
IBM21P100BGC
IBM 133 PCI-X Bridge R2.0
ppb20_pcix_regs.fm.01
October 15, 2001
Configuration Registers
5.2.4.32 Bridge Control Register
This register provides extensions to the command register that are specific to a bridge. The bridge control
register provides many of the same controls for the secondary interface that are provided by the command
register for the primary interface. Some bits affect the operation of both bridge interfaces.
Address Offset
x‘3E’
Access
See individual bit fields. Reads and writes to this register behave normally for all
bits except bit 10. Writes to bit 10 are slightly different as this bit can be reset, but
not set. The bit is reset whenever the register is written, and the data in the corre-
sponding bit location is a ‘1’.
Reset Value
x‘0000’
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15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
Bit(s)
Access
Field Name and Description
15:12
RO
Reserved
11
RW
Discard Timer SERR# Enable
0
Do not assert SERR# on the primary interface as a result of the expiration of either the Primary Dis-
card Timer or Secondary Discard Timer.
1
Assert SERR# on the primary interface as a result of the expiration of either the Primary Discard Timer
or Secondary Discard Timer.
This bit is ignored by a bridge in the PCI-X mode.
10
RW
Discard Timer Status
0
No discard timer error.
1
Discard timer error.
This bit is never set for an interface that is in the PCI-X mode.
9
RW
Secondary Discard Timer
0
Secondary Discard Timer counts 215 PCI clock cycles.
1
Secondary Discard Timer counts 2
10 PCI clock cycles.
Ignored by the bridge if the secondary interface is in the PCI-X mode.
8
RW
Primary Discard Timer
0
Primary Discard Timer counts 215 PCI clock cycles.
1
Primary Discard Timer counts 210 PCI clock cycles.
Ignored by the bridge if the primary interface is in the PCI-X mode.
7
RO
Fast Back-to-Back Enable
0
Bridge does not generate fast back-to-back transactions.