Advanced Configuration and Power Interface Specification

ACPI-Defined Devices and Device-Specific Objects
Note: This means that the CENTURY field in the Fixed ACPI Description Table may only contain values
between 0 and 63.
Example:
This is an example of how this device could be described:
Device (RTC0) {
Name(_HID, EISAID("PNP0B00"))
Name (_FIX, Package(1) {
EISAID("PNP0B00") }
)
Name(_CRS, ResourceTemplate() {
IO(Decode16, 0x70, 0x70, 0x1, 0x2)
}
OperationRegion(CMS1, SystemCMOS, 0, 0x40)
Field(CMS1, ByteAcc, NoLock, Preserve) {
AccessAs(ByteAcc, 0),
CM00, 8,
,256,
CM01, 8,
CM02, 16,
, 216,
CM03, 8
}
9.15.2Intel PIIX4-compatible RTC/CMOS Devices (PNP0B01)
The Intel PIIX4 contains an RTC/CMOS device that is compatible with the one in the PC/AT. But it
contains 256 bytes of non-volatile RAM. The first 64 bytes are accessed via the same mechanism as
the 64 bytes in the PC/AT. The upper 192 bytes are accessed through an interface that is only used
on Intel chips. (See 82371AB PCI-TO-ISA / IDEXCELERATOR (PIIX4) for details.)
Any platform containing this device or one that is compatible with it may use the PNP ID PNP0B01.
This will allow an ACPI-compatible OS to recognize the RTC/CMOS device as using the
programming interface of the PIIX4. Thus, the array of bytes that ASL can read and write with this
device is 256 bytes long.
Note: This also means that the CENTURY field in the Fixed ACPI Description Table may contain values
between 0 and 255.
Example:
This is an example of how this device could be described:
Version 6.0 535