View CCA_TOOLS_ROOT/share/cca-spec-babel-0_8_0-babel-1.0.0/cca.sidl. First, notice the package declarations at the beginning of the file:

package gov {
package cca version 0.8.0 {
...

which declare the gov.cca namespace for everything in the file.

Now, search for “interface Component”:

...
    /**
     * All components must implement this interface.
     */
    interface Component {
        ... Comments elided ...
        void setServices(in Services services) throws CCAException;
    }
...

Which tells us that our driver will have to implement a setServices. This is the key method that allows a piece of code to become a CCA component. The component's setServices method is invoked by the CCA framework when the component is instantiated, and advertises to the framework the ports the component will provide and use.

Since the port this component provides is also part of the CCA specification, this is the place to look for the definition of the GoPort. Search for “interface GoPort”:

...
    package ports {

        /**
         * Go, component, go!
         */
        interface GoPort extends Port {
            ... Comments elided ...
            int go();
        }
...

First, notice that there is an additional package declaration here, making the full name of this interface gov.cca.ports.GoPort. This definition tells us that our driver component must also implement a go method.

Now you have enough information to write the SIDL declaration for your driver component. At this point, you should choose whether you want to implement your driver component in C++ or Fortran 90. (Once you get one done, you can implement the other too, if you wish.)

Edit the file $STUDENT_SRC/components/sidl/drivers.sidl and type in one of the two following SIDL declarations, according to your choice of language:

1. package drivers version 1.0 {
     class F90Driver implements gov.cca.ports.GoPort,
                                    gov.cca.Component
     {
        int go();
        void setServices(in gov.cca.Services services) 
                         throws gov.cca.CCAException;
     }
   }
   

2. package drivers version 1.0 {
     class CXXDriver implements gov.cca.ports.GoPort,
                                    gov.cca.Component
     {
        int go();
        void setServices(in gov.cca.Services services) 
                         throws gov.cca.CCAException;
     }
   }
   

First, notice that the two declarations are identical except for the name, and in reality, you could choose anything you wanted for the name. The only reason we put an indication of the implementation language into the class name of this component was pedagogical: to avoid a name collision if you want to eventually implement both versions, and identify what distinguishes them. Normally, you might want different implementations of a component if they do things differently (i.e. use different algorithms), or in the case of a driver, solve different problems. Under normal circumstances, there is no reason to have more than one implementation of a component that does precisely the same thing (though it is common to have multiple implementations that do things in somewhat different ways, but with the same result).

Second, notice that the class definition references both gov.cca.ports.GoPort and gov.cca.Component, and declares all of the methods that we saw in those interface definitions, with precisely the same signatures.

Now you need to modify the Makefile system so that it is aware of the new component you're adding (the drivers.sidl is already listed there along with other .sidl files).

Edit $STUDENT_SRC/component/MakeIncl.components and make the following additions:

# SIDL files containing component declarations
# For example:
# SIDL_FILES = sidl/drivers.sidl
SIDL_FILES = sidl/functions.sidl sidl/integrators.sidl sidl/randomgens.sidl \
	sidl/drivers.sidl sidl/unitdrivers.sidl sidl/library.sidl

# The COMPONENTS list contains the fully-qualified names of the component
# classes, augmented with -LANGUAGE, where LANGUAGE is the language
# in which the component is implemented, e.g., c, cxx, f90.
# For example:
# COMPONENTS = drivers.F90Driver-f90 drivers.CXXDriver-cxx
COMPONENTS = drivers.PYDriver-python functions.PiFunction-cxx \
library.CxxUnitsLibraryComp-cxx library.PyUnitsLibraryComp-python \
undrivers.PyDriver-python \
functions.LinearFunction-c integrators.MonteCarlo-f90 \
randomgens.RandNumGenerator-cxx  integrators.Trapezoid-cxx \
        integrators.Simpson-f77\
        drivers.CXXDriver-cxx

Of course if you've chose to create the Fortran 90 driver, you should add drivers.F90Driver-f90 to the definition of COMPONENTS instead. In both cases, notice the backslash (“\”) used to continue definition on to the next line. make will accept long lines, but the files are easier to read if they're nicely formatted.

	Important
	Before proceeding, you need to be sure that you have done the initial build of the student-src, following the directions in Appendix C, Building the Tutorial and Student Code Trees.

When it is processing a .sidl file, Babel needs to be able to resolve external references contained within the file (for example, to gov.cca.Component, or to other ports, etc.). The simplest way to do this is to have Babel collect all of the information it needs in a repository. The build system for the tutorial is designed to do this, so at this point, we need to add the new drivers.sidl file to the repository.

In the $STUDENT_SRC/components directory, type make .repository to make Babel process the .sidl files and update the XML repository. The output should look something like this:

touch .sidl

### Generating XML for SIDL packages containing component declarations
/san/cca/cca-tools_gcc_intelF90_PIC/bin/babel -t xml -R../xml_repository \
    -R/san/cca/cca-tools_gcc_intelF90_PIC/share/ \
     cca-spec-babel-0_8_0-babel-1.0.0/xml  \
     -o ../xml_repository sidl/functions.sidl sidl/integrators.sidl \
     sidl/randomgens.sidl sidl/drivers.sidl sidl/unitdrivers.sidl \
     sidl/library.sidl
Babel: Parsing URL "file:/san/homedirs/bernhold/student-src/ \
	components/sidl/functions.sidl".
Babel: Parsing URL "file:/san/homedirs/bernhold/student-src/ \
	components/sidl/integrators.sidl".
Babel: Parsing URL "file:/san/homedirs/bernhold/student-src/ \
	components/sidl/randomgens.sidl".
Babel: Parsing URL "file:/san/homedirs/bernhold/student-src/ \
	components/sidl/drivers.sidl".
Babel: Parsing URL "file:/san/homedirs/bernhold/student-src/ \
	components/sidl/unitdrivers.sidl".
Babel: Parsing URL "file:/san/homedirs/bernhold/student-src/ \
	components/sidl/library.sidl".
touch .repository