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Hardware Reference Manual 355
Intel
®
IXP2800 Network Processor
PCI Unit
The BE_DEMI bit of the PCI_CONTROL register can be set to enable big-endian on the incoming
data from the PCI Bus to both the SRAM and DRAM. The BE_DEMO bit of the PCI_CONTROL
register can be set to enable big-endian on the outgoing data to the PCI Bus from both the SRAM
and DRAM.
9.6.1 Endian for Byte Enable
During any endian conversion, PCI does not need to do any longword byte enable swapping
between two 32-bit longwords (LW1, LW0). But PCI may need to do byte enable swapping within
the 32-bit longword byte enable. Because of the different endian convention between PCI Bus and
the memory, all data going between the PCI core FIFO and memory data bus passes through the
byte lane reversal as shown in Table 138 through Table 145:
Table 138. Byte Enable Alignment for 64-Bit PCI Data In (64 Bits PCI Little-Endian to Big-
Endian with Swap)
PCI Data
IN_BE[7] IN_BE[6] IN_BE[5] IN_BE[4] IN_BE[3] IN_BE[2] IN_BE[1] IN_BE[0]
SRAM Data
OUT_BE[3] OUT_BE[2] OUT_BE[1] OUT_BE[0] OUT_BE[0] OUT_BE[1] OUT_BE[2] OUT_BE[3]
Longword1byte enable
LW1 byte enable drive after LW0 byte enable
Longword0 byte enable
LW0 byte enable drive first
DRAM Data
OUT_BE[4] OUT_BE[5] OUT_BE[6] OUT_BE[7] OUT_BE[0] OUT_BE[1] OUT_BE[2] OUT_BE[3]
Table 139. Byte Enable Alignment for 64-Bit PCI Data In (64 Bits PCI Big-Endian to Big-Endian
without Swap)
PCI Data
IN_BE[4] IN_BE[5] IN_BE[6] IN_BE[7] IN_BE[0] IN_BE[1] IN_BE[2] IN_BE[3]
SRAM Data
OUT_BE[0] OUT_BE[1] OUT_BE[2] OUT_BE[3] OUT_BE[0] OUT_BE[1] OUT_BE[2] OUT_BE[3]
Longword1byte enable
LW1 byte enable drive after LW0 byte enable
Longword0 byte enable
LW0 byte enable drive first
DRAM Data
OUT_BE[4] OUT_BE[5] OUT_BE[6] OUT_BE[7] OUT_BE[0] OUT_BE[1] OUT_BE[2] OUT_BE[3]
Table 140. Byte Enable Alignment for 32-Bit PCI Data In (32 bits PCI Little-Endian to Big-
Endian with Swap)
PCI Add[2]=1 PCI Add[2]=0
Longword1byte enable
LW1 byte enable drive after LW0 byte enable
Longword0 byte enable
LW0 byte enable drive first
PCI Data
IN_BE[3] IN_BE[2] IN_BE[1] IN_BE[0] IN_BE[3] IN_BE[2] IN_BE[1] IN_BE[0]
SRAM Data
OUT_BE[0] OUT_BE[1] OUT_BE[2] OUT_BE[3] OUT_BE[0] OUT_BE[1] OUT_BE[2] OUT_BE[3]
Longword1byte enable
LW1 byte enable drive after LW0 byte enable
Longword0 byte enable
LW0 byte enable drive first
DRAM Data
OUT_BE[4] OUT_BE[5] OUT_BE[6] OUT_BE[7] OUT_BE[0] OUT_BE[1] OUT_BE[2] OUT_BE[3]