Reporting Power Management Events to the Host Bridge

HT provides two System Management messages that can be used to report power management events to the host.

• STPCLK message ” uses the SMAF field to define the type of event being reported and the action to be taken. The SMAF field encoding is not defined by the HT specification.

• SMI message ” used to notify (interrupt) the processor when a system management event occurs. The SMI message can support power management as will as other features. (Note: SMI is an x86 legacy signal and is discussed in more detail in "X86 CPU Compatibility" on page 491.)

Message transmission may be stimulated by either hardware or software. A system that supports power management will very likely include a set of registers within the chipset (e.g., the South bridge or ICH) to support power management. For example, a chipset may give system software the ability to select which hardware events will cause the chipset to send a power management notification message to the Host Bridge. Similarly, software (e.g. ACPI software) may access a register, causing a power management to be sent. The actual entity responsible for sending these message to the Host Bridge is the System Management Controller (SMC).