Dependable Memory - Laboratoire Interface Capteurs ...

Chapter 1
Dependability and Fault Tolerance
t is a complex task to design embedded systems for critical real-time applications. Such systems
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must not only guarantee to meet hard real-time deadlines imposed by their physical environment,
but also guarantee to do so dependably, despite the occurrence of faults [Pow10]. The need of fault
tolerant (FT) computing is becoming more and more important in recent years [Che08] and likely
become the norm. In the past, FT was the exclusive domain of very specialized applications like
safety critical systems. However modern design trends are making circuits more sensitive and now
all real-time systems should have at least some FT features. Therefore, FT is an important need of the
time.
Modern social system is hinged to automated industry. In some sensitive industrial sectors, even a
single fault can result in a million dollar loss (e.g. in banking and stock markets) or can result in loss
of life (e.g. air traffic control system). Industries like automotive, avionics, and energy production re-
quire availability, performance and real-time response ability to avoid catastrophic failures. In table 1,
cost per hour for the failure of the control systems has been compared to show the importance/demand
of FT in the industrial sector.
Table 1.1: Cost/hour for failure of control system [Pie07]
Application Domain Cost (Euro/hour)
Cell-phone Operator 40k
Airline Reservation 90k
ATM Machine (Banking) 2.5M
Automobile Assembling Unit 6M
Stock Transaction 6.5M
Most of these system (in table 1) rely on embedded systems. The design of the FT processor
is one of the basic requirement for dependable embedded applications. Accordingly, we propose to
design a fault tolerant processor to eliminate (tolerate) transient faults that result from SEUs. In this
introductory chapter, we will address the basic concepts and terminologies related to fault tolerant
computing. This chapter is divided into three main parts: the first part will be arguing the current
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