How to Invoke Simics API inside GEMS

In order to use Simics API, there are a few places that need to be modified in GEMS.
First, all the Simics API calls are put in a dummy place holding spot, in $GEMS/ruby/simics/simics_api_dummy.c. In this file, all the data types and methods involved in calling Simics API are decleared and dummily defined. If your Simics API method is not defined here, you will have trouble using it.
Second, it is a good practice to wrap up all Simics API calls into GEMS's style Simics API calls. To find a few of GEMS's style Simics API calls, look at $GEMS/ruby/simics/Interface.h/C. There are a bunch of examples. GEMS's style Simics API calls usually have different parameter type than the original Simics API. Usually, it is more simplified than original Simics API.
To summarize, adding Simics API calls is not hard, it requires some dummy place holder in $GEMS/ruby/simics/simics_api_dummy.c, which could be tricky to find.