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>Conflicts</TITLE
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TITLE="Configuration Items"
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>eCos User Guide</TH
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>Prev</A
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><TD
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>Chapter 24. CDL Concepts</TD
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="CDL-CONFLICTS">Conflicts</H1
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><P
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>Not all settings of configuration items will lead to a
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          coherent configuration; for example, the use of a timeout
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          facility might require the existence of timer support, so if
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          the one is required the other cannot be removed.  Coherence
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          is policed by means of consistency rules (in particular, the
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          goal expressions that appear as CDL items
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          <SPAN
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><I
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>requires</I
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> and
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          <SPAN
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><I
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>active_if</I
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> attributes [see
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          above]).  A violation of consistency rules creates a
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          <SPAN
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><I
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>conflict</I
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>, which must be resolved in
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          order to ensure a consistent configuration. Conflict
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          resolution can be performed manually or with the assistance
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          of the <SPAN
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CLASS="PRODUCTNAME"
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>eCos</SPAN
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> tools.  Conflicts come in the following
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          flavors:</P
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></P
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><LI
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><P
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>An <SPAN
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><I
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>unresolved</I
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> conflict means that
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there is a reference to an entity that is not yet in the current
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configuration </P
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></LI
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><LI
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><P
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>An <SPAN
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><I
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>illegal value</I
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></SPAN
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> conflict is caused
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when a configuration item is set to a value that is not permitted
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(that is, a <SPAN
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><I
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>legal_values</I
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> goal expression
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is failing) </P
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><LI
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>An <SPAN
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><I
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>evaluation exception</I
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> conflict
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is caused when the evaluation of an expression would fail (for example,
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because of a division by zero) </P
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><LI
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>An <SPAN
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>unsatisfied goal</I
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> conflict is caused
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by a failing <SPAN
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>requires</I
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> goal expression </P
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>A <SPAN
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><I
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>bad data</I
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> conflict arises only rarely,
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and corresponds to badly constructed CDL.  Such a conflict can only
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be resolved by reference to the CDL writer.</P
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