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21555 Non-Transparent PCI-to-PCI Bridge User Manual 159
List of Registers
12
LUT Page
Size
Extension Bit
R/W
Allows selection of larger page sizes when programming the page size
field in the Chip Control 1 configuration register.
• When 0, page sizes 256 bytes through 4 MB are available in the page
size field.
• When 1, page sizes 8 MB through 32 MB are available in the page
size field.
• Reset value is 0
13 Retry Counter R/W
Disables or enables all 2
24
retry counters in both directions.
• When 0, all 2
24
retry counters are enabled. When the 21555 attempts
a posted write or delayed transaction as a master and receives 2
24
target retries, the 21555 discards the transaction.
• When 1, all 2
24
retry counters are disabled and do not place any limits
on the number of attempts the 21555 makes when initiating a posted
write or delayed transaction.
• Reset value is 0
15:14 VGA Mode R/W
Enables address decoding and transaction forwarding of the following
VGA transactions:
• Frame buffer memory addresses 000BFFFF:000A0000h
• VGA I/O addresses 3BB:3B0h and 3DF:3C0h, where AD[31:16] =
0000h and AD[15:10] are not decoded.
The following values control how the 21555 decodes and forwards VGA
memory and I/O transactions:
• 00: VGA memory and I/O transactions on the primary and secondary
buses are ignored (unless decoded by some other mechanism).
• 01: VGA memory and I/O transactions on the primary bus are
forwarded to the secondary bus. VGA transactions on the secondary
bus are ignored.
• 10: VGA memory and I/O transactions on the secondary bus are
forwarded to the primary bus. VGA transactions on the primary bus
are ignored.
• 11: Illegal.The 21555 behavior is unpredictable.
Reset value is 00b
Table 77. Chip Control 0 Register (Sheet 4 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