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4–2
Chapter 4: Parameter Settings
System Settings
Stratix V Hard IP for PCI Express
June 2012
Altera Corporation
Port type
Native Endpoint
Root Port
Legacy Endpoint
Specifies the port type. Altera recommends
Native Endpoint
for all new
Endpoint designs. Select
Legacy Endpoint
only when you require I/O
transaction support for compatibility. The
Root Port
and
Legacy
Endpoint
are not available for the Avalon-MM Stratix V Hard IP for PCI
Express.
The Endpoint stores parameters in the Type 0 Configuration Space which
is outlined in
. The Root Port stores parameters in
the Type 1 Configuration Space which is outlined in
Application interface
64-bit Avalon-ST
128-bit Avalon-ST
256-bit Avalon-ST
Specifies the interface between the PCI Express Transaction Layer and
the Application Layer. Refer to
for a
comprehensive list of available link width, interface width, and frequency
combinations.
“Avalon Memory-Mapped System Settings” on page 4–12
to set
the width of the Application Layer interface for the Avalon-MM Stratix V
Hard IP for PCI Express.
RX Buffer credit
allocation -
performance for
received requests
Minimum
Low
Medium
This setting determines the allocation of posted header credits, posted
data credits, non-posted header credits, completion header credits, and
completion data credits in the 16 KByte RX buffer. The 5 settings allow
you to adjust the credit allocation to optimize your system. The credit
allocation for the selected setting displays in the message pane.
, for more information about
optimizing performance. The Flow Control chapter explains how the
RX
credit allocation
and the
Maximum payload size
that you choose affect
the allocation of flow control credits. You can set the
Maximum payload
size
parameter on the
Device
tab.
The
Message
window of the GUI dynamically updates the number of
credits for Posted, Non-Posted Headers and Data, and Completion
Headers and Data as you change this selection.
■
Minimum
–This setting configures the minimum PCIe specification
allowed non-posted and posted request credits, leaving most of the
RX Buffer space for received completion header and data. Select this
option for variations where application logic generates many read
requests and only infrequently receives single requests from the PCIe
link.
■
Low
– This setting configures a slightly larger amount of RX Buffer
space for non-posted and posted request credits, but still dedicates
most of the space for received completion header and data. Select
this option for variations where application logic generates many read
requests and infrequently receives small bursts of requests from the
PCIe link. This option is recommended for typical endpoint
applications where most of the PCIe traffic is generated by a DMA
engine that is located in the endpoint application layer logic.
■
Balanced
–This setting allocates approximately half the RX Buffer
space to received requests and the other half of the RX Buffer space
to received completions. Select this option for variations where the
received requests and received completions are roughly equal.
Table 4–2. System Settings for PCI Express (Part 2 of 4)
Parameter
Value
Description