Reporting Host Power Management Events to SMC

The Host Bridge may also need to report power management messages to the System Management Controller residing on the HT bus (e.g. within the South bridge). The mechanism for reporting such events is the STOP_GRANT message. Like the STPCLK message, the SMAF field defines the type of event being reported and the action required.

Processor VID/FID

The specification defines a STOP_GRANT message for Voltage ID and Frequency ID changes associated with the processor. The Athlon processors support changing the frequency and voltage used by the processor as a means of power conservation. That is, if the processor clock frequency is slowed, the voltage may also be lowered for greater power conservation. When the host initiates a VID/FID change, this indicates that the system is entering a low-power state. Consequently, the north bridge must generate a STOP_GRANT message with an SMAF code specifying the VID/FID change. This message results in the assertion of LDTSTOP#.