
82371AB (PIIX4)
E
122
4/9/97 2:23 PM PIIX4aDS
INTEL CONFIDENTIAL
(until publication date)
PRELIMINARY
Bit
Description
23
Reserved.
Read as 0.
22:18
Bus Master Timer Count (BM_CNT)—R/W.
Specifies the initial and reload count of the device 8
(parallel port and PCI bus master) idle timer.
17:16
Reserved.
Read as 0.
15
Device 8 Idle Timer Resolution (IDL_SEL_DEV8)—R/W.
Selects the clock source for the
device 8 (parallel port) idle timer. 0=1 second granular. 1=1 ms granular.
14
ZZ Enable (ZZ_EN)—R/W.
1=Enable PIIX4 assertion of the ZZ signal. 0=Disable. When enabled,
PIIX4 will assert ZZ signal under certain conditions when entering clock control mode. Whether or
not ZZ is asserted depends on:
1.
2.
3.
Time from STPCLK# assertion to Stop Grant cycle.
Frequency of any enabled Stop Break or Burst events.
Programmed throttle duty cycle if throttling enabled.
NOTE
The L2 cache can not be snooped with ZZ signal asserted; therefore, must be disabled in Level
2 power state such as Stop Grant.
13:11
Thermal Duty Cycle (THRM_DTY)—R/W.
This 3-bit field determines the duty cycle for the clock
control thermal throttling mode (THRM# is asserted). The duty cycle indicates the percentage of time
the STPCLK# signal is asserted while in the thermal throttle mode. The field is decoded as follows:
Bits[13:11]
000
001
010
011
Mode
Reserved
12.5%
25%
37.5%
Bits[13:11]
100
101
110
111
Mode
50%
62.5%
75%
87.5%
NOTE
Software must set this 3-bit field to a non-zero value for proper operation.
10:6
Processor PLL Lock Count (CPU_LCK)—R/W.
Specifies the initial count of fast burst timer when
used to measure the processor PLL lock time. The fast burst timer is loaded with the CPU_LCK
value and the appropriate clock source selected when the processor transitions from the stop clock
or deep sleep state.
5
Processor PLL Lock Resolution (CPU_SEL)—R/W.
Selects the clock resolution used for the fast
burst timer when it is used to count the processor’s PLL lock time. 0=1 ms granular. 1=1
μ
s granular.
Fast Burst Timer Count (FB_CNT)—R/W.
Specifies the initial and reload count of fast burst timer.
4:0