Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
A _UID object evaluates to either a numeric value or a string.
Arguments:
None
Return Value:
An Integer or String containing the Unique ID
6.2 Device Configuration Objects
This section describes objects that provide OSPM with device specific information and allow OSPM
to configure device operation and resource utilization.
OSPM uses device configuration objects to configure hardware resources for devices enumerated
via ACPI. Device configuration objects provide information about current and possible resource
requirements, the relationship between shared resources, and methods for configuring hardware
resources.
Note: these objects must only be provided for devices that cannot be configured by any other hardware
standard such as PCI, PCMCIA, and so on.
When OSPM enumerates a device, it calls _PRS to determine the resource requirements of the
device. It may also call _CRS to find the current resource settings for the device. Using this
information, the Plug and Play system determines what resources the device should consume and
sets those resources by calling the device’s _SRS control method.
In ACPI, devices can consume resources (for example, legacy keyboards), provide resources (for
example, a proprietary PCI bridge), or do both. Unless otherwise specified, resources for a device
are assumed to be taken from the nearest matching resource above the device in the device
hierarchy.
Some resources, however, may be shared amongst several devices. To describe this, devices that
share a resource (resource consumers) must use the extended resource descriptors (0x7-0xA)
described in Section 6.4.3, “Large Resource Data Type.” These descriptors point to a single device
object (resource producer) that claims the shared resource in its _PRS. This allows OSPM to clearly
understand the resource dependencies in the system and move all related devices together if it needs
to change resources. Furthermore, it allows OSPM to allocate resources only to resource producers
when devices that consume that resource appear.
The device configuration objects are listed in Table 6-171
Table 6-171 Device Configuration Objects
Object
_CDM
_CRS
_DIS
_DMA
_DSD
Description
Object that specifies a clock domain for a processor.
Object that specifies a device’s current resource settings, or a control method that generates
such an object.
Control method that disables a device.
Object that specifies a device’s current resources for DMA transactions.
Object that evaluates to device specific information
294 April, 2015 Version 6.0