These topics are useful only if you have a source release of the development kit. The src folder under JC_CONNECTED_HOME contains all of the source files for the RI including VM code, and all tools (such as the packager and installer). You can modify or add to these files and build a customized Java Card 3 platform reference implementation (RI) according to your specific requirements. The following are possible reasons that you might have for building a custom RI:
Add additional classes or packages if a proprietary API or other implementation classes are used.
Fine tune the existing sources.
Update tools to work with target platform.
ROMize the applications. ROMizing masks applications into the cjcre.exe.