I have succeeded in porting GNAT GPL for MINDSTORMS NXT-Ravenscar edition to Raspberry Pi. If anyone is interested in programing in Ada, this port will provide an Ada-only environment on a bare board Raspberry Pi. One can exercise realtime multitask programming like cyclic task, sporadic task as well as protected accessing of shared resources with fixed-priority pre-emptive scheduling scheme. Please visit
https://github.com/zhenggennj/GNAT4Rpi.