8.1.   INTRODUCTION

Embedded software development for control applications consists of two
phases: first modeling, then implementation. Modeling control applications is
usually done by control engineers with support from tools such as Matlab or
MatrixX. While these tools offer limited code-generation facilities, the efficient
implementation of control designs remains a challenging subdiscipline
of software engineering. Control designs impose hard real-time requirements,
which software engineers traditionally meet by tightly coupling model, code,
and platform. We advocate a decoupling of these domains.

Throughout this chapter, the term platform denotes a hardware configuration,
operating system, and communication protocol. Platforms, which may
be distributed, consist of sensors, actuators, CPUs, and networks. Platform-
independent issues include application functionality and timing. In contrast,
platform-dependent issues include scheduling, communication, and physical
performance. The key to automating embedded software development is to
understand the interface between platform-independent and platform-dependent
issues. Such an interface - that is, an abstract programmer’s model for
embedded systems - enables decoupling software design from implementation,
even for distributed platforms and even in the presence of hard
real-time requirements.

Giotto provides an abstract programmer’s model based on the time-triggered
paradigm. In a time-triggered system, communication - from sensors,
between CPUs, to actuators - is triggered by the tick of a notional global
clock. In a distributed system, such a clock can be provided by a clock
synchronization service. The time-triggered architecture (TTA) [1] offers a
hardware and protocol realization of the time-triggered paradigm, thereby
providing a natural platform for a Giotto implementation. The TTA has
recently gained momentum in safety-critical automotive applications, where
timing predictability is essential. While Giotto offers the predictability of
time-triggered systems, it also offers the flexibility of platform independence.
In particular, it is possible to use a clock synchronization service on top of
any real-time communication protocol to implement Giotto. For example,
recently the event-triggered CAN standard has been extended to TTCAN [2],
which includes a clock synchronization service and thus offers another
attractive platform for implementing Giotto.