Functional Description
5-78
Intel
82801BA ICH2 Datasheet
5.12.7.4
Processor-Initiated Passive Cooling (Via Programmed Duty Cycle on
STPCLK#)
Using the THTL_EN and THTL_DTY bits, the ICH2 can force a programmed duty cycle on the
STPCLK# signal. This reduces the effective instruction rate of the processor and cut its power
consumption and heat generation.
5.12.7.5
Active Cooling
Active cooling involves fans. The GPIO signals from the ICH2 can be used to turn on/off a fan.
5.12.8
Event Input Signals and Their Usage
The ICH2 has various input signals that trigger specific events. This section describes those signals
and how they should be used.
5.12.8.1
PWRBTN# — Power Button
The ICH2 PWRBTN# signal operates as a “Fixed Power Button” as described in the ACPI
specification. PWRBTN# signal has a 16 ms de-bounce on the input. The state transition
descriptions are included in the following table. Note that the transitions start as soon as the
PWRBTN# is pressed (but after the debounce logic), and does not depend on when the Power
Button is released.
Power Button Override Function
If PWRBTN# is observed active for at least 4 consecutive seconds, the state machine should
unconditionally transition to the G2/S5 state, regardless of present state (S0–S4). In this case, the
transition to the G2/S5 state should not depend on any particular response from the processor
(e.g., a Stop-Grant cycle), nor any similar dependency from any other subsystem.
The PWRBTN# status is readable to check if the button is currently being pressed or has been
released. The status is taken after the de-bounce, and is readable via the PWRBTN_LVL bit.
Note:
The 4-second PWRBTN# assertion should only be used if a system lock-up has occurred. The
4-second timer starts counting when the ICH2 is in a S0 state. If the PWRBTN# signal is asserted
and held active when the system is in a suspend state (S1–S5), the assertion causes a wake event.
Once the system has resumed to the S0 state, the 4-second timer starts.
Table 5-47. Transitions Due to Power Button
Present
State
Event
Transition/Action
Comment
S0/Cx
PWRBTN# goes low
SMI# or SCI generated
(depending on SCI_EN)
Software will typically initiate a
Sleep state.
S1
–
S5
PWRBTN# goes low
Wake Event. Transitions to S0
state.
Standard wakeup
G3
PWRBTN# pressed
None
No effect since no power.
Not latched nor detected.
S0
–
S4
PWRBTN# held low for
at least 4 consecutive
seconds
Unconditional transition to S5
state.
No dependence on processor
(such as Stop-Grant cycles) or
any other subsystem.
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