Fault Avoidance and Fault Tolerance

Jabez Winston C15MU01

1st year M.E Embedded and Real-Time SystemsPSG College of Technology

WaferA wafer is a thin slice of semiconductor

material, such as a crystalline silicon, used in electronics for the fabrication of integrated circuits.

2-inch (51 mm), 4-inch (100 mm), 6-inch (150 mm), and 8-inch (200 mm) wafers

DieA die in the context of integrated circuits is a

small block of semiconducting material, on which a given functional circuit is fabricated

Die

Intel Xeon processor E7440 die containing 1.9 billion transistors.

Die is 22×23 mm (503 mm2)

Inside IC packaging

Die

VLSI circuits like microprocessor contains billions of transistors with feature size in order of nanometers.

So chances of failure are very high.

Even if the digital system is designed and manufactured without faults , the system can develop faults at later stages.

Faults, Errors and Failures• Fault: A physical defect within a circuit or a system– May or may not cause a system failure

• Error: Manifestation of a fault that results in incorrectcircuit (system) outputs or states– Caused by faults

• Failure: Deviation of a circuit or system from itsspecified behavior– Fails to do what it should do– Caused by an error

• Fault ---> Error ---> Failure

Some Real Defects in Chips• Processing Faults• Material Defects• Time-Dependent Failures• Packaging Failures

Fault avoidanceFault avoidance (a process oriented concept)

seeks to prevent faults from being introduced into the system

By carefully designing and manufacturing systems , fault can be avoided

Fault toleranceFault tolerance (a product oriented concept)

accepts faults in a limited capacity and masks their manifestation

A fault-tolerant design enables a system to continue its intended operation, possibly at a reduced level, rather than failing completely, when some part of the system fails.

Methods to avoid faults and building fault tolerant systems

RedundancyIt can implemented in the following ways

Providing multiple identical instances of the same system or subsystem, directing tasks or requests to all of them in parallel.

Providing multiple identical instances of the same system and switching to one of the remaining instances in case of a failure .

 Providing multiple different implementations of the same specification

Thank you !