876784 Intel, 876784 Datasheet - Page 177

• Manufacturer Part Number: 876784
• Manufacturer: Intel

Specifications of 876784

• Lead Free Status / RoHS Status: Compliant

Functional Description
5.14.13
5.14.13.1
5.14.13.2
Intel
®
ICH7 Family Datasheet
Legacy Power Management Theory of Operation
Instead of relying on ACPI software, legacy power management uses BIOS and various
hardware mechanisms. The scheme relies on the concept of detecting when individual
subsystems are idle, detecting when the whole system is idle, and detecting when
accesses are attempted to idle subsystems.
However, the operating system is assumed to be at least APM enabled. Without APM
calls, there is no quick way to know when the system is idle between keystrokes. The
ICH7 does not support burst modes.
APM Power Management (Desktop Only)
The ICH7 has a timer that, when enabled by the 1MIN_EN bit in the SMI Control and
Enable register, generates an SMI# once per minute. The SMI handler can check for
system activity by reading the DEVACT_STS register. If none of the system bits are set,
the SMI handler can increment a software counter. When the counter reaches a
sufficient number of consecutive minutes with no activity, the SMI handler can then put
the system into a lower power state.
If there is activity, various bits in the DEVACT_STS register will be set. Software clears
the bits by writing a 1 to the bit position.
The DEVACT_STS register allows for monitoring various internal devices, or Super I/O
devices (SP, PP, FDC) on LPC or PCI, keyboard controller accesses, or audio functions
on LPC or PCI. Other PCI activity can be monitored by checking the PCI interrupts.
Mobile APM Power Management (Mobile/Ultra Mobile Only)
In mobile/ultra mobile systems, there are additional requirements associated with
device power management. To handle this, the ICH7 has specific SMI# traps available.
The following algorithm is used:
The SMI# handler exits with an I/O restart. This allows the original software to
continue.
1. The periodic SMI# timer checks if a device is idle for the required time. If so, it puts
2. When software (not the SMI# handler) attempts to access the device, a trap occurs
3. The SMI# handler turns on the device and turns off the trap
the device into a low-power state and sets the associated SMI# trap.
(the cycle does not really go to the device and an SMI# is generated).
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