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10.15 Software Setting Preservation
When a device is enumerated, software will configure the device using SET FEATURES and other commands. These
software settings are often preserved across software reset but not necessarily across hardware reset. In Parallel
ATA, only commanded hardware resets can occur, thus legacy software only reprograms settings that are cleared for
the particular type of reset it has issued. In Serial ATA, COMRESET is equivalent to hard reset and a non-commanded
COMRESET may occur if there is an asynchronous loss of signal. Since COMRESET is equivalent to hardware reset,
in the case of an asynchronous loss of signal some software settings may be lost without legacy software knowledge.
In order to avoid losing important software settings without legacy driver knowledge, the software settings
preservation ensures that the value of important software settings is maintained across a COMRESET. Software
settings preservation may be enabled or disabled using SET FEATURES with a subcommand code of 06h. If a device
supports software settings preservation, the feature shall be enabled by default.
10.15.1
COMRESET Preservation Requirements
The software settings that shall be preserved across COMRESET are listed below. The device is only required to
preserve the indicated software setting if it supports the particular feature/command the setting is associated with.
INITIALIZE DEVICE PARAMETERS: Device settings established with the INITIALIZE DEVICE PARAMETERS
command.
Power Management Feature Set Standby Timer: The Standby timer used in the Power Management feature set.
Read/Write Stream Error Log: The Read Stream Error Log and Write Stream Error Logs (accessed using READ
LOG EXT and WRITE LOG EXT).
Security mode state: The security mode state established by Security Feature set commands (see Section 10.5 ).
The device shall not transition to a different security mode state based on a COMRESET. For example, the device
shall not transition from the SEC5: Unlocked / not Frozen state to state SEC4: Security enabled / Locked when a
COMRESET occurs, instead the device shall remain in the SEC5: Unlocked / not Frozen state.
SECURITY FREEZE LOCK: The Frozen mode setting established by the SECURITY FREEZE LOCK command.
SECURITY UNLOCK: The unlock counter that is decremented as part of a failed SECURITY UNLOCK command
attempt.
SET ADDRESS MAX (EXT): The maximum LBA specified in SET ADDRESS MAX or SET ADDRESS MAX EXT.
SET FEATURES (Device Initiated Interface Power Management): The Device Initiated Interface Power
Management enable/disable setting (Word 79, bit 3 of Identify Device) established by the SET FEATURES command
with a Subcommand code of 10h or 90h.
SET FEATURES (Write Cache Enable/Disable): The write cache enable/disable setting established by the SET
FEATURES command with subcommand code of 02h or 82h.
SET FEATURES (Set Transfer Mode): PIO, Multiword, and UDMA transfer mode settings established by the SET
FEATURES command with subcommand code of 03h.
SET FEATURES (Advanced Power Management Enable/Disable): The advanced power management
enable/disable setting established by the SET FEATURES command with subcommand code of 05h or 85h. The
advanced power management level established in the Sector Count register when advanced power management is
enabled (SET FEATURES subcommand code 05h) shall also be preserved.
SET FEATURES (Read Look-Ahead): The read look-ahead enable/disable setting established by the SET
FEATURES command with subcommand code of 55h or AAh.
SET FEATURES (Reverting to Defaults): The reverting to power-on defaults enable/disable setting established by
the SET FEATURES command with a subcommand code of CCh or 66h.
SET MULTIPLE MODE: The block size established with the SET MULTIPLE MODE command.
SANITIZE FREEZE LOCK MODE: The Sanitize Frozen state established by the SANITIZE FREEZE LOCK EXT
command.
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Hard Disk Drive Specification