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21555 Non-Transparent PCI-to-PCI Bridge User Manual 153
List of Registers
Table 66. Primary Latency and Secondary Master Latency Timer Registers
Bit Name R/W Description
7:0
Master
Latency
Timer
R/W
Master latency timer for the corresponding interface. Indicates the number of PCI
clock cycles from the assertion of FRAME# to the expiration of the timer when the
21555 is acting as a master. All bits are writable, resulting in a granularity of 1 PCI
clock cycle.
• When 0, the 21555 relinquishes the bus after the first data transfer when the
21555’s PCI bus grant has been deasserted.
• Reset value is 00h.
Table 67. Header Type Register
• Primary byte offset: 0Eh and 4Eh
• Secondary byte offset: 0Eh and 4Eh
Bit Name R/W Description
7:0
Header
Type
R
Defines the layout of addresses 00h through 3Fh in configuration space.
Reads as 00h indicating a Type 0 header format.
Table 68. BiST Register
The 21555 does not implement self-test internally and does not directly use the BiST register. However, some
form of self
-test may be desired in the subsystem so mechanisms are provided by the 21555 to support
vendor
-specific usage of the BiST register. The default value of this register is 00h after reset assertion, which
indicates that BiST is not supported. However, after reset the 21555 allows this field to be automatically
preloaded with a value from the serial ROM (when attached) or programmed via the secondary interface by
the local process
• Primary byte offset: 0Fh and 4Fh
• Secondary byte offset: 0Fh and 4Fh
Bit Name R/W Description
3:0
Completion
Code
R/(WS)
The completion code can only be written by the secondary interface (at
secondary offset 0Fh or offset 4Fh). A Completion Code value of 0h indicates
that the device passed its self
-test. Any non-zero value in the Completion
Code indicates that the device failed its self
-test.
5:4 Reserved R Reserved. Read only as 0.
6 Self Test R/W
This bit can be written via the primary interface or secondary interface
configuration registers. Configuration code running on the host processor
sets this bit to 1 to invoke self
-test. The local processor (or some other
device) on the secondary interface clears this bit to 0 to indicate the
completion of the self
-test (after first updating the Completion Code bit field).
7
BiST
Supported
R/(WS)
This bit can be written by the secondary interface (at secondary offset 0Fh or
offset 4Fh) or it may be preloaded using the serial ROM. A value of 1
indicates to configuration software that the device supports self
-test. A value
of 0 indicates that the device does not support self
-test.
Offsets Primary MLT Secondary MLT
Primary byte 0Dh 4Dh
Secondary byte 4Dh 0Dh