After building and installing the Ada cross compiler you need a basic run time system (RTS).
After unpacking the AVR-Ada source distribution, run configure and make in the top level directory. Configure determines the installation path (PREFIX) from the installed gcc. See the comments in the Makefile for the different make targets. You should first build and install the RTS, then the AVR libraries. The RTS will be installed in the gcc tree, the AVR libraries will be installed in PREFIX/avr/ada. Make sure that you have write permissions in these locations.
configure make build_rts make install_rts make build_libs make install_libs
Only a few files from the run time library exist. For the time being it consists only of files that are needed at compile time. See the directory rts/adainclude.
Future versions of AVR-Ada should extend the possibilities of the provided RTS. This might include:
Don't count on anything appearing in the near future!