[anthonj]

Nasa CFS, is written is plain C (trying to follow MISRA C, etc). It's open on girhub abd used by many companies. It's typically run over freertos or RTEMS, not sure here.

Personally I find the project extremely messy, and kinda hate working with it.

[sheepybloke]

It's most likely using vxworks for it's OS, since I believe it's one of the only fully certified ARINC653 OS's for human flight. It's used in most Aircraft and space missions.

[__d]

Yeah, that was my guess too but the comment about separate implementation for the backup system made me wonder if there was a different OS, and the which was running where.