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Constellation ES.2 Serial ATA Product Manual, Rev. D 13
3.8.4.1 Extended Power Conditions - PowerChoice
TM
Utilizing the load/unload architecture a programmable power management interface is provided to tailor sys-
tems for reduced power consumption and performance requirements.
The table below lists the supported power conditions available in PowerChoice. Power conditions are ordered
from highest power consumption (and shortest recovery time) to lowest power consumption (and longest
recovery time) as follows: Idle_a power >= Idle_b power >= Idle_c power >= Standby_z power. The further you
go down in the table, the more power savings is actualized. For example, Idle_b results in greater power sav-
ings than the Idle_a power condition. Standby results in the greatest power savings.
Each power condition has a set of current, saved and default settings. Default settings are not modifiable.
Default and saved settings persist across power-on resets. The current settings do not persist across power-on
resets. At the time of manufacture, the default, saved and current settings are in the Power Conditions log
match.
PowerChoice is invoked using one of two methods
• Automatic power transitions which are triggered by expiration of individual power condition timers. These
timer values may be customized and enabled using the Extended Power Conditions (EPC) feature set using
the standardized Set Features command interface.
• Immediate host commanded power transitions may be initiated using an EPC Set Features "Go to Power
Condition" subcommand to enter any supported power condition. Legacy power commands Standby Imme
-
diate and Idle Immediate also provide a method to directly transition the drive into supported power condi-
tions.
PowerChoice exits power saving states under the following conditions
• Any command which requires the drive to enter the PM0: Active state (media access)
• Power on reset
PowerChoice provides the following reporting methods for tracking purposes
Check Power Mode Command
• Reports the current power state of the drive
Identify Device Command
• EPC Feature set supported flag
• EPC Feature enabled flag is set if at least one Idle power condition timer is enabled
Power Condition Log reports the following for each power condition
• Nominal recovery time from the power condition to active
• If the power condition is Supported, Changeable, and Savable
• Default enabled state, and timer value
• Saved enabled state, and timer value
• Current enabled state, and timer value
Power Condition Name Power Condition ID Description
Idle_a 81
H
Reduced electronics
Idle_b 82
H
Heads unloaded. Disks spinning at full RPM
Idle_c 83
H
Heads unloaded. Disks spinning at reduced RPM
Standby_z 00
H
Heads unloaded. Motor stopped (disks not spinning)