DEVSLP (Device Sleep) was added in revision 3.2 of the SATA specification published by the SATA-IO.
Here you can find out about this new feature and the changes required to make it work.
What is DEVSLP and why do we need it?
DEVSLP is a signal that is sent to a SATA disk drive to tell it to enter a very low power state. The SATA specification has always allowed for the drive to enter a low power state, but in the past, the drive had to keep its high-speed transceiver circuitry powered up in order to receive the signal to wake up again. DEVSLP removes this power hungry requirement by using a separate low-speed pin.
The ability to enter an ultra-low power state is crucial for ultrabooks and other battery powered devices. Using DEVSLP, manufacturers are able to produce devices with power consumption of microWatts compared to milliWatts in previous generation drives.
Where did they find the extra pin?
There were no spare pins in the SATA connector standard for 2.5″ and 3.5″ drives (SFF-8482). Revision 3.2 assigns pin P3 as DEVSLP. Pins P1, P2 and P3 used to be a 3.3V power supply to the drive; very few drives (if any) and very few systems ever implemented 3.3V power so the pins were re-designated. If you should happen to put a DEVSLP enabled drive in a system that provides 3.3V power, the drive will go into low power mode and stay there.
Anything else I need to know?
DEVSLP is intended to use an open drain driver on the host system.