pi7c8150b Pericom Semiconductor Corporation, pi7c8150b Datasheet - Page 47

• Manufacturer Part Number: pi7c8150b
• Description: Asynchronous 2-port Pci Bridge
• Manufacturer: Pericom Semiconductor Corporation

06-0044
5.2
GENERAL ORDERING GUIDELINES
Independent transactions on primary and secondary buses have a relationship only when
those transactions cross PI7C8150B.
The following general ordering guidelines govern transactions crossing PI7C8150B:
PI7C8150B does not merge bytes on separate masked write transactions to the same
DWORD address—this optimization is also best implemented in the originating
master.
PI7C8150B does not collapse sequential write transactions to the same address into a
single write transaction—the PCI Local Bus Specification does not permit this
combining of transactions.
The ordering relationship of a transaction with respect to other transactions is
determined when the transaction completes, that is, when a transaction ends with a
termination other than target retry.
Requests terminated with target retry can be accepted and completed in any order with
respect to other transactions that have been terminated with target retry. If the order of
completion of delayed requests is important, the initiator should not start a second
delayed transaction until the first one has been completed. If more than one delayed
transaction is initiated, the initiator should repeat all delayed transaction requests,
using some fairness algorithm. Repeating a delayed transaction cannot be contingent
on completion of another delayed transaction. Otherwise, a deadlock can occur.
Write transactions flowing in one direction have no ordering requirements with respect
to write transactions flowing in the other direction. PI7C8150B can accept posted write
transactions on both interfaces at the same time, as well as initiate posted write
transactions on both interfaces at the same time.
The acceptance of a posted memory write transaction as a target can never be
contingent on the completion of a non-locked, non-posted transaction as a master. This
is true for PI7C8150B and must also be true for other bus agents. Otherwise, a
deadlock can occur.
PI7C8150B accepts posted write transactions, regardless of the state of completion of
any delayed transactions being forwarded across PI7C8150B.
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ASYNCHRONOUS 2-PORT PCI-TO-PCI BRIDGE
APRIL 2006 – Revision 2.02
PI7C8150B