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21555 Non-Transparent PCI-to-PCI Bridge User Manual 143
List of Registers
7:1 Reserved R Read only as 0.
8
Upstream
Configuration
Own Bit
R0TS (S)
R(P)
Indicates ownership of the Upstream Configuration Address and
Upstream Configuration Data registers.
• When 0, upstream Configuration Address and Upstream
Configuration Data registers are not owned. When read as a 0
from the secondary interface, this bit is subsequently set to a 1 by
the 21555 if the Upstream Configuration Control bit is a 1.
• When 1, a master owns Upstream Configuration Address and
Upstream Configuration Data registers. When this semaphore
method is used, other masters should not attempt to access
these registers when this bit is a 1. This bit is automatically
cleared once the configuration transaction has completed on the
initiator bus.
• Reset value is 0.
15:9 Reserved R Read only as 0.
Table 49. Configuration CSR (Sheet 1 of 2)
This register is also mapped in memory and I/O space.
• Primary byte offset: 93:92h
• Secondary byte offset: 93:92h
• CSR byte offset: 013:012h
Bit Name R/W Description
0
Downstream
Configuration
Own Status
R
Provides the current value of the Downstream Configuration Own bit. This
bit has no side effects when read.
1
Downstream
Configuration
Control
R/W
Enables the 21555 to perform downstream indirect configuration
transactions.
• When 0, the 21555 will not initiate a configuration transaction on the
secondary interface when the Downstream Configuration Data
register is accessed. The Downstream Configuration Data register is
treated as a reserved register.
• When 1, the 21555 is enabled to perform downstream configuration
transactions when the Downstream Configuration Data register is
accessed.
• Reset value is 0
2
Downstream
Self
-Response
Enable
R/W
Controls the 21555 ability to respond to a configuration transaction that it
generates as a master.
• When 0, the 21555 does not respond to configuration transactions
that it generates.
• When 1, the 21555 does not respond to configuration transactions
that it generates as a master.
• Reset value is 0
7:3 Reserved R Reserved. Returns 0 when read.
8
Upstream
Configuration
Own Status
R
Provides the current value of the Upstream Configuration Own bit. This bit
has no side effects when read.
Table 48. Configuration Own Bits Register