Advanced Configuration and Power Interface Specification Hewlett-Packard Corporation
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- Navigate this page:
- Table B-1 Video Extension Object Requirements
- B.2 Definitions Built-in display adapter
- Display device
- B.4 Display-specific Methods
- B.4.1 _DOS (Enable/Disable Output Switching)
- Integer
- B.4.2 _DOD (Enumerate All Devices Attached to the Display Adapter)
- Non-video output devices
- Package
- Table B-2: Video Output Device Attributes
- Figure B-1 Example Display Architecture Table B-3: Example Device Ids
APPENDIX B: Video ExtensionsB ACPI Extensions for Display Adapters B.1 Introduction This section of the document describes a number of specialized ACPI methods to support motherboard graphics devices. In many cases, system manufacturers need to add special support to handle multiple output devices such as panels and TV-out capabilities, as well as special power management features. This is particularly true for notebook manufacturers. The methods described here have been designed to enable interaction between the system BIOS, video driver, and OS to smoothly support these features. Systems containing a built-in display adapter are required to implement the ACPI Extensions for Display Adapters. Table B-1 Video Extension Object Requirements
B.2 Definitions
B.3 ACPI Namespace This is an example of the display-related namespace on an ACPI system: GPE // ACPI General-purpose HW event _L0x // Notify(VGA, 0x80) to tell OSPM of the event, when user presses // the hot key to switch the output status of the monitor. // Notify(VGA, 0x81) to tell the event to OSPM, when there are any // changes on the sub-devices for the VGA controller
|- PCI
|- VGA // Define the VGA controller in the namespace |- _PS0 / PR0 |- _PS1 / PR1 |- _PS3
|- _DOS // Method to control display output switching |- _DOD // Method to retrieve information about child output devices |- _ROM // Method to retrieve the ROM image for this device |- _GPD // Method for determining which VGA device will post |- _SPD // Method for controlling which VGA device will post |- _VPO // Method for determining the post options |- CRT // Child device CRT |- _ADR // Hardware ID for this device |- _DDC // Get EDID information from the monitor device |- _DCS // Get current hardware status |- _DGS // Query desired hardware active \ inactive state |- _DSS // Set hardware active \ inactive state |- _PS0 \ |- _PS1 - Power methods |- _PS2 - for the output device |- _PS3 / |- LCD // Child device LCD |- _ADR // Hardware ID for this device |- _DDC // Get EDID information from the monitor device |- _DCS // Get current hardware status |- _DGS // Query desired hardware active \ inactive state |- _DSS // Set hardware active \ inactive state |- _BCL // Brightness control levels |- _BCM // Brightness control method |- _BQC // Brightness Query Current Level |- _PS0 \ |- _PS1 - Power methods |- _PS2 - for the output device |- _PS3 / |- TV // Child Device TV |- _ADR // Hardware ID for this device |- _DDC // Get EDID information from the monitor device |- _DCS // Get current hardware status |- _DGS // Query desired hardware active \ inactive state |- _DSS // Set hardware active \ inactive state The LCD device represents the built-in output device. Mobile PCs will always have a built-in LCD display, but desktop systems that have a built-in graphics adapter generally don’t have a built-in output device. B.4 Display-specific Methods The methods described in this section are all associated with specific display devices. This device-specific association is represented in the namespace example in the previous section by the positioning of these methods in a device tree. B.4.1 _DOS (Enable/Disable Output Switching) Many ACPI machines currently reprogram the active display output automatically when the user presses the display toggle switch on the keyboard. This is done because most video device drivers are currently not capable of being notified synchronously of such state changes. However, this behavior violates the ACPI specification, because the system modifies some graphics device registers. The existence of the _DOS method indicates that the system BIOS is capable of automatically switching the active display output or controlling the brightness of the LCD. If it exists at all, the _DOS method must be present for all display output devices. This method is required if the system supports display switching or LCD brightness control. Arguments: (1) Arg0 – An Integer containing the encoded switching controls (see below) Return Value: None
Additional Argument Information: Bits 1:0
0 – The system BIOS should not automatically switch (toggle) the active display output, but instead just save the desired state change for the display output devices in variables associated with each display output, and generate the display switch event. OSPM can query these state changes by calling the _DGS method. 1 – The system BIOS should automatically switch (toggle) the active display output, with no interaction required on the OS part. The display switch event should not be generated in this case. 2 – The _DGS values should be locked. It’s highly recommended that the system BIOS do nothing when hotkey pressed. No switch, no notification. 3 – The system BIOS should not automatically switch (toggle) the active display output, but instead generate the display switch event notify codes 0x82, 0x83, or 0x84. OSPM will determine what display output state should be set, and change the display output state without further involvement from the system BIOS. Bit 2 0 – The system BIOS should automatically control the brightness level of the LCD when the power changes from AC to DC. 1 – The system BIOS should not automatically control the brightness level of the LCD when the power changes from AC to DC. The _DOS method controls this automatic switching behavior. This method should do so by saving the parameter passed to this method in a global variable somewhere in the BIOS data segment. The system BIOS then checks the value of this variable when doing display switching. This method is also used to control the generation of the display switching Notify(VGA, 0x80/0x81). The system BIOS, when doing switching of the active display, must verify the state of the variable set by the _DOS method. The default value of this variable must be 1.
B.4.2 _DOD (Enumerate All Devices Attached to the Display Adapter) This method is used to enumerate devices attached to the display adapter. This method is required if integrated controller supports output switching. On many laptops today, a number of devices can be connected to the graphics adapter in the machine. These devices are on the motherboard and generally are not directly enumerable by the video driver; for this reason, all motherboard VGA attached devices are listed in the ACPI namespace. These devices fall into two categories:
Both ACPI and the video driver have the ability to program and configure output devices. This means that both ACPI and the video driver must enumerate the devices using the same IDs. To solve this problem, the _DOD method returns a list of devices attached to the graphics adapter, along with device-specific configuration information. This information will allow the cooperation between ACPI components and the video driver. Every child device enumerated in the ACPI namespace under the graphics adapter must be specified in this list of devices. Each display device must have its own ID, which is unique with respect to any other attachable devices enumerated. Arguments: None
Return Value: A Package containing a variable-length list of Integers, each of which contains the 32-bit device attribute of a child device (See table B-2) Example: Method (_DOD, 0) { Return (
Package() { 0x00000110, // Primary LCD panel, not detectable by BIOS 0x80000100, // CRT type display, not detectable by BIOS 0x80000220, // TV type display, not detectable by the BIOS 0x80000411, // Secondary LCD panel, not detectable by BIOS } ) } Table B-2: Video Output Device Attributes
As mentioned in the above table, a “Pipe” or “Head” refers to a unique display content stream e.g. at a particular color-depth, resolution, and refresh-rate. The “Port” refers to the display output device attachment and may include a DAC, encoder or other mechanism required to support a given display end-point. The “Display Type” describes the generalized class of display output technology, and the means of integration. The “Display Index” is then an index that assists in creating a unique identifier display end-points in scenarios where other attributes are the same. 
Figure B-1 Example Display Architecture Table B-3: Example Device Ids
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