OldMicroGuy:
PRR is the power reduction register. The larger MCUs have more peripherals and one register isn't enough, so they have PRR0 and PRR1 instead of just PRR.
Thanks Jack that explains why the Narcoleptic library doesn't work.
Can anyone recommend a sleep library for the ATmega1284P?
Roger
What sort of sleeping do you want to do? Narcoleptic has a wide range of capabilities, sleep as well as power reduction while running.