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><A
NAME="CDL-CONFLICTS">Conflicts</H1
><P
>Not all settings of configuration items will lead to a
	  coherent configuration; for example, the use of a timeout
	  facility might require the existence of timer support, so if
	  the one is required the other cannot be removed.  Coherence
	  is policed by means of consistency rules (in particular, the
	  goal expressions that appear as CDL items
	  <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>requires</I
></SPAN
> and
	  <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>active_if</I
></SPAN
> attributes [see
	  above]).  A violation of consistency rules creates a
	  <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>conflict</I
></SPAN
>, which must be resolved in
	  order to ensure a consistent configuration. Conflict
	  resolution can be performed manually or with the assistance
	  of the <SPAN
CLASS="PRODUCTNAME"
>eCos</SPAN
> tools.  Conflicts come in the following
	  flavors:</P
><P
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><P
>An <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>unresolved</I
></SPAN
> conflict means that
there is a reference to an entity that is not yet in the current
configuration </P
></LI
><LI
><P
>An <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>illegal value</I
></SPAN
> conflict is caused
when a configuration item is set to a value that is not permitted
(that is, a <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>legal_values</I
></SPAN
> goal expression
is failing) </P
></LI
><LI
><P
>An <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>evaluation exception</I
></SPAN
> conflict
is caused when the evaluation of an expression would fail (for example,
because of a division by zero) </P
></LI
><LI
><P
>An <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>unsatisfied goal</I
></SPAN
> conflict is caused
by a failing <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>requires</I
></SPAN
> goal expression </P
></LI
><LI
><P
>A <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>bad data</I
></SPAN
> conflict arises only rarely,
and corresponds to badly constructed CDL.  Such a conflict can only
be resolved by reference to the CDL writer.</P
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