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sneaky snoopy

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Robin Clark 2012-11-22 11:54:09 +00:00
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19
submission_thesis/CH5_Examples/software.tex
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@ -33,7 +33,8 @@ When we have analysed a software function---using failure conditions
of its inputs as failure modes---we can of its inputs as failure modes---we can
determine its symptoms of failure (i.e. how calling functions will see its failure mode behaviour). determine its symptoms of failure (i.e. how calling functions will see its failure mode behaviour).
We can thus apply the $\derivec$ process to software functions, by viewing them in terms of their failure We can thus apply the FMMD % $\derivec$
process to software functions, by viewing them in terms of their failure
mode behaviour. To simplify things as well, software already fits into a hierarchy. mode behaviour. To simplify things as well, software already fits into a hierarchy.
For Electronics and Mechanical systems, although we may be guided by the original designers For Electronics and Mechanical systems, although we may be guided by the original designers
concepts of modularity and sub-systems in design, applying FMMD means deciding on the members for {\fgs} concepts of modularity and sub-systems in design, applying FMMD means deciding on the members for {\fgs}
@ -410,8 +411,8 @@ With these failure modes, we can analyse our first functional group, see table~\
We now collect the symptoms for the hardware functional group, $\{ HIGH , LOW, V\_ERR \} $. We now collect the symptoms for the hardware functional group, $\{ HIGH , LOW, V\_ERR \} $.
We now create a {\dc} to represent this called $CMATV$. We now create a {\dc} to represent this called $CMATV$.
We can express this using the `$\derivec$' function thus: %We can express this using the `$\derivec$' function thus:
$$ CMATV = \; \derivec (G_1) .$$ %$$ CMATV = \; \derivec (G_1) .$$
As its failure modes, are the symptoms of failure from the functional group we can now state: As its failure modes, are the symptoms of failure from the functional group we can now state:
$$fm ( CMATV ) = \{ HIGH , LOW, V\_ERR \} .$$ $$fm ( CMATV ) = \{ HIGH , LOW, V\_ERR \} .$$
@ -502,9 +503,9 @@ for the function.
This postcondition, {\em /* ensure: value is voltage input to within 0.1\% */ }, This postcondition, {\em /* ensure: value is voltage input to within 0.1\% */ },
corresponds to $VV\_ERR$, and is already in the {\fm} set for this {\fg}. corresponds to $VV\_ERR$, and is already in the {\fm} set for this {\fg}.
We can now create a {\dc} called $RADC$ thus: $$RADC = \; \derivec(G_2)$$ which has the following %We can now create a {\dc} called $RADC$ thus: $$RADC = \; \derivec(G_2)$$ which has the following
{\fms}: %{\fms}:
We can now create a {\dc} called $RADC$ thus:
$$ fm(RADC) = \{ VV\_ERR, HIGH, LOW \} .$$ $$ fm(RADC) = \{ VV\_ERR, HIGH, LOW \} .$$
@ -575,9 +576,9 @@ For single failures these are the two ways in which this function
can fail. An $OUT\_OF\_RANGE$ will be flagged by the error flag variable. can fail. An $OUT\_OF\_RANGE$ will be flagged by the error flag variable.
The $VAL\_ERR$ will simply mean that the value read is incorrect. The $VAL\_ERR$ will simply mean that the value read is incorrect.
We can finally make a {\dc} to represent a failure mode model for our function $read\_4\_20\_input$ thus: We can finally make a {\dc} to represent a failure mode model for our function $read\_4\_20\_input$. %thus:
$$ R420I = \; \derivec(G_3) .$$ % $$ R420I = \; \derivec(G_3) .$$
This new {\dc} has the following {\fms}: This new {\dc} has the following {\fms}:
$$fm(R420I) = \{OUT\_OF\_RANGE, VAL\_ERR\} .$$ $$fm(R420I) = \{OUT\_OF\_RANGE, VAL\_ERR\} .$$
@ -612,7 +613,7 @@ as a hierarchical diagram, see figure~\ref{fig:eulerswhw}. % see figure~\ref{fig
\end{figure} \end{figure}
% HTR == HATE TO REMOVE
%HTR 18NOV2012 We can represent %the hierarchy in figure~\ref{fig:hd} algebraically, %HTR 18NOV2012 We can represent %the hierarchy in figure~\ref{fig:hd} algebraically,
%HTR 18NOV2012 the analysis hierarchy algebraically using the `$\derivec$' function: %HTR 18NOV2012 the analysis hierarchy algebraically using the `$\derivec$' function:
%HTR 18NOV2012 %using the groups as intermediate stages: %HTR 18NOV2012 %using the groups as intermediate stages: