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Robin P. Clark 2013-02-18 10:56:27 +00:00
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submission_thesis/CH3_FMEA_criticism/copy.tex
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@ -111,22 +111,25 @@ Distributed real time systems are control systems where
smart sensors communicate over a communications bus to smart sensors communicate over a communications bus to
a master controller. a master controller.
% %
Most modern cars follow this pattern and use CANbus~\cite{canspec,can}. Most modern cars follow this information technology pattern and use CANbus~\cite{canspec,can}.
% %
For instance, the throttle pedal will be linked to a sensor to determine how For instance, in a modern car there will be no mechanical linkage from the pedal to the engine, instead the throttle pedal will be linked to a sensor to determine how
far the pedal is pressed. This sensor will be read by a micro-controller, and passed, via CANbus, to the Engine Control Unit (ECU) far the pedal is pressed.
This sensor will be read by a micro-controller, and passed, via CANbus, to the Engine Control Unit (ECU)
which will use that information (along with information from other sensors) to adjust the power required from the engine. which will use that information (along with information from other sensors) to adjust the power required from the engine.
This adjustment could be direct, or could be another CANbus message passed to a micro-controller regulating engine function.
In terms of FMEA, see figure~\ref{fig:distcon}, our reasoning path spans four interface layers of electronics to software. In terms of FMEA, see figure~\ref{fig:distcon}, our reasoning path spans four interface layers of electronics to software.
Traditional FMEA does not cater for the software hardware interface, and here we have the addition complications Traditional FMEA does not cater for the software hardware interface, and here we have the addition complications
%with the additional complications %with the additional complications
of the communications protocol used to transmit data, and the failure mode characteristics of the communications protocol used to transmit data, and the failure mode characteristics
of the communications physical layer. of the communications physical layer.
(figure~\ref{fig:distcon} %(figure~\ref{fig:distcon}
The failure reasoning paths for a typical section of a distributed real time system, mean that traditional FMEA The failure reasoning paths for a distributed real time system, mean traditional FMEA
is almost impossible to perform. is impossible to perform.
% %
The base component failure mode to system failure paradigm is utterly anachronistic in the distributed real time system environment. The base component failure mode to system failure paradigm is
utterly anachronistic in the distributed real time system environment.
\begin{figure}[h] \begin{figure}[h]