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Theory of Operation
4.3.1.1
Port Enabling/Disabling
By default, the SATA ports are set (by hardware) to the disabled state as a result of a D3 to D0
power state transition (due to initial power-on reset or resume from suspend).
System software may choose to (keep) disable a port as a result of a device being disconnected
from a port(s). Overall power consumption can be reduced if system software only enables those
ports that have SATA devices attached. This is especially beneficial to mobile systems.
The following are general guidelines to be used for determining when the SATA ports shall be
enabled and when they should be disabled:
Note: IMPORTANT – A port shall not be enabled if power is not applied to the attached SATA device.
Power shall be applied to the device for a period of at least 30ms before its associated port is to be
enabled by system software. System software shall insure that a port is disabled prior to removing
power to the associated SATA device.
• A port on the ICH5 SATA host controller shall be enabled in order for the PCS.PxP (where x
is 0 for Port 0 or 1 for Port 1) bits to be accurate. See Section 4.4.1 Hardware and Software
Considerations.
• As part of a robust power conservation strategy, a port on the ICH5 SATA host controller
should be disabled when a SATA device is not physically present or is unusable.
Ports may be enabled and disabled via the following methods:
• Operating system device driver (either directly or through ACPI)
• ACPI power management control method (e.g., _PSx)
4.3.1.1.1
BIOS Considerations
To insure that SATA devices are functional following certain system power state transitions,
system BIOS shall enable the SATA ports under the following conditions:
• Any APM supported system state transition where the ICH5 SATA host controller is reset.
• Device power state transitions where the operating system cannot enable the SATA ports
through the use of a native (non-ICH5 SATA host controller aware) device driver or through
the use of ACPI control methods.
These considerations do not apply if both of the following conditions are true:
• The SATA devices are not crucial to operating system boot or for resuming from hibernation
• The operating system implements an ICH5 SATA host controller aware device driver.
Failure by the system BIOS to provide the required support will result in device inaccessibility
and/or loss of operating system functionality.
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SATA Programmer's Reference Manual
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