Intel
82801BA ICH2 Datasheet
5-71
Functional Description
Table 5-40
shows which events can cause an SMI# and SCI. Note that some events can be
programmed to cause either an SMI# or SCI. The usage of the event for SCI (instead of SMI#) is
typically associated with an ACPI-based system. Each SMI# or SCI source has a corresponding
enable and status bit.
Notes on causes of SCI and SMI:
1. SCI_EN must be 1 to enable SCI. SCI_EN must be 0 to enable SMI
2. SCI can be routed to cause interrupt 9:11 or 20:23 (20:23 only available in APIC mode)
3. GBL_SMI_EN must be 1 to enable SMI
4. EOS must be written to 1 to re-enable SMI for the next one
Table 5-40. Causes of SMI# and SCI
Event
SMI
SCI
Comment
PCI PME# assertion
Yes
Yes
Can also cause Wake Event
PWRBTN# assertion
Yes
Yes
Can also cause Wake Event
RTC Alarm
Yes
Yes
RI# (Ring Indicate) assertion
Yes
Yes
AC ‘97 wake event
Yes
Yes
USB wake events
Yes
Yes
THRM# pin active (based on
THRM#_POL)
Yes
Yes
The THRM# can cause an SMI# or SCI on either the
rising or falling edge. Causes SCI if SCI_EN is set,
causes SMI# if SCI_EN not set.
ACPI Timer overflow (2.34s)
Yes
Yes
Any GPI
Yes
Yes
TCO event (includes SERR#)
Yes
Yes
Can also cause IRQ (other than SCI).
BIOS_STS bit set
Yes
No
ACPI code in OS sets GBL_RLS bit to cause BIOS_STS
bit active, which causes SMI#.
GBL_STS bit set
No
Yes
This bit is set when the BIOS sets the BIOS_RLS bit.
The ACPI handler will clear the bit.
Write access to APM control
register
Yes
No
OS or BIOS writes to the APMC register. SMM handler
clears.
Periodic Timer expires
Yes
No
SW SMI timer expires
Yes
No
Allows SMM handler to exit temporarily. Another SMI#
occurs about 64 ms later.
LEGACY_USB_STS bit set
Yes
No
Bit set based on address decode or incoming USB IRQ.
Serial IRQ SMI
Yes
No
Device Trap
Yes
No
Indicates that subsystems may need to be powered
back on.
SMBus Host Controller
Yes
No
SMBus Slave SMI
Yes
No
Global Standby Timer expires in
S1 state
Yes
No
Access to Microcontroller range
Yes
No
Access to Microcontroller range (62h/66h) with
MCSMI_EN set.
SLP_EN bit set
Yes
No
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