
SiS5595 PCI System I/O Chipset
Preliminary V2.0 Nov. 2, 1998 21 Silicon Integrated Systems Corporation
Else Leave CKE_N, and CKE_S as they are ;
While in the G1 State, a set of Wake_Up Events can be enabled to transit the system state
back to G0. Please refer to “
RTC APC ”
illustrating the supported wake up events in S3
State.
G2---S4/S5(Suspend To Disk/Soft Off)
The G2 soft-off state is an O.S. initiated system shutdown. The State can be initiated by
programming the SLP_TYPx field with S5 value and setting the SLP_ENx bit high. Also, a
hardware event, which is driven by pressing the power button for more than four seconds
can transit the system to the G2 state while it is in the G0 state. This hardware event is
called a Power Button Over-ride, and is mainly provided to turn off a hung system in case.
Putting system in the G2 state will de-assert PS_ON# eventually from hardware point of
view.
In the G2 State, only the RTC power is alive. While in the G2 state, the SiS5595 could sense
the following seven power up events to transit the system to the Legacy system state by
asserting the PS_ON#. They are RTC Alarm On event, Power Button Up (PWRBT#) event,
Ring Up event, PME0# event, PME1# event, Hotkey Match event, and Password Match
event. Please see the APC portion of the RTC module for more details.
Processor Power State
STPCLK# Throttling (C0)
SiS5595 supports the four power states in the G0/S0 working state. While in the C0 state, it
provides programmable throttling function to place the processor executing at a designated
performance level relative to its maxima performance. This can be achieved by programming
the Throttling Duty Cycle Control field (ACPI: 0Ch[3:1]) with desired value, and setting
Throttling Function Enable bit (ACPI: 0Ch[4]) to HIGH.
CPU Power State Level 1 (C1)
The C1 State is supported through the HLT instruction. For instance, the execution of a
HALT instruction will cause CPU to automatically enter the Auto HALT Power down state
where Icc of the processor will be -20% of the Icc in the Normal State. In this state, the CPU
will transit to the Normal state upon the occurrence of INTR, NMI, SMI#, RESET, or INIT.
CPU would not recognize AHOLD, BOFF#, and EADS# for cache invalidation or write-back.
That is, the system is no longer able to allow bus master snooping, or memory access. As
such, C2 low power state provides an alternative not to block bus master streaming while the
CPU is put into the low power state.