"Smart Reduced Power Consumption Techniques" [0] are supported by AT86RF233, ATmega2564/1284/644RFR2 and ATmega256/128/64RFR2 devices. Functionality is the same as on AT86RF233, so we can just enable it. [0] http://ww1.microchip.com/downloads/en/Appnotes/Atmel-42356-Smart-Reduced-Power-Consumption-Techniques_ApplicationNote_AT02594.pdf