The project is aimed to port GNAT GPL for LEGO MINDSTROMS NXT-Ravenscar edition to Raspberry Pi. The work includes the porting of GNAT compiler toolset, Ravenscar runtime and drivers. The GNAT compiler toolset in GNAT GPL for LEGO MINDSTROMS NXT-Ravenscar edition can be used directly for Raspberry Pi. Only the porting of Ravenscar runtime and drivers are necessary. They are placed in folers RTS/drivers and RTS/ravenscar respectively. Application level test programs resides in RTS-test folder. 
To compile example programs on Windows platform, in my case, a laptop with Windows 7 64bit home basic pre-installed, first download GNAT GPL for LEGO MINDSTROMS NXT-Ravenscar edition from Libre.Adacore.com. Download also gnumake executable and place it into the bin folder in GNAT installation. Download all the files in both RTS and RTS-Test folders. Open a console and change current directory to say RTS-Test/blinker and invoke 'make'. Blinker01.bin as well as other stuffs will be created. Copy Blinker01.bin to a SD card as kernel.img, together with other stuffs needed for booting Pi. One can also tranfer Blinker01.bin directly to Pi using a bootloader. Please visit https://github/dwelch67/raspberrypi for detailed instruction.
At present stage, only drivers for GPIO, mini_uart, sound playing by PWM and a  system timer are prepared, other drivers will come soon.