System State-to-Device State Mappings (SxD)
Updated: June 9, 1999
File name: ACPI_SxD.rtf
About This Download
DRAFT Version 0.7 February 19, 1999
This download draft white paper describes the algorithms the ACPI driver provided with the Microsoft Windows 2000 operating system uses to calculate the state mappings associated with a system and its devices transitioning from the working state to a sleeping state. The S-state-to-D-state mappings show how _SxD objects can be used to eliminate ambiguity and to provide rules and recommendations to system/BIOS developers to ensure a system will function as designed.
When a system transitions from the working state (S0) to a sleeping state (S1-S4), all the devices in the system must transition to the appropriate device state (D0-D3). The system state-to-device state mappings for the individual devices and buses in the system are calculated by the Windows 2000 ACPI driver during initialization.
These mappings are used and propagated throughout the system to allow devices to transition into the appropriate state whenever enabled, so that they will wake the computer. The S-state-to-D-state mappings at best can be cumbersome to calculate. Sometimes they are impossible to calculate accurately. To address this problem, the _SxD objects were created. These objects allow the ACPI driver to generate an explicit S-state-to-D-state mapping for any given sleeping state (represented by "x"), and help to eliminate erratic system behavior.
The goal of this download draft white paper is to document the algorithms the Windows 2000 ACPI driver uses to calculate the S-state-to-D-state mappings, show how the _SxD objects can be used to eliminate ambiguity, and provide rules and recommendations to system/BIOS developers to ensure their systems work as designed This white paper requires a working knowledge of the current PCI Specification and the PCI Bus Power Management Interface Specification. Both of these specifications can be obtained from the PCI Special Interest Group home page at: http://www.pcisig.com/ specifications/ .