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+><TITLE
+>Conflicts and constraints</TITLE
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+TITLE="Manual Configuration"
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+>eCos User Guide</TH
+></TR
+><TR
+><TD
+WIDTH="10%"
+ALIGN="left"
+VALIGN="bottom"
+><A
+HREF="creating-build-tree.html"
+ACCESSKEY="P"
+>Prev</A
+></TD
+><TD
+WIDTH="80%"
+ALIGN="center"
+VALIGN="bottom"
+>Chapter 28. Manual Configuration</TD
+><TD
+WIDTH="10%"
+ALIGN="right"
+VALIGN="bottom"
+><A
+HREF="building-the-system.html"
+ACCESSKEY="N"
+>Next</A
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+><HR
+ALIGN="LEFT"
+WIDTH="100%"></DIV
+><DIV
+CLASS="SECT1"
+><H1
+CLASS="SECT1"
+><A
+NAME="CONFLICTS-AND-CONSTRAINTS">Conflicts and constraints</H1
+><P
+>Configuration options are not completely independent. For example
+the C library's <TT
+CLASS="FUNCTION"
+>strtod()</TT
+> and <TT
+CLASS="FUNCTION"
+>atof()</TT
+>
+functions rely on the math library package to provide certain functionality. If the math library package is removed then the C
+library can no longer provide these functions. Each package describes constraints like these in CDL <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>"requires"</I
+></SPAN
+> properties. If a constraint is not satisfied, then the configuration contains a conflict. For any given conflict there can
+be several resolution options. For example, it would be possible to add the math library package back to the
+configuration, or to disable the <TT
+CLASS="FUNCTION"
+>strtod()</TT
+> and <TT
+CLASS="FUNCTION"
+>atof()</TT
+> functions.</P
+><P
+>The <SPAN
+CLASS="PRODUCTNAME"
+>eCos</SPAN
+> configuration tools will report any conflicts in the current configuration. If there are any such conflicts
+then the configuration is usually unsafe and it makes no sense to build and run <SPAN
+CLASS="PRODUCTNAME"
+>eCos</SPAN
+> in such circumstances. In fact,
+any attempt at building <SPAN
+CLASS="PRODUCTNAME"
+>eCos</SPAN
+> is likely to fail. In exceptional cases it is possible to override this by using e.g. the
+<TT
+CLASS="OPTION"
+>--ignore-errors</TT
+> qualifier with ecosconfig. </P
+><P
+>Many constraints are fairly simple in nature, and the configuration tools contain an inference engine which can
+resolve the associated conflicts automatically. For example, if the math library package is removed then the
+inference engine can resolve the resulting conflict by disabling the configuration option for <TT
+CLASS="FUNCTION"
+>strtod()</TT
+> and <TT
+CLASS="FUNCTION"
+>atof()</TT
+>. All
+such changes will be reported. Sometimes the inference engine cannot resolve a conflict, for example it is not
+allowed to override a change that has been made explicitly by the user. Sometimes it will find a solution which does
+not match the application's requirements. </P
+><P
+>A typical session involving conflicts would look something like this:
+<TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+>$ ecosconfig new pid</PRE
+></TD
+></TR
+></TABLE
+>This creates a new configuration with the default template. For most targets this will not result in any conflicts,
+because the default settings for the various options meet the requirements of the default template.</P
+><P
+> For some targets
+there may be conflicts and the inference engine would come into play.
