Redundancy in Fault Tolerant Embedded Systems



 There are three main types of redundancy used in embedded systems:

  • Standby redundancy uses two or more identical components, with one of the components being in standby mode. If the active component fails, the standby component is automatically activated. This type of redundancy is simple to implement and relatively inexpensive, but it does not provide full fault tolerance.
  • N-modular redundancy (NMR) uses multiple identical components, with the output of each component being voted on to determine the correct result. This type of redundancy provides better fault tolerance than standby redundancy, but it is more complex and expensive to implement.
  • 1:N redundancy uses one primary component and multiple backup components. The primary component is used for normal operation, but if it fails, one of the backup components is activated. This type of redundancy is more complex than standby redundancy, but it can provide better fault tolerance.

Here is a more detailed description of each type of redundancy:

  • Standby redundancy
    • This type of redundancy uses two or more identical components, with one of the components being in standby mode.
    • The standby component is not used for normal operation, but it is powered up and ready to be activated if the active component fails.
    • When the active component fails, a watchdog timer is used to detect the failure.
    • The watchdog timer then activates the standby component.
    • This type of redundancy is simple to implement and relatively inexpensive, but it does not provide full fault tolerance.
  • N-modular redundancy (NMR)
    • This type of redundancy uses multiple identical components, with the output of each component being voted on to determine the correct result.
    • For example, in triple modular redundancy (TMR), three identical components are used.
    • The output of each component is voted on, and the majority vote is used as the final output.
    • This type of redundancy provides better fault tolerance than standby redundancy, but it is more complex and expensive to implement.
  • 1:N redundancy
    • This type of redundancy uses one primary component and multiple backup components.
    • The primary component is used for normal operation, but if it fails, one of the backup components is activated.
    • This type of redundancy is more complex than standby redundancy, but it can provide better fault tolerance.

The type of redundancy that is used in an embedded system depends on the criticality of the application. For example, a life-critical application would require a high level of fault tolerance, so N-modular redundancy or 1:N redundancy would be used. For a less critical application, standby redundancy might be sufficient.

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