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Altera_Forum's avatar
Altera_Forum
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10 years ago

pcie for dummies

Hello to all.

I would need a text on the fundamentals of the PCIe.

I would like to study the concepts of Endpoint, Root, and Protocol.

I'm using the example hip_cvgt_g2_x4_avmm_dma128_1602.qar, downloaded from the altera's site, but I do not understand what should I change in order to read and write on the PCIe my custom data (from other logic FPGA).

Can you help me?

Regards, Luca

12 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    --- Quote Start ---

    This book was very useful for me:

    https://www.mindshare.com/learn/pci_express/books

    --- Quote End ---

    Hi Tricky!

    can you tell me if in a configuration consisting of : Computer (linux) -> PCIe connector-> C5GTdevboard, the read and write commands are made only from the Computer?

    The PCIe is similar to a master slave configuration?
  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    Its been a long time since I worked with PCIe (and I didnt do it in much depth). But yes, iirc