+<TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+>$ ecosconfig remove libm
+U CYGSEM_LIBC_STDIO_SCANF_FLOATING_POINT, new inferred value 0
+U CYGFUN_LIBC_strtod, new inferred value 0
+U CYGSEM_LIBC_STDIO_PRINTF_FLOATING_POINT, new inferred value 0 </PRE
+></TD
+></TR
+></TABLE
+>
+ecosconfig reports that this change caused three conflicts, all in the C library. The inference engine was able to
+resolve all the conflicts and update the relevant configuration options accordingly. </P
+><P
+>To suppress the inference engine <TT
+CLASS="OPTION"
+>--no-resolve</TT
+> can be used:
+<TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+>$ ecosconfig new pid
+$ ecosconfig --no-resolve remove libm
+C CYGSEM_LIBC_STDIO_SCANF_FLOATING_POINT, "requires" constraint not satisfied: CYGPKG_LIBM
+C CYGSEM_LIBC_STDIO_PRINTF_FLOATING_POINT, "requires" constraint not satisfied: CYGPKG_LIBM
+C CYGFUN_LIBC_strtod, "requires" constraint not satisfied: CYGPKG_LIBM </PRE
+></TD
+></TR
+></TABLE
+>
+Three unresolved conflicts are reported.</P
+><P
+>The <B
+CLASS="COMMAND"
+>check</B
+> command can be used to get the current state of the
+configuration, and the <TT
+CLASS="OPTION"
+>--verbose</TT
+> qualifier will provide additional information: </P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+>$ ecosconfig --srcdir /home/bartv/ecc/ecc --verbose check
+Target: pid
+Template: default
+Removed:
+ CYGPKG_LIBM
+3 conflict(s):
+C CYGFUN_LIBC_strtod, "requires" constraint not satisfied: CYGPKG_LIBM
+ Possible solution:
+ CYGFUN_LIBC_strtod -> 0
+ CYGSEM_LIBC_STDIO_SCANF_FLOATING_POINT -> 0
+C CYGSEM_LIBC_STDIO_PRINTF_FLOATING_POINT, "requires" constraint not satisfied: CYGPKG_LIBM
+ Possible solution:
+ CYGSEM_LIBC_STDIO_PRINTF_FLOATING_POINT -> 0
+C CYGSEM_LIBC_STDIO_SCANF_FLOATING_POINT, "requires" constraint not satisfied: CYGPKG_LIBM
+ Possible solution:
+ CYGSEM_LIBC_STDIO_SCANF_FLOATING_POINT -> 0 </PRE
+></TD
+></TR
+></TABLE
+><P
+>If the proposed solutions are acceptable, the resolve command can be used to apply them:
+<TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+>$ ecosconfig resolve
+U CYGSEM_LIBC_STDIO_SCANF_FLOATING_POINT, new inferred value 0
+U CYGFUN_LIBC_strtod, new inferred value 0
+U CYGSEM_LIBC_STDIO_PRINTF_FLOATING_POINT, new inferred value 0 </PRE
+></TD
+></TR
+></TABLE
+></P
+><P
+>The current configuration is again conflict-free and it is possible to generate a build tree. The <TT
+CLASS="OPTION"
+>--quiet</TT
+> qualifier can
+be used to suppress the change messages, if desired.</P
+><P
+>When changing individual configuration options by editing the ecos.ecc file (as described below), the resulting
+system should be checked and any problems should be resolved. For example, if CYGFUN_LIBC_strtod is
+explicitly enabled in the savefile:
+<TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+>$ edit ecos.ecc
+$ ecosconfig check
+Target: pid
+Template: default
+Removed:
+ CYGPKG_LIBM
+1 conflict(s):
+C CYGFUN_LIBC_strtod, "requires" constraint not satisfied: CYGPKG_LIBM
+$ ecosconfig resolve
+C CYGFUN_LIBC_strtod, "requires" constraint not satisfied: CYGPKG_LIBM </PRE
+></TD
+></TR
+></TABLE
+>
+In this case the inference engine cannot resolve the conflict automatically because that would involve changing a
+user setting. Any attempt to generate a build tree will fail:
+<TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+>$ ecosconfig --srcdir /home/bartv/ecc/ecc tree
+C CYGFUN_LIBC_strtod, "requires" constraint not satisfied: CYGPKG_LIBM
+Unable to generate build tree, this configuration still contains conflicts.
+Either resolve the conflicts or use --ignore-errors </PRE
+></TD
+></TR
+></TABLE
+></P
+><P
+>It is still possible to generate a build tree:
+<TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="SCREEN"
+>$ ecosconfig --srcdir /home/bartv/ecc/ecc --ignore-errors tree
+C CYGFUN_LIBC_strtod, "requires" constraint not satisfied: CYGPKG_LIBM
+$ make </PRE
+></TD
+></TR
+></TABLE
+>
+In this case <SPAN
+CLASS="PRODUCTNAME"
+>eCos</SPAN
+> will fail to build. In other cases of unresolved conflicts <SPAN
+CLASS="PRODUCTNAME"
+>eCos</SPAN
+> may build, but may not run. In
+general all conflicts should be resolved by editing the <TT
+CLASS="FILENAME"
+>ecos.ecc</TT
+> file, by letting the inference engine make appropriate
+changes, or by other means, before any attempt is made to build or run <SPAN
+CLASS="PRODUCTNAME"
+>eCos</SPAN
+>. </P
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