Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
8.4.4.4.1 Example
The following ASL describes a system that uses _RDI to describe the dependencies between three
power resources and system level power states:
PowerResource(PWRA,0,0) {
Method(_ON) {…}
Method(_OFF) {…}
Method(_STA) {…}
}
PowerResource(PWRB,0,0) {
Method(_ON) {…}
Method(_OFF) {…}
Method(_STA) {…}
}
PowerResource(PWRC,0,0) {}
// power rail local to DEVA
// active power resource (_OFF turns rail off)
// power rail shared between DEVB and the processor
// active power resource (_OFF drives platform vote)
// clock rail shared between DEVC and the processor
// passive power resource
Device (DEVA) {
Name(_PR0,Package(){PWRA})
}
Device (DEVB) {
Name(_PR0,Package(){PWRB})
}
Device (DEVC) {
Name(_PR0,Package(){PWRC})
}
Device (SYM) {
Name(_RDI,
Package() {
0, // Revision
Package(){}
// Local State 1 has no power resource
// dependencies
Package(){PWRA}
// Local State 2 cannot be entered if DEVA
// is in D0 due to PWRA
Package(){PWRA, PWRB, PWRC} // Local State 3 cannot be
entered if
…
})
// DEVA is in D0 (due to PWRA), DEVB is in
// D0 (due to PWRB) or DEVC is in D0 (due to
// PWRC)
OSPM will turn the traditional power resource (PWRA) ON or OFF by waiting for the reference
count to reach 0 (meaning DEVA has left D0) and running the _OFF method. Similarly, PWRB is
turned ON or OFF based on the state of DEVB. Note that because the CPUs require the shared
power rail to be ON while they are running, PWRB’s _ON and _OFF drive a vote rather than the
physical HW controls for the power rail. In this case, _STA reflects the status of the vote rather than
the physical state of PWRB.
OSPM guarantees ordering between PWRA/PWRB’s _ON and _OFF transitions and DEVA/
DEVB’s D-state transitions. That is, PWRA can only be turned OFF after DEVA has left D0, and
must be turned ON before transitioning DEVA to D0. However, the OS requirements for ordering
460 April, 2015 Version 6.0