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PI7C8150B
ASYNCHRONOUS 2-PORT PCI-TO-PCI BRIDGE
ADVANCE INFORMATION
Page 48 of 109
April 2009 – Revision 1.08
The following general ordering guidelines govern transactions crossing PI7C8150B:
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.
5.3
ORDERING RULES
Table 5-1 shows the ordering relationships of all the transactions and refers by number to
the ordering rules that follow.
Table 5-1. Summary of Transaction Ordering
Pass
Posted
Write
Delayed
Read
Request
Delayed
Write
Request
Delayed Read
Completion
Delayed Write
Completion
Posted Write
No
1
Yes
5
Yes
5
Yes
5
Yes
5
Delayed Read Request
No
2
Yes
Delayed Write Request
No
4
Yes
Delayed Read
Completion
No
3
Yes
Delayed Write
Completion
Yes
Note: The superscript accompanying some of the table entries refers to any applicable
ordering rule listed in this section. Many entries are not governed by these ordering rules;
therefore, the implementation can choose whether or not the transactions pass each other.
The entries without superscripts reflect the PI7C8150B’s implementation choices.
The following ordering rules describe the transaction relationships. Each ordering rule is
followed by an explanation, and the ordering rules are referred to by number in Table 5-1.
These ordering rules apply to posted write transactions, delayed write and read requests,
and delayed write and read completion transactions crossing PI7C8150B in the same