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346 Hardware Reference Manual
Intel
®
IXP2800 Network Processor
PCI Unit
9.4.2.2 Command Bus Master Access to Local Control and
Status Registers
These are CSRs within the PCI Unit that are accessible from push/pull bus masters. The masters
include the Intel XScale
®
core, Microengines. There is no PCI bus cycles generated. The CSRs
within the PCI Unit can be accessed internally by external PCI devices.
9.4.2.3 Command Bus Master Direct Access to PCI Bus
The Intel XScale
®
core and Microengines are the only command bus masters that have direct
access to the PCI bus as a PCI Bus initiator. The PCI Bus can be accessed by push/pull command
bus access to PCI bus address space. The PCI Unit will share the internal SRAM push/pull data bus
with SRAM for the data transfers.
Data from the SRAM push/pull data bus is transferred through the master data port of the FBus
interface of the PCI core. The PCI Core handles all of the PCI Bus protocol handshakes. The
SRAM pull data received for a write command will be transferred to the Master write FIFO for PCI
writes. For PCI reads, data is transferred from the read FIFO to the SRAM push data bus. A 32-
byte Direct buffer is used to support up to 32 bytes of data responses to the direct access to PCI
Bus.
The Command Bus Master access to the PCI bus will require internal arbitration to gain access to
the data FIFOs inside the core, which are shared between the DMA engine and direct access to
PCI.
9.4.2.3.1 PCI Address Generation for IO and MEM Cycles
When the push/pull command bus master is accessing the PCI Bus, the PCI address is generated
based on the PCI address extension register (PCI_ADDR_EXT). Figure 128 shows how the
address is generated from a Command Bus Master address.
Figure 128. PCI Address Generation for Command Bus Master to PCI
A9775-02
31 2627282930 232425 19202122 15161718 1214 13 891011 45673210
PMSA
PCI Extension
Register
PCI Address for PCI
Memory Accesses
PIOADD
RES
31 2627282930 232425 19202122 15161718 1214 13 891011 45673210
PCI Address for
PCI I/O Accesses
PIOADD 00
31 2627282930 232425 19202122 15161718 1214 13 891011 45673210
PMSA
PIOADD
RES
Intel XScale
®
Core Address[15:2]