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Safety Assessment and Fault Tree Analysis for Embedded Software in Critical Applications

This document discusses the techniques and methods for safety assessment in embedded software design, focusing on Fault Trees and probabilistic reasoning to identify hazards that could lead to incidents or mishaps. It elaborates on the relationships between primary, undeveloped, and external events, utilizing fault trees and event trees for thorough analysis. The aim is to estimate the consequences of these events and ensure reliability, targeting a probability of failure (PFH) of less than 10^-6 per hour. This work is essential for the development of safe, reliable, and efficient software in critical systems.

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Safety Assessment and Fault Tree Analysis for Embedded Software in Critical Applications

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  1. Safety Assessment (Fault Trees) ITV Model-based Analysis and Design of Embedded Software Techniques and methods for Critical Software Anders P. Ravn Aalborg University August 2011

  2. Safety Assessment Find hazardsthat may lead to incidents or mishaps, analyze their relations, and estimate their consequences. May involve probabilistic reasoning (Reliability Engineering). Is PFH < 10-6 per hour (h-1 ) ?

  3. Techniques • Fault Trees • Event tree (forward analysis from initiating event) • Combinations (cause-consequence diagrams) Many tools Kirsten M. Hansen, Anders P. Ravn and Victoria Stavridou, From Safety Analysis to Formal Specification, IEEE Trans. Softw. Eng.24,pp. 573-584, July 1998

  4. Primary Events: Basic event – fault in atomic component Undeveloped Event – fault in composite component (may be analyzed later) External event – expected event from environment Intermediate event: Nodes inside a fault-tree Fault Trees - Events

  5. ... ... Fault Tree - Gates condition Inhibit gate

  6. Example – ”Woke too late” Woke too late ”Inner clock” fails Phone fails Alarm clock fails

  7. Example ”Alarm clock fails” Alarm clock fails Power fails Beeper fails Button fails electronics fail SW fails Beeper not set Button read fails

  8. Cut Set A cut set is a set of events that causes a top level event A singleton cut set is a single point of failure

  9. Example – ”Wake too late” Wake too late ”Inner clock” fails Phone fails Alarm clock fails

  10. Example ”Alarm clock fails” Alarm clock fails Power fails Beeper fails Button fails electronics fail SW fails Beeper not set Button read fails

  11. Exercise – estimate the PFD Alarm clock fails Power fails Beeper fails Button fails electronics fail SW fails Beeper not set Button read fails

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