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Functional Description
5-54
82801AA and 82801AB Datasheet
It is important to understand that the various GPIs have different levels of functionality when used
as wake events. The GPIs that reside in the core power well can only generate wake events from an
S1 state. Also only certain GPIs are “ACPI Compliant,” meaning that their Status and Enable bits
reside in ACPI I/O space.
Table 5-39
summarizes the use of GPIs as wake events.
The latency to exit the various Sleep states varies greatly and is heavily dependent on power supply
design. Approximations are shown in
Table 5-40
. The time indicates from when the Wake event
occurs (signal transition) to when the processor is allowed to start its first cycle (CPURST# goes
inactive). There are very large additional delays for the processor to execute sufficient amounts of
BIOS to invoke the OS (such as coming out of S1-S3) or spinning up the hard drive (such as
coming out of S4 or S5).
5.12.5.4
Sx-G3-Sx, Handling Power Failures
Power failures can occur if the AC power is cut (a real power failure) or if the system is unplugged.
Depending on when the power failure occurs and how the system is designed, different transitions
could occur due to a power failure.
The AFTER_G3 bit provides the ability to program whether or not the system should boot once
power returns after a power loss event. If the policy is to not boot, the system remains in an S5 state
(unless previously in S4). There are only three possible events that wake the system after a power
failure.
1. PWRBTN#: PWRBTN# is always enabled as a wake event. When RSMRST# is low
(G3 state), the PWRBTN_STS bit is reset. When the ICH exits G3 after power returns
(RSMRST# goes high), the PWRBTN# signal is already high (because Vcc-standby goes high
before RSMRST# goes high) and the PWRBTN_STS bit is 0.
2. RI#: RI# does not have an internal pull-up. This signal should be pulled-up to the suspend well
supply. After recovery from a power failure, the ICH samples RI# after RSMRST# is sampled
deasserted. At that time, RI# will be high (deasserted). The bit that enables RI# as a wake
event is preserved across power failures in the RTC Well supply.
3. RTC Alarm. The RTC_EN bit is in the RTC well and is preserved after a power loss. Like
PWRBTN_STS the RTC_STS bit is cleared when RSMRST# goes low.
Table 5-39. GPI Wake Events
GPI
Power Well
Wake From
Notes
GPI[1:0], GPI[7:5]
Core
S1
GPI[13:8]
Resume
S1-S5
ACPI Compliant
GPIO[28:27]
Resume
S1-S5
Table 5-40. Sleep State Exit Latencies
State
Latency
S1
<1 ms. Based on wake event to STPCLK# high + re-enumeration of PCI bus, USB, CardBus, etc.
Must also add PLL spin-up times
S3
Power Supply ramp + 20 ms
S4
Power Supply ramp + 20 ms
S5
Power Supply ramp + 20 ms