FPGA Intellectual Property
PCI Express*, Networking and Connectivity, Memory Interfaces, DSP IP, and Video IP
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Slow transfer speeds PCIE Gen3

Honored Contributor II

Hi all, 


I was working on a design using Stratix V Avalon-ST PCIE Hard IP Gen3 and I get quite varying results. With one machine I can get a consistent high speed PCIE Gen3 and managed to get transfers of 6GB/s. The odd thing it is on a machine from HP that officialy has no Gen3, has only Gen2. 


I tried to find another with Gen3. Tried it on two. One only gives Gen2 (the currentspeed bus always says Gen2). The other one gives gen3. Still on both the speed is just unbeliveably slow, we are talking of 9MB/s and down. 


Any ideas what might be going on. Both of these machines claim Gen3 capability. Anyone else had experiences with this? Could there be something like a Gen3 slot that will only work on video cards and nothing else, or perhaps it will give so much priority to a video card that it will refuse to give any credits to some other card on the system? Or perhaps you happen to know of some other odd requirement that some of these PCIE Gen3 systems might have? 


Any ideas?
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Honored Contributor II

6.0GB/s for Gen 3x8 for both read and write seems reasonable.  

For the machine that get a slow throughput, it could be the link was trained to gen3 intially but was later downtrain to lower speed (gen1 & gen2 only). Try minitor currentspeed signal continuously to ensure the link not downtrain. 

Also can try to monitor the LTSSM to ensure the link does not goes to Recovery state too often.
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