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>Updating the ecos.db database</TITLE
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>The <SPAN
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>eCos</SPAN
> Component Writer's Guide</TH
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><A
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>Chapter 3. The CDL Language</TD
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><DIV
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><H1
CLASS="SECT1"
><A
NAME="LANGUAGE.DATABASE">Updating the <SPAN
CLASS="DATABASE"
>ecos.db</SPAN
> database</H1
><P
>The current implementation of the component framework requires that
all packages be present in a single component repository and listed in
that repository's <SPAN
CLASS="DATABASE"
>ecos.db</SPAN
> database. This is not
generally a problem for application developers who can consider the
component repository a read-only resource, except when adding or
removing packages via the administration tool. However it means that
component writers need to do their development work inside a
component repository as well, and update the database with details of
their new package or packages. Future enhancements to the component
framework may allow new components to be developed outside a
repository. </P
><P
>Like most files related to the component framework, the
<SPAN
CLASS="DATABASE"
>ecos.db</SPAN
> database is actually a <SPAN
CLASS="APPLICATION"
>Tcl</SPAN
> script.
Typical package entries would look like this:</P
><TABLE
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>package CYGPKG_LIBC {
alias { "C library" libc clib clibrary }
directory language/c/libc
script libc.cdl
description "
This package enables compatibility with the ISO C standard - ISO/IEC
9899:1990. This allows the user application to use well known standard
C library functions, and in eCos starts a thread to invoke the user
function main()"
}
package CYGPKG_IO_PCI {
alias { "PCI configuration library" io_pci }
directory io/pci
script io_pci.cdl
hardware
description "
This package contains the PCI configuration library."
}</PRE
></TD
></TR
></TABLE
><P
>The <TT
CLASS="LITERAL"
>package</TT
> command takes two arguments, a name and
a body. The name must be the same as in the <TT
CLASS="LITERAL"
>cdl_package</TT
> command in
the package's top-level <SPAN
CLASS="APPLICATION"
>CDL</SPAN
> script. The body can contain the
following five commands: <TT
CLASS="LITERAL"
>alias</TT
>,
<TT
CLASS="LITERAL"
>directory</TT
>, <TT
CLASS="LITERAL"
>script</TT
>,
<TT
CLASS="LITERAL"
>hardware</TT
> and <TT
CLASS="LITERAL"
>description</TT
>.</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>alias</TT
></DT
><DD
><P
>Each package should have one or more aliases. The first alias is
typically used when listing the known packages, because a string like
<TT
CLASS="LITERAL"
>C library</TT
> is a bit easier to read and
understand than <TT
CLASS="VARNAME"
>CYGPKG_LIBC</TT
>. The other aliases are
not used for output, but are accepted on input. For example the
<SPAN
CLASS="APPLICATION"
>ecosconfig</SPAN
> command-line
tool will accept <TT
CLASS="LITERAL"
>add libc</TT
> as an option, as well
as <TT
CLASS="LITERAL"
>add CYGPKG_LIBC</TT
>.</P
></DD
><DT
><TT
CLASS="LITERAL"
>directory</TT
></DT
><DD
><P
>This is used to specify the location of the package relative to the
root of the component repository. It should be noted that in the
current component framework this location cannot be changed in
subsequent releases of the package: if for some reason it is desirable
to install a new release elsewhere in the repository, all the old
versions must first be uninstalled; the database cannot hold two
separate locations for one package.</P
></DD
><DT
><TT
CLASS="LITERAL"
>script</TT
></DT
><DD
><P
>The <TT
CLASS="LITERAL"
>script</TT
> command specifies the location of the
package's top-level <SPAN
CLASS="APPLICATION"
>CDL</SPAN
> script, in other words the one containing the
<TT
CLASS="LITERAL"
>cdl_package</TT
> definition. If the package follows the <A
HREF="package.html#PACKAGE.HIERARCHY"
>directory layout conventions</A
> then
this script will be in the <TT
CLASS="FILENAME"
>cdl</TT
>
sub-directory, otherwise it will be relative to the package's top-level
directory. Again once a release has been made this file should not
change in later releases. In practice the top-level script is generally
named after the package itself, so changing its name is unlikely to be
useful. </P
></DD
><DT
><TT
CLASS="LITERAL"
>hardware</TT
></DT
><DD
><P
>Packages which are tied to specific hardware, for example device
drivers and HAL packages, should indicate this in both the
<TT
CLASS="LITERAL"
>cdl_package</TT
> command of the <SPAN
CLASS="APPLICATION"
>CDL</SPAN
> script and in the database entry.</P
></DD
><DT
><TT
CLASS="LITERAL"
>description</TT
></DT
><DD
><P
>This should give a brief description of the package. Typically the
text for the <SPAN
CLASS="PROPERTY"
>description</SPAN
> property in the <TT
CLASS="LITERAL"
>cdl_package</TT
> command will
be re-used.</P
></DD
></DL
></DIV
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>Most of the information in the <SPAN
CLASS="DATABASE"
>ecos.db</SPAN
> file could
be obtained by a relatively simple utility. This would be passed a
single argument identifying a package's top-level <SPAN
CLASS="APPLICATION"
>CDL</SPAN
> script. The
directory path relative to the component repository root could be
determined from the filename. The name, <TT
CLASS="LITERAL"
>description</TT
>
and <TT
CLASS="LITERAL"
>hardware</TT
> fields could be obtained from the
script's <TT
CLASS="LITERAL"
>cdl_package</TT
> command. The <SPAN
CLASS="PROPERTY"
>display</SPAN
> property would supply
the first alias, additional aliases could be obtained by extending the
syntax of that property or by other means. Something along these lines
may be provided by a future release of the component framework.</P
></BLOCKQUOTE
></DIV
><P
>Currently the <SPAN
CLASS="DATABASE"
>ecos.db</SPAN
> database also holds
information about the various targets. When porting to a new target it
will be necessary to add information about the target to the database,
as well as the details of the new platform HAL package and any related
packages. </P
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