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>Conflicts and constraints</TITLE
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><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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