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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors—Functional Overview
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
Developer’s Manual
August 2006
50
Reference Number: 306262-004US
The AHB/AHB bridge will complete the write on the South AHB, when it can obtain
access to the peripheral on the South AHB. The North AHB is released to complete
another transaction.
When a transaction is “split,” a master on the North AHB requests a read of a peripheral
on the South AHB. If the AHB/AHB bridge has a free FIFO location, the read request will
be transferred from the master on the North AHB to the AHB/AHB bridge. The AHB/AHB
bridge will complete the read on the South AHB, when it can obtain access to the
peripheral on the South AHB.
Once the AHB/AHB bridge has obtained the read information from the peripheral on the
South AHB, the AHB/AHB bridge notifies the arbiter, on the North AHB, that the AHB/
AHB bridge has the data for the master that requested the “split” transfer. The master
on the North AHB which requested the split transfer will arbitrate for the North AHB and
transfer the read data from the AHB/AHB bridge. The North AHB is released to
complete another transaction while the North AHB master that requested the “split”
transfer waits for the data to arrive.
These “posting” and “splitting” transfers allow control of the North AHB to be given to
another master on the North AHB — enabling the North AHB to achieve maximum
efficiency. Transfers to the AHB/AHB bridge are assumed to be small and infrequent,
relative to the traffic passed between the NPEs on the North AHB and the DDRI SDRAM.
Arbitration on the North AHB is round-robin. Each transaction can be no longer than an
eight-word bursts. This implementation promotes fairness within the system.
2.1.2.2
South AHB
The South AHB is a 133.32-MHz, 32-bit bus that can be mastered by the Intel XScale
®
Processor, PCI controller, Expansion Bus Interface, USB Host Controller, and the AHB/
AHB bridge. The targets of the South AHB Bus can be the DDRI SDRAM, PCI Controller,
Queue Manager, Expansion Bus, Cryptography Unit, or the AHB/APB bridge.
Accessing across the APB/AHB bridge allows interfacing to peripherals attached to the
APB. The Expansion bus is the only target on the South AHB Bus that can be configured
to support split transfers.
Arbitration on the South AHB is round-robin. Each transaction can be no longer than an
eight-word bursts. This implementation promotes fairness within the system.
2.1.2.3
Memory Port Interface
The Memory Port Interface provides a dedicated interface between Intel XScale
®
Processor to the DDRI SDRAM. The Memory Port Interface operates at 133 MHz. This
implementation will allow a theoretical maximum bus bandwidth of over 1 GBps
performance.
The Memory Port Interface stores memory transactions from the Intel XScale processor
which have not been processed by the Memory Controller. The Memory Port Interface
supports eight Intel XScale processor read transactions up to 32 bytes each. That total
equals the maximum number of outstanding transaction the Processor Bus Controller
can support (That includes core DCU [4 - load requests to unique cache lines], IFU [2 -
prefetch], IMM [1 - tablewalk], DMM [1 - tablewalk].)
The Memory Port Interface also supports eight Intel XScale processor-posted write
transactions up to 16 bytes each.
Arbitration on the Memory Port Interface is not required due to no contention with
other masters. Arbitration will exist in the DDRI memory controller between all of the
main internal interfaces.