Hub Interface to PCI Bridge Registers (D30:F0)
8-6
Intel
82801BA ICH2 Datasheet
8.1.10
PBUS_NUM—Primary Bus Number Register
(HUB-PCI—D30:F0)
Offset Address:
Default Value:
18h
00h
Attribute:
Size:
RO
8 bits
8.1.11
SBUS_NUM—Secondary Bus Number Register
(HUB-PCI—D30:F0)
Offset Address:
Default Value:
19h
00h
Attribute:
Size:
R/W
8 bits
8.1.12
SUB_BUS_NUM—Subordinate Bus Number Register
(HUB-PCI—D30:F0)
Offset Address:
Default Value:
1A
00h
Attribute:
Size:
R/W
8 bits
8.1.13
SMLT—Secondary Master Latency Timer Register
(HUB-PCI—D30:F0)
Offset Address:
Default Value:
1Bh
00h
Attribute:
Size:
R/W
8 bits
This Master Latency Timer (MLT) controls the amount of time that the ICH2 continues to burst
data as a master on the PCI bus. When the ICH2 starts the cycle after being granted the bus, the
counter is loaded and starts counting down from the assertion of FRAME#. If the internal grant to
this device is removed, then the expiration of the MLT counter results in the deassertion of
FRAME#. If the internal grant has not been removed, the ICH2 can continue to own the bus.
Bit
Description
7:0
Primary Bus Number
—RO.
This field indicates the bus number of the hub interface and is hardwired
to 00h.
Bit
Description
7:0
Secondary Bus Number
—R/W.
This field indicates the bus number of PCI. Note that when this
number is equal to the primary bus number (i.e., bus #0), the ICH2 will run hub interface configuration
cycles to this bus number as Type 1 configuration cycles on PCI.
Bit
Description
7:0
Subordinate Bus Number
—R/W.
This field specifies the highest PCI bus number below the hub
interface to PCI bridge. If a Type 1 configuration cycle from the hub interface does not fall in the
Secondary-to-Subordinate Bus ranges of Device 30, the ICH2 indicates a master abort back to the
hub interface.
Bit
Description
7:3
Master Latency Count
—R/W.
This 5-bit value indicates the number of PCI clocks, in 8-clock
increments, that the ICH2 remains as master of the bus.
2:0
Reserved.
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