power is applied.
Backplane Hot Plug Connector
Figure 21-2 illustrates the contact points of a backplane-based Hot Plug connec- tor. Notice that the illustration shows the standard short and long contacts at the device connector and two long contacts at the host receptacle. The layout of con- tacts provide three mating points as a drive is plugged or unplugged from the backplane receptacle. Please also see Table 21-2.
Figure 21-1: Pin Lengths and Mating for Cable Hot Plug Connection
Table 21-1: Contact Mating When Drive is Plugged into Receptacle
Contact Combinations
Mating
Points Contact Assignments
Long to Short First 3.3vdc Precharge Contact 5vdc Precharge Contact 12vdc Precharge Contact All ground Contacts Short to Short Second Other 3.3vdc Contacts (2)
Other 5vdc Contacts (2) Other 12vdc Contacts (2)
Device Activity/Staggered Spinup disable Differential Signal Pairs (4 contacts)
SATA Storage Technology
Drive Plug/Unplug Detection
The ability to detect the insertion or removal of a drive can be implemented by a Hot Plug compatible host or PM device port interface. Figure 21-3 illustrates an example circuit for detecting drive attachment and removal, which is provided by the specification.
Figure 21-2: Pin Lengths and Mating for Backplane Hot Plug Connections
Table 21-2: Contact Mating When Drive is Plugged into Receptacle
Contact Combinations
Mating
Points Contact Assignments
Long to Long First Two Ground Contacts Long to Short Second 3.3vdc Precharge Contact
5vdc Precharge Contact 12vdc Precharge Contact All Other Ground Contacts (6) Short to Short Third Other 3.3vdc Contacts (2)
Other 5vdc Contacts (2) Other 12vdc Contacts (2)
Device Activity/Staggered Spinup disable Differential Signal Pairs (4 contacts)
Chapter 21: Hot Plug
To support hot insertion and removal, the specification requires that SATA devices bus the power contacts together for each supply voltage as is illustrated in Figure 21-3. The contact assignments are:• P1, P2, and P3 -- 3.3V power contacts • P7, P8, and P9 -- 5V power contacts • P13, P14, and P15 -- 12V power contacts
When device attachment or removal is detected, the host interface sets the “X” bit in the SError register’s DIAG field (Figure 21-4).
22
Link Power
Management
Previous Chapter
The SATA specifications add several key features intended to enable hot plug- gable drives. These features include a Hot Plug connector definition, detection of drive insertion and removal, and asynchronous signal recovery. The previous chapter discussed these and other features that support a Hot Plug solution.
This Chapter
SATA defines two levels of power conservation for the link, called Slumber and Partial. This chapter describes the protocol associated with transitioning the link into a low power state and recovering back to normal power and operation.
The Next Chapter
A variety of features built into the SATA subsystem assist in diagnosing prob- lems, ensuring compliance, and validating proper operation of the SATA inter- face. The next chapter discusses these Built In Self Tests (BIST) some of which are required, while others are optional.
Overview
Like other serial interfaces based on 8b/10b encoding, SATA Phys are normally in the Phy Rdy state and are continuously sending and receiving information to keep the interface in the communicating state. Even during long periods of disk inactivity the SATA interface continues to send SYNC primitives (logical idle) to keep the interface ready to handle commands with very little latency when they are issued. Of course, the downside to this approach is that power continues to be consumed even when no work is being performed. The SATA specification defines an optional mechanism for placing the interface into the electrical idle state to conserve power and back into the normal operating state.
SATA Storage Technology
SATA defines two levels of link power conservation where the Phy is powered, but is dissipating less power than when in the PhyRdy state.
• Partial — Link power consumption is reduced by some vendor-specific level and the exit latency back to the PhyRdy state must be 10µs or less. • Slumber — Link power consumption is reduced by some vendor-specific
level less than that of the Partial state, and the exit latency from this state must be no longer than 10ms. As in the Partial state a zero differential volt- age must be maintained unless a transmitter is AC coupled.
Even though the specification does not define a specific amount of power sav- ings, the vendor may (the spec. says “should”) publish the “not to exceed” power when in the Partial and Slumber states.
Configuring Link Power Management
Because link power management is an optional feature, the host implementa- tion may or may support power management and the same is true of the drive. Whether a SATA host system supports link power management will likely depend on the operation environment; the two extremes being, battery-pow- ered notebook computers where power saving is crucial and server-based plat- forms where the emphasis in on non-stop operation and low-latency disc access.
Detecting/Enabling Drive Link Power Management
Whether a drive supports the Partial or Slumber states is reported in the Iden- tify Drive data. A drive may support:
• receipt of Host-initiated commands to enter Link Power Management • initiation of commands that place the link into the partial or slumber states Table 22-1 on page 385 lists the Identify Data information related to link power management, including its Link Power Management capabilities and whether these features are enabled.
Drives that report they can receive requests to enter the Partial or Slumber states are enabled to do so by default. However, drives that report the ability to ini- tiate entry into a low-power link state are disabled to do so by default. Software must enable this feature via the SetConfiguration command.