82801DB Datasheet, PDF (297/587 Pages) Intel Corporation – Intel 82801DB I/O Controller Hub 4 (ICH4)

LPC Interface Bridge Registers (D31:F0)
9.1.12
9.1.13
BIOS_CNTL—BIOS Control Register (LPC I/F—D31:F0)
Offset Address:
Default Value:
Lockable:
4E–4Fh
0000h
No
Attribute:
Size:
Power Well:
R/W
16 bit
Core
Bit
Description
15:2 Reserved
BIOS Lock Enable (BLE) — R/W.
1
0 = Setting the BIOSWE will not cause Sums. Once set, this bit can only be cleared by a
PCIRST#.
1 = Enables setting the BIOSWE bit to cause Sums.
BIOS Write Enable (BIOSWE) — R/W.
0 = Only read cycles result in FWH I/F cycles.
0
1 = Access to the BIOS space is enabled for both read and write cycles. When this bit is written
from a 0 to a 1 and BIOS lock Enable (BLE) is also set, an SMI# is generated. This ensures
that only SMI code can update BIOS.
TCO_CNTL — TCO Control (LPC I/F — D31:F0)
Offset Address: 54h
Default Value: 00h
Lockable:
No
Attribute:
Size:
Power Well:
R/W
8 bit
Core
Bits
Description
7:4 Reserved
TCO Interrupt Enable (TCO_INT_EN) — R/W. This bit enables/disables the TCO interrupt.
3
0 = Disables TCO interrupt.
1 = Enables TCO Interrupt, as selected by the TCO_INT_SEL field.
TCO Interrupt Select (TCO_INT_SEL) — R/W. This field specifies on which IRQ the TCO will
internally appear. If not using the APIC, the TCO interrupt must be routed to IRQ9:11, and that
interrupt is not sharable with the SERIRQ stream, but is shareable with other PCI interrupts. If
using the APIC, the TCO interrupt can also be mapped to IRQ20:23, and can be shared with other
interrupt. Note that if the TCOSCI_EN bit is set (bit 6 of the GPEO_EN register), then the TCO
interrupt will be sent to the same interrupt as the SCI, and the TCO_INT_SEL bits will have no
meaning. When the TCO interrupt is mapped to APIC interrupts 9, 10 or 11, the signal is active
high. When the TCO interrupt is mapped to IRQ 20, 21, 22, or 23, the signal is active low and can
be shared with PCI interrupts that may be mapped to those same signals (IRQs).
2:0 000 = IRQ9
001 = IRQ10
010 = IRQ11
011 = Reserved
100 = IRQ20 (Only available if APIC enabled)
101 = IRQ21 (Only available if APIC enabled)
110 = IRQ22 (Only available if APIC enabled)
111 = IRQ23 (Only available if APIC enabled)
Intel^® 82801DB ICH4 Datasheet
297