Intel 82801EB, Programmer'S Reference Manual

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Theory of Operation
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26 SATA Programmer’s Reference Manual
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:
• The SATA host controller is in the D0 power state.
•
The port to be checked is enabled.
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.