SAARU is your answer......will give ATT info. When you electrically power up a dead 777 this is what you get. The aircraft goes thru a series of power up checks which take about 6 minutes and has noticeable cockpit effects, then is fully powered ( like in the supplied picture -link )
Switching on the ADIRU and inputting a valid Lat / Long position will then give you the rest ATT/ Hdg /Pos . ( after a further 11 minutes )