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Theory of Operation
4.4
Device Presence Detect
The ICH5 SATA host controller provides bits in the PCS register (P0P and P1P) that can be used
by system software to detect the presence of (or lack of) SATA device(s) connected to the SATA
host controller.
Device presence detection has two main benefits:
•
Can potentially assist in quicker boot times (both BIOS POST and operating system) by
eliminating the need for time-consuming device detection algorithms (as required for P-
ATA devices). Limitations to this feature are addressed in the next section.
•
Assists in providing better power management. A port with no device present can be
disabled as a disabled SATA port consumes less power than one that is enabled (See
Section: 4.3.1.1 Port Enabling/Disabling)
4.4.1
Hardware and Software Considerations
The value of the port presence bits is valid only under the following conditions:
•
•
Note: There is no requirement that both ports are enabled when checking the PxP bit; only the port being
examined needs to be enabled.
At some point in time, after a port has been enabled (PCS.PxE== 1), system software will want to
determine two things:
1.
Is a SATA device is attached to the port?
2.
If a SATA device is attached to a port, is it ready to receive commands?
These two items can be determined by software in succession (detect for device, then check
readiness) or simultaneously (check for readiness, as a ready device must be present). Device
detection can be accomplished through an examination of a port's PxP bit (via polling).
However, the amount of time that may elapse between when system software enables a port
and when the ICH5 SATA HBA detects a device (or not) is SATA device specific and is not
specified.
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The SATA host controller is in the D0 power state.
The port to be checked is enabled.
SATA Programmer's Reference Manual
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