Intel 460GX 16.3Handling of Power Failures in IFB

IFB Power Management

A Wake event will cause an exit from the Soft-Off state. The wake events that can wake from the

S5 state are:

S5 Wake Event	Comment
RTC Alarm cause RTC_STS bit set	RTC_EN must be set for the wake event
Power button press causes PWRBTN_STS bit set	Power Button is unconditional wake event
Ring Indicate causes RI_STS bit set	RI_EN must be set for the wake event
GPIO Routed to SCI goes active	EXTSCI_EN must be set for the wake event
GPIO Routed to SMI goes active	EXTSMI_EN must be set for the wake event

16.3Handling of Power Failures in IFB

A power failure is defined as any one of the following:

•PWROK goes low and the IFB did not yet cause SUSB and/or SUSC to go inactive.

•Power to the Resume plane (as detected by RSMRST# or VccRESUME) goes inactive.

Upon detection of a power failure, the state machine will go to the G3 state and the IFB will set a new status bit called PWR_FAIL. That bit can be cleared only by writing a 1 to that bit position.

Add new config bit, AFTERG3, powered off RTC well to indicate what should be done after power failure:

•1 = Return to S4/S5 state (see table below), 0 = Cold Boot.

•Software should set this bit prior to going to an S4 or S5 state if it desires the system to return there after the power failure. This bit is automatically set to 1 due to a Power Button Override event.

When RSMRST# (or the Resume Vcc) is inactive after a power failure, the state machine will transition based on the following table:

State Prior to Power Failure	AFTERG3	Action after Power Returns
S0, S1	0	Cold boot to return to S0 state. SUSB and SUSC go inactive.
S0, S1	1	No boot. SUSB and SUSC stay active (S5 state) until wake
		event.
S4	0	Cold boot to return to S0 state. SUSB and SUSC go inactive.
S4	1	No boot. SUSB and SUSC stay active (S4 state) until wake
		event.
S5	0	Cold boot to return to S0 state. SUSB and SUSC go inactive.
S5	1	No boot. SUSB and SUSC stay active (S5 state) until wake
		event.

If USB devices are attached, setting the AFTERG3 bit to 1 may not be a good idea, since the USB devices will lose their configuration during the power failure and may no longer be able to generate a wake events when the power is restored. In this case, the system may have to always boot after a power failure (except if placed into the S5 state due to Power Button Override).

Intel® 460GX Chipset Software Developer’s Manual 16-5