, this
opens up the opportunity of performing a formal verification against the specifi-
cation. In digital electronics, behavioural modelling as a specification is becoming
increasingly prevalent, in all other domains it is still at a very early stage.
Modelling for a specification is pure behavioural modelling, which — as is the
case for a paper specification — may not anticipate the implementation. For a
microprocessor, for example, a specification would describe only the instruction
set and the associated actions. The way that the individual operations are realised
cannot be the object of the specification. An executable specification for a memory
module may consist of a large array for the memory content and some logic for
the processing of read and write processes. The specification of an A/D converter
could formulate the pure translation of analogue values into digital values and the
resulting delay.

2.3.6 Modelling for the design

Modelling for the checking of technical system designs for each simulation is the
classic application case. All engineering-science disciplines use simulation benefi-
cially to this end.
This applies particularly in microelectronics. A manufacturing run typically lasts
6–12 weeks and is associated with significant costs. Repairs to manufactured chips
are more or less impossible. Under such boundary conditions, one cannot afford
to iterate the manufacturing process to rectify design errors. Instead, it is neces-
sary to enter manufacture with a fundamentally error-free design, which — given
the complexities that are currently possible, involving some tens of millions of
transistors — cannot be achieved without simulation.
If we consider discretely structured printed circuit boards, then it is slightly less
critical that the circuit is fully checked in advance by simulation. The etching and
fitting of circuit boards is significantly simpler and quicker than chip manufacture.
Changes can be performed comparatively easily. The circuits are also less complex
by orders of magnitude. So it can be worthwhile to solder a circuit together as a
bread-board arrangement and check it by measurement. Nevertheless, the perfor-
mance of virtual experiments on a computer is generally quicker and cheaper than
the real experiment in the laboratory.
For software, things are comparatively simple. The compilation of software can
be regarded as rudimentary modelling, as software is executable after this stage, i.e.
it is simulatable. The simulation sequence and the simulation result are normally