You could also use command-line utilities for a robot-arm driver. The driver could register the name, /dev/robot/arm/angle, and any writes to this device are interpreted as the angle to set the robot arm to. To test the driver from the command line, you'd type:
echo 87 >/dev/robot/arm/angle
The echo utility opens /dev/robot/arm/angle and writes the string ("87") to it. The driver handles the write by setting the robot arm to 87 degrees. Note that this was accomplished without writing a special tester program.
Another example would be names such as /dev/robot/registers/r1, r2, ... Reading from these names returns the contents of the corresponding registers; writing to these names set the corresponding registers to the given values.
Even if all of your other IPC is done via some non-POSIX API, it's still worth having one thread written as a resource manager for responding to reads and writes for doing things as shown above.