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AR# 33251 Design Assistant for PCI Express - Application Note xapp859 Design Does Not Return Completion for Memory Requests with Non-zero Attribute Field

Description

If the host sends a memory read request with the attribute field set to 01, the XAPP859 designreturns a completion with the attribute field set to 00. This causes acompletion timeout at the host. If the attribute field is set to 2'b00 in the original read request packet, then the returned completion is received correctly.

What is the reason for this failure?

Note: This Answer Record is a part of the Xilinx Solution Center for PCI Express (Xilinx Answer 34536).The Xilinx Solution Center for PCI Express is available to address all questions related to PCIe.Whether you arestarting a new design with PCIe or troubleshooting a problem, use the Solution Center for PCIe to guide you to the right information.

Solution

The problem is theXAPP859 design hard codes the attribute value in the completion packet to be 00. This is a problem if the received memory read request has an attribute of 01. The completion needs to have the same attributes as the original request.

If all incoming memory reads have the attribute set to 00,modify the following line in completer_pkt_gen.v to the corresponding value.

localparam ATTR = 2'b00;

Otherwise, modify the design and copy the original attribute from the read request and use it in the returned completion.

Revision History
07/13/2011 - Initial Release

Linked Answer Records

Associated Answer Records

Answer Number Answer Title Version Found Version Resolved
34085 Design Assistant for PCI Express - Hardware Debug N/A N/A
34538 Xilinx Solution Center for PCI Express - Design Assistant N/A N/A

Actions

AR# 33251
Date Created 07/13/2011
Last Updated 12/15/2012
Status Active
Type General Article
Devices
  • Virtex-5 LXT
  • Virtex-5 SXT
IP
  • Endpoint Block Plus Wrapper for PCI Express
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