Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
}
}
//
// Second function identifier
//
case(ToUUID(“107ededd-d381-4fd7-8da9-08e9a6c79644”))
{
//
// Function 0: Return supported functions (there is only one revision)
//
if (LEqual(Arg2,Zero))
return (Buffer() {0x3}) // only one function supported
//
// Function 1
//
if (LEqual(Arg2,One))
{
… function 1 code …
Return(Unicode(“text”))
}
//
// Function 2+: Runtime Error
//
else
BreakPoint;
}
}
//
// If not one of the UUIDs we recognize, then return a buffer
// with bit 0 set to 0 indicating no functions supported.
//
return(Buffer(){0})
9.15 PC/AT RTC/CMOS Devices
Most computers contain an RTC device which also contains battery-backed RAM represented as a
linear array of bytes. There is a standard mechanism for accessing the first 64 bytes of non-volatile
RAM in devices that are compatible with the Motorola RTC/CMOS device that was in the IBM PC/
AT. Newer devices usually contain at least 128 bytes of battery-backed RAM. New PNP IDs were
assigned for these devices.
Certain bytes within the battery-backed RAM have pre-defined values. In particular, the time, date,
month, year, century, alarm time and RTC periodic interrupt are read-only.
9.15.1 PC/AT-compatible RTC/CMOS Devices (PNP0B00)
The standard PC/AT-compatible RTC/CMOS device is denoted by the PnP ID PNP0B00. If an
ACPI platform uses a device that is compatible with this device, it may describe this in its ACPI
namespace. ASL may then read and write this as a linear 64-byte array. If PNP0B00 is used, ASL
and ACPI operating systems may not assume that any extensions to the CMOS exist.
534 April, 2015 Version 6.0