When you use the Virtual Developer IDE to develop code generators, you run your generators in a separate Java process on your development computer. That separate process is an OSGi container (Equniox). In Virtual Developer speak such an OSGi container is called a “Generation Unit”. The dialog for Eclipse run configurations has a category “GenerationUnit” that allows you to define such generation units. When you define a generation unit you can select the generators that are defined within your workspace. For each virtualdeveloper.genset file in your workspace projects you will find an entry to select from.
In order to be sure to use the correct OSGi bundles for the generator development, you can use a target definition and set it as the target platform to be used by Eclipse.
By doing so, you can be sure that Eclipse uses that target definition also for the execution of your generation unit (as a run configuration).