Pci-To-Ahb Address Translation; Ahb Master Writes - Intel IXP45X Developer's Manual

®
PCI Controller—Intel IXP45X and Intel
Since the PCI controller performs pre-fetches when doing reads to the PCI_BAR0/1/2/3
address windows, the PCI_AHBMEMBASE must not be programmed to access any AHB
I/O space or the AHB Queue Manager. To access AHB I/O space or the AHB Queue
Manager, PCI_BAR5 must be used.
Figure 91.

PCI-to-AHB Address Translation

pci_bar0
AHBbase0
10.3.2.8

AHB Master Writes

If the AHB Master Interface receives a Memory Write or Memory Write and Invalidate
command from the PCI target, the BAR ID and byte enables are examined to determine
the appropriate operation:
• If the BAR ID indicates a CSR access (BAR 4), CSR access is requested and, when
granted, the indicated write is performed using the supplied address, data, and
byte enables. An AHB master operation is not performed.
• If the BAR ID indicates a memory access (BARs 0-3), the byte enables
corresponding to each word of the transfer are examined to determine the AHB
address and burst size to use during the transfer. If all byte enables are asserted,
an INCR word operation is started on the bus and continues until either the last-
data-word indicator is detected, or a word with at least one byte enable de-
asserted is encountered. Words received from the Initiator Receive FIFO without all
byte enables asserted produce a single byte write operation for each byte that is
enabled. PCI Memory writes produce SINGLE or INCR writes on the AHB bus.
• If the BAR ID indicates an I/O access (BAR5), a single word write is performed if all
byte enables are asserted, otherwise, a single byte write operation is performed for
each byte that is enabled.
August 2006
Order Number: 306262-004US
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IXP46X Product Line of Network Processors
pci_bar1 pci_bar2
AHBbase1 AHBbase2
31 24 23
Intel
pci_bar3
pci_ahbmembase
AHBbase3
register
PCI Address [23:2]
AHB Address [31:0]
® ®
IXP45X and Intel IXP46X Product Line of Network Processors
PCI Byte Enables
encode
2 1 0
B4281-01
Develepor's Manual
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