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156 21555 Non-Transparent PCI-to-PCI Bridge User Manual
List of Registers
16.5.3 Device-Specific Control and Status Registers
This section contains information about the device-specific control and status registers.
Table 76. Device-Specific Control and Status Address Map
Byte 3 Byte 2 Byte 1 Byte 0
Primary
Offset
Secondary
Offset
Chip Control 1 Chip Control 0 CCh CCh
Chip Status D0h D0h
Table 77. Chip Control 0 Register (Sheet 1 of 4)
This register may be preloaded by serial ROM or programmed by the local processor before host
configuration.
• Primary byte offset: CD:CCh
• Secondary byte offset: CD:CCh
Bit Name R/W Description
0
Master Abort
Mode
R/W
Controls the 21555’s behavior on the initiator bus when a master abort
termination occurs in response to a delayed transaction initiated by the
21555 on the target bus.
• When 0, the 21555 asserts TRDY# in response to a delayed
transaction, and returns FFFFFFFFh if a read. For posted writes,
SERR is not asserted on the initiator bus.
• When 1, the 21555 returns a target abort in response to a delayed
transaction. For posted writes, SERR will be asserted (if otherwise
enabled) on the initiator bus.
• Reset value is 0
1
Memory Write
Disconnect
Control
R/W
Controls the disconnect boundary for memory writes. This bit does not
apply to MWI commands.
• When 0, the 21555 disconnects memory writes either on an aligned 4
KB boundary, a page boundary less than 4 KB (Upstream Memory
Range 2 only) or when the posted write queue is full.
• When 1, the 21555 disconnects memory write on an aligned cache
line boundary, or when the posted write queue is full.
• Reset value is 0
2
Primary
Master
Timeout
R/W
Sets the maximum number of PCI clock cycles that the 21555 waits for an
initiator on the primary bus to repeat a delayed transaction request. The
counter starts when the delayed transaction completion is ready to be
returned to the initiator. When the initiator has not repeated the transaction
at least once before the counter expires, the 21555 discards the delayed
transaction from its queues.
• When 0, the primary master timeout counter is 2
15
PCI clock cycles, or
0.983 ms for a 33
-MHz bus.
• When 1, the value is 2
10
PCI clock cycles, or 30.7 µs for a 33-MHz
bus.
• Reset value is 0