Revision 1.02 – June 27, 2006
S5935 – PCI Product
Data Book
The configurable FIFO advance condition may be
used to transfer data to and from Add-On interfaces
which are not 32-bits wide. For a 16-bit Add-On bus,
the Add-On to PCI FIFO advance condition can be set
to byte 2. This allows a 16-bit write to the lower 16-bits
of the FIFO register (bytes 0 and 1) and a second write
to the upper 16-bits of the FIFO register (bytes 2 and
3). The FIFO does not advance until the second
access. This allows the Add-On to operate with 16-bit
data, while the PCI bus maintains a 32-bit data path.
Endian Conversion
Bits D31:30 and D25:24 of the INTCSR PCI Operation
Register control endian conversion operations for the
FIFO (Figure 1). When endian conversion is per-
formed, it affects data passing in either direction
through the FIFO interface. Figures 2a and 2b show
16-bit and 32-bit endian conversion. It is important to
note that endian conversion is performed on data BE-
FORE it enters the FIFO. This affects the FIFO
advance condition. Example: the FIFO is configured to
perform 32-bit endian conversion on data, and the
FIFO advance condition is set to byte 0. Byte 3 is writ-
ten into the FIFO (BE3# asserted). After the endian
conversion, byte 3 becomes byte 0, and the FIFO
advances. This behavior must be considered when not
performing full 32-bit accesses to the FIFO.
Figure 73. Figure 2a. 16-bit Endian Conversion
DESTINATION
D 31-24
D 15-8
D 7-0
D 23-16
Figure 2b. 32-bit Endian Conversion
DESTINATION
BYTE 2
BYTE 3
BYTE 1 BYTE 0
D 31-24
BYTE 3
D 15-8
D 7-0
D 23-16
BYTE 2
BYTE 1
BYTE 0
BYTE 2
D 23-16
BYTE 3
D 31-24
BYTE 1
D 15-8
BYTE 0
D 7-0
SOURCE
BYTE 3
D 31-24
BYTE 2
D 23-16
BYTE 1 BYTE 0
Notes:
1. During operation, the INTCSR FIFO advance condition bits
(D29:26) should only be changed when the FIFO is empty and is
idle on both the Add-On and PCI interfaces.
D 15-8
D 7-0
SOURCE
Notes:
1. During operation, the INTCSR FIFO endian conversion bits
(D25:24) and 64-bit access bits (D31:30) should only be changed
when the FIFO is empty and is idle on both the Add-On and PCI
interfaces.
AMCC Confidential and Proprietary
DS1527
135
AMCC [ APPLIED MICRO CIRCUITS CORPORATION ]
