Thread: How Windows Determines ACPI Compatibility

SUMMARY:

This article explains the procedure used by Windows to allow and install Advanced Configuration and Power Interface (ACPI) functionality.

MORE INFORMATION

The Txtsetup.sif File

The Txtsetup.sif files have information used for device discovery and installation during text-mode Setup. If an entry is not creating for a device in this file, the device is not installed during the text-mode Setup part of a Windows installation.

There are three sections in the Txtsetup.sif file to offer for ACPI detection and installation:
• [ACPIOptions]
• [GoodACPIBios]

ACPI Configuration in the BIOS

ACPI systems consist of a series of ten tables. These ten tables define which devices are present on the system and what their ability as they share to configuration and power management. These tables are built by the system BIOS during startup. When the system starts, look for specific items in these two tables to find out whether the system is ACPI compliant. This information is extracted from these tables in the form of an OEM ID, OEM Table ID, OEM REVISION, REVISION and Creator. If these tables are not there or the information in the above descriptors is invalid, the system is implicit that non-ACPI and legacy Hardware Abstraction Layer (HAL) is installed.

A sample of the Fixed ACPI Description table might be:
OEM ID = "COMPAQ"
OEM Table ID = "FACPTBL"
OEM Revision = "432"
Creator Revision = "1"

A sample of the Root System Description table for this entry would be:
OEM Table ID = "CPQB01B"

The information found in these tables is contrast to the entries establish in the Txtsetup.sif file. The following assumptions are prepared and actions performed based on this information:

*If the system BIOS is on the bad BIOS list, the ACPI HAL is not installed. If the BIOS is not on the bad BIOS list, and the date of the BIOS is later than 1/1/99, it is assumed to be a good BIOS and the ACPI HAL is applied. If the date is earlier than 1/1/99, the table information is checked against the good BIOS list. If the BIOS is present, the ACPI HAL is installed.

A BIOS shows on the bad BIOS list because it is recognized to cause system instability if the ACPI HAL is used. This instability can range in severity from hardware not acting properly to system hangs and data loss. For this cause it is never a good idea to override the statements made by this list. This also applies to systems that are not detected as ACPI compliant. If the table header information is wrong, it can be assumed that the device configuration information contained in these tables is equally questionable. must you encounter any of the instabilities linked with overriding the default ACPI settings, Microsoft cannot help you in any manner short of a complete reinstallation of the operating system. An upgrade installation cannot fix the damage done by a bad or incomplete ACPI BIOS. Nonetheless, should you need to override these settings, you can do so using the following information:

Two entries named ACPIEnable and ACPIBiosDate show in the [ACPIOptions] section. The ACPIBiosDate entry supplies the date once which a BIOS is considered good. The default setting for this entry is 1/1/1999. The ACPIBiosDate entry is of little use in forcing an ACPI installation. The three feasible values for the ACPIEnable entry find out the ACPI detection and installation behavior:

• 0: ACPI is disabled at installation regardless of the system BIOS
• 1: ACPI is enabled at installation if an ACPI BIOS is present
• 2: ACPI is enabled based on the GoodACPIBios list and ACPIBiosDate
The default setting is 2.

To override the default and force an ACPI installation, edit the Txtsetup.sif file placed on Setup disk 1 and modify the ACPIEnable value to 1. Save the file and then restart the installation.
ACPI does need the presence of some new hardware such as an SMBus or I2c -compatible bus and other items, the absence of which can stop the system from being ACPI capable.