Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
of the non-volatile memory in these devices from AML, PnP IDs exist for each type of extension.
These are PNP0B00, PNP0B01, and PNP0B02. The specific devices that these PnP IDs support are
described in Section 9.15, “PC/AT RTC/CMOS Device”, along with field definition ASL example
code. The drivers corresponding to these device handle operation region accesses to the
SystemCMOS operation region for their respective device types.
All bytes of CMOS that are related to the current time, day, date, month, year and century are readonly.
5.5.2.4.2 PCI Device BAR Target Protocols
This section describes how PCI devices’ control registers can be accessed from ASL. PCI devices
each have an address space associated with them called the Configuration Space. At offset 0x10
through offset 0x27, there are as many as six Base Address Registers, (BARs). These BARs contain
the base address of a series of control registers (in I/O or Memory space) for the PCI device. Since a
Plug and Play OS may change the values of these BARs at any time, ASL cannot read and write
from these deterministically using I/O or Memory operation regions. Furthermore, a Plug and Play
OS will automatically assign ownership of the I/O and Memory regions associated with these BARs
to a device driver associated with the PCI device. An ACPI OS (which must also be a Plug and Play
operating system) will not allow ASL to read and write regions that are owned by native device
drivers.
If a platform uses a PCI BAR Target operation region, an ACPI OS will not load a native device
driver for the associated PCI function. For example, if any of the BARs in a PCI function are
associated with a PCI BAR Target operation region, then the OS will assume that the PCI function is
to be entirely under the control of the ACPI system firmware. No driver will be loaded. Thus, a PCI
function can be used as a platform controller for some task (hot-plug PCI, and so on) that the ACPI
system firmware performs.
5.5.2.4.2.1 Declaring a PCI BAR Target Operation Region
PCI BARs contain the base address of an I/O or Memory region that a PCI device’s control registers
lie within. Each BAR implements a protocol for determining whether those control registers are
within I/O or Memory space and how much address space the PCI device decodes. (See the PCI
Specification for more details.)
PCI BAR Target operation regions are declared by providing the offset of the BAR within the PCI
device’s PCI configuration space. The BAR determines whether the actual access to the device
occurs through an I/O or Memory cycle, not by the declaration of the operation region. The length of
the region is similarly implied.
In the term OperationRegion(PBAR, PciBarTarget, 0x10, 0x4), the offset is the offset of the
BAR within the configuration space of the device. This would be an example of an operation region
that uses the first BAR in the device.
5.5.2.4.2.2 PCI Header Types and PCI BAR Target Operation Regions
PCI BAR Target operation regions may only be declared in the scope of PCI devices that have a PCI
Header Type of 0. PCI devices with other header types are bridges. The control of PCI bridges is
beyond the scope of ASL.
222 April, 2015 Version 6.0