82801DB Datasheet, PDF (359/587 Pages) Intel Corporation – Intel 82801DB I/O Controller Hub 4 (ICH4)

LPC Interface Bridge Registers (D31:F0)
Bit
Description
THRM_DTY — R/W. This write-once 3-bit field determines the duty cycle of the throttling when the
thermal override condition occurs. The duty cycle indicates the approximate percentage of time the
STPCLK# signal is asserted while in the throttle mode. The STPCLK# throttle period is 1024
PCICLKs. Note that the throttling only occurs if the system is in the C0 state. If in the C2 state, no
throttling occurs.
There is no enable bit for thermal throttling, because it should not be disabled. Once the
THRM_DTY field is written, any subsequent writes will have no effect until PCIRST# goes active.
THRM_DTY
Throttle Mode
PCI Clocks
7:5 000
50% (Default)
512
001
87.5%
896
010
75.0%
768
011
62.5%
640
100
50%
512
101
37.5%
384
110
25%
256
111
12.5%
128
THTL_EN — R/W. When set and the system is in a C0 state, it enables a processor-controlled
STPCLK# throttling. The duty cycle is selected in the THTL_DTY field.
4
0 = Disable
1 = Enable
THTL_DTY — R/W. This 3-bit field determines the duty cycle of the throttling when the THTL_EN bit
is set. The duty cycle indicates the approximate percentage of time the STPCLK# signal is asserted
(low) while in the throttle mode. The STPCLK# throttle period is 1024 PCICLKs.
THTL_DTY
Throttle Mode
PCI Clocks
000
50% (Default)
512
001
87.5%
896
3:1 ₀₁₀
75.0%
768
011
62.5%
640
100
50%
512
101
37.5%
384
110
25%
256
111
12.5%
128
0 Reserved
9.8.3.6
LV2 — Level 2 Register
I/O Address:
Default Value:
Lockable:
Power Well:
PMBASE + 14h
(ACPI P_BLK+4)
00h
No
Core
Attribute:
Size:
Usage:
RO
8 bit
ACPI or Legacy
Bit
Description
Reads to this register return all zeros, writes to this register have no effect. Reads to this register
7:0
generate a “enter a level 2 power state” (C2) to the clock control logic. This will cause the STPCLK#
signal to go active, and stay active until a break event occurs. Throttling (due either to THTL_EN or
THRM# override) will be ignored.
Intel^® 82801DB ICH4 Datasheet
359