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142 21555 Non-Transparent PCI-to-PCI Bridge User Manual
List of Registers
Table 47. Downstream Configuration Data and Upstream Configuration Data Registers
These registers are also mapped in memory and I/O space. This register is treated as a reserved
register for all memory accesses.
Bit Name R/W Description
31:0
CFG_DATA
(CD)
DCD:
R/(WP)
UCD:
R/(WS)
This register contains the write data driven or the read data returned from a
configuration transaction initiated by the 21555. The Downstream or
Upstream Configuration Address register contains the address for this
transaction, depending on the direction of the transaction.
The transaction is initiated when this register is written (for a configuration
write) or read (for a configuration read) and the corresponding
Configuration Control bit is a one.
The byte enables used for this register access are the same byte enables
used for the transaction driven on the target bus. A target retry is returned to
the initiator until the transaction has been completed on the target bus.
When the semaphore method is used, a master should not write to this
register unless the master has successfully read a 0 from the Downstream
or Upstream Configuration Own bit.
The Downstream Configuration Data register is reserved when accessed
from the secondary interface, or on either interface when the Downstream
Configuration Enable bit is not set.
The Upstream Configuration Data register is reserved when accessed from
the primary interface, or on either interface when the Upstream
Configuration Enable bit is not set.
Table 48. Configuration Own Bits Register
This register is also mapped in memory and I/O space.
• Primary byte offset: 91:90h
• Secondary byte offset: 91:90h
• CSR byte offset 011:010h.
Bit Name R/W Description
0
Downstream
Configuration
Own Bit
R0TS (P)
R(S)
Indicates ownership of the Downstream Configuration Address and
Downstream Configuration Data registers.
• When 0, downstream Configuration Address and Downstream
Configuration Data registers are not owned. When read as a 0
from the primary interface, this bit is subsequently set to a 1 by
the 21555 when the Downstream Configuration Control bit is a 1.
• When 1, a master owns Downstream Configuration Address and
Downstream 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.
Offsets Downstream Configuration Data Upstream Configuration Data
Primary byte 87:84h 8F:8Ch (Reserved)
Secondary byte 87:84h (Reserved) 8F:8Ch
CSR Space 007:004h 00F:00Ch