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14 CONSTELLATION ES.2 SERIAL ATA PRODUCT MANUAL, REV. H
2.8.4.1 Extended Power Conditions - PowerChoice
TM
Utilizing the load/unload architecture a programmable power management interface is provided to tailor systems 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 savings 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" sub-
command to enter any supported power condition. Legacy power commands Standby Immediate and Idle Immediate also
provide a method to directly transition the drive into supported power conditions.
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
S.M.A.R.T. Read Data Reports
• Attribute 192 - Emergency Retract Count
• Attribute 193 - Load/Unload Cycle Count
PowerChoice Manufacture Default Power Condition Timer Values
Default power condition timer values have been established to assure product reliability and data integrity. A minimum timer value
threshold of two minutes ensures the appropriate amount of background drive maintenance activities occur. Attempting to set a timer
values less than the specified minimum timer value threshold will result in an aborted EPC "Set Power Condition Timer" subcommand.
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)