82801CA Datasheet, PDF (142/521 Pages) Intel Corporation – I/O Controller Hub 3-S (ICH3-S)

Functional Description
5.12.6.2
5.12.7
Transition Rules Among S0/Cx and Throttling States
The following priority rules and assumptions apply among the various S0/Cx and throttling states:
• Entry to any S0/Cx state is mutually exclusive with entry to any S1–S5 state. This is because
the processor can only perform one register access at a time and Sleep states have higher
priority than thermal throttling.
• When the SLP_EN bit is set (system going to a sleep state (S1–S5), the THTL_EN bit can be
internally treated as being disabled (no throttling while going to sleep state). Note that thermal
throttling (based on THRM# signal) cannot be disabled in an S0 state. However, once the
SLP_EN bit is set, the thermal throttling is shut off (since STPCLK# will be active in S1–S5
states).
• If the THTL_EN bit is set, and a Level 2 read then occurs, the system should immediately go
and stay in a C2 state until a break event occurs. A Level 2 read has higher priority than the
software initiated throttling or thermal throttling.
• If Thermal Override is causing throttling, and a Level 2read then occurs, the system will stay
in a C2 state until a break event occurs. A Level 2 read has higher priority than the Thermal
Override.
• After an exit from a C2 state (due to a Break event), and if the THTL_EN bit is still set, or if a
Thermal Override is still occurring, the system will continue to throttle STPCLK#. Depending
on the time of break event, the first transition on STPCLK# active can be delayed by up to one
THRM period (1024 PCI clocks=30.72 microseconds).
• The Host controller must post Stop-Grant cycles in such a way that the processor gets an
indication of the end of the special cycle prior to the ICH3 observing the Stop-Grant cycle.
This ensures that the STPCLK# signals stays active for a sufficient period after the processor
observes the response phase.
• If in the C1 state and the STPCLK# signal goes active, the processor will generate a Stop-
Grant cycle, and the system should go to the C2 state. When STPCLK# goes inactive, it should
return to the C1 state.
Sleep States
The ICH3 directly supports different sleep states (S1–S5), which are entered by setting the
SLP_EN bit, or due to a Power Button press. The entry to the Sleep states are based on several
assumptions:
• Entry to a Cx state is mutually exclusive with entry to a Sleep state. This is because the
processor can only perform one register access at a time. A request to Sleep always has higher
priority than throttling.
• Prior to setting the SLP_EN bit, the software will turn off processor-controlled throttling. Note
that thermal throttling cannot be disabled, but setting the SLP_EN bit will disable thermal
throttling (since S1–S5 sleep state has higher priority).
• The G3 state cannot be entered via any software mechanism. The G3 state indicates a
complete loss of power.
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Intel^® 82801CA ICH3-S Datasheet