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6.1 Reset and Diagnosis
C141-E239 6-5
6.1.2.1 Software settings 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 reservation 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 (refer to Section 5.3.2 (28)). If a device supports
software settings preservation, the feature shall be enabled by default.
6.1.2.2 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.
• Security mode state
The security mode state established by Security Mode feature set commands
(refer to Section 6.13 of the ATA/6 specification). 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.