Broadcom BCM5722 - Figure 80: Power Management Configuration During POST

Programmer’s Guide BCM5722
10/15/07
Broadcom Corporation
Document 5722-PG101-R PCI Page 528
The ACPI specification refers to SMM as a legacy mode and prefers the native O/S (i.e., Microsoft Windows, Linux
®
, etc.)
to handle the interrupt. The essential problem with using SMI, resides in moving the processor into SMM mode; the native
OS does not have visibility into the event. To solve this design constraint, the ACPI 2.0 specification defines a System
Control Interrupt. SCI will notify an OS of a power management event. The SCI is a shared, level triggered interrupt.
Figure 80 shows how a system BIOS would configure power management to use either SMM or SCI during the system
POST. A SCI_Enable will route power management events to the SCI interrupt arbiter, rather than SMI arbiter.
Figure 80: Power Management Configuration During POST
The arbiter is combinational logic residing in the chipset and contains status/control registers for power management. The
host chipset provides General-Purpose Event registers (GPE, see Figure 81) to selectively enable/disable PM events. The
GPE block also contains status registers to record the PM event’s occurrence. All the PM events are mapped into a single-
level triggered SCI. The SCI may be routed to either a PIC or APIC. How the SCI is routed is not important for this discussion
and will depend upon the host motherboard. The SCI interrupt will be serviced by an ACPI OS, which is the important differ-
entiator. Under SMM mode, the OS would not be notified of the PM event. With an interrupt, the OS will branch to a service
routine for the SCI vector. The ACPI driver will have an AML event routine, which will operate upon the PM event accordingly.
Refer to the ACPI 2.0 specification for a detailed explanation of how AML and ACPI tables interact. A PME signal can be
routed into the GPE block, which ties networking wake-capable devices into the ACPI model.
SMI Arbiter
SCI_Enable
Device
Events
SCI Arbiter
Legacy Idle/Service
Timers
SCI#
Decoder
S1
D1
D2ENB
SMI#
Thermal
Events
User Events
(Power Button)