Page 94 - Mechatronic Systems Modelling and Simulation with HDLs

5

Software in Hardware

Description Languages

5.1 Introduction

A whole range of methods can be listed for the joint simulation of hardware
and software, which are concisely summarised by Rowson in [355]. The most
important criteria here are: precision with regard to timing; simulation speed; the
availability of models; and the possibility of debugging the simulated software.
The simulation speed and timing precision are normally in competition with one
another. The approaches described in what follows provide various compromises
in this context, see Table 5.1.
The most precise, but consequently also the most expensive, simulation option is
to describe the processor core in question with such accuracy that the signal timing
is reproduced exactly at the connections. The software is available as information
in the storage model and is processed during the simulation of hardware. This
particularly exact modelling is associated with the longest running times.
We can abstract from this model and demand only that the signals at the termi-
nals are correct at every active edge of the clock signal. This can firstly simplify
the model, because for the most part the signal delays can be disregarded in a
synchronously executed processor core. Furthermore, the number of simulation
events is significantly reduced in comparison to the precise timing. Both lead to a
significant acceleration of the simulation.
In the next step we can move to the modelling of the command set and its
execution. In this procedure the values are correctly illustrated in the registers and
in the memory but details such as the pipelining of instructions may be neglected.
As a result a large part of the timing information is lost.
The approaches described up to this point each require suitable processor models.
However, techniques exist that do not necessitate the modelling of the hardware.
This is the case firstly if the communication between software and hardware runs
asynchronously and the time between the communications thus plays no role. In
this case it is sufficient to compile the software for the simulation workstation and

Mechatronic Systems Georg Pelz
 2003 John Wiley & Sons, Ltd ISBN: 0-470-84979-7