
Altera Corporation User Guide Version 11.1 7–41
October 2011
Functional Description
Table 7–14 specifies the ordering rules and behavior of the PCI-Avalon
bridge for the Avalon-to-PCI direction. The entries in this table describe
whether a type in a row may pass a type in a column. The table uses the
following terminology: "No" means a type may not pass another type,
"Yes/No" means a type may pass the other type, but does not have to, and
"Yes" means that a type must pass another type to avoid deadlocks.
Table 7–14. Summary of Ordering in the Avalon-to-PCI Direction
PMW DRR DWR DRC DWC
Spec(1) Impl(2) Spec Impl Spec Impl Spec Impl Spec Impl
PMW No
No(3)
Ye s
Ye s (6)
Ye s
No(8)
Ye s Ye s (10) Ye s
N/A(5)
DRR No
No(3)
Yes / No
No(7)
Yes/ No
No(3)
Yes / No Ye s(10) Yes / N o
N/A(5)
DWR No
No(3)
Yes / No
Ye s (6)
Yes/ No
No(3)
Yes / No Ye s(10) Yes / N o
N/A(5)
DRC No
No(4)
Ye s
Ye s (6)
Ye s N o (9) Ye s/ N o Yes /
No(11)
Yes / No
N/A(5)
DWC Yes/ No N/A(5) Ye s N / A (5) Ye s N / A (5) Yes/ No N/A(5) Yes / N o N/ A (5)
Notes to Table 7–14:
(1) Spec refers to the PCI Local Bus Specification, Revision 3.0, published by PCI-SIG.
(2) Impl refers to the implementation of this passing rule in the PCI-Avalon bridge.
(3) PMWs, DRRs, and DWRs will not pass other PMWs or DWRs since a request at the head of the Avalon-to-PCI
Command/Write Data buffer will be handled first before any subsequent requests.
(4) Ordering logic will make sure that PCI-to-Avalon Read Completion data is not indicated as available on the PCI
side until a previous PMW or DWR is issued.
(5) DWCs are never passed through the PCI-Avalon bridge. The PCI-Avalon bridge can only be the target of a
Configuration Write and these are never delayed.
(6) DRRs can be held pending in the pending read logic or the Avalon-to-PCI Bypassable Read Buffer, allowing them
to be passed by PMWs, DWRs, or DRCs.
(7) Avalon-MM requires that all read data be returned in the order requested. It is possible they can complete on PCI
in a different order if there are multiple Avalon-to-PCI Read Response buffers.
(8) PMWs cannot pass I/O Writes or Configuration Writes (DWRs). However, since the PCI-Avalon bridge does treat
I/O Writes or Configuration Writes in a non-posted fashion, the deadlock avoidance required by the PCI
specification is not required.
(9) DRCs cannot pass I/O Writes or Configuration Writes (DWRs). However, since the PCI-Avalon bridge does treat
I/O Writes or Configuration Writes in a non-posted fashion, the deadlock avoidance required by the PCI
specification is not required.
(10) DRCs can be held in the PCI-to-Avalon Read Response buffers, allowing them to be passed by PMWs, DRRs or
DWRs.
(11) If multiple PCI-to-Avalon Read Response buffers are implemented, then one DRC can pass another. Otherwise,
only one delayed read can be in progress at a time.
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