From the 777Mel regarding an inop autothrottle-
1.) Autothrottle commands are provided by the Thrust Management Computing Function (TMCF). TMCF also provides EICAS indications of EPR reference values, thrust mode, and selected temperature.
In some failure modes of the autothrottle system, these EICAS indications will also be inoperative.
2.) The flight must remain within 180 minutes of landing at a suitable airport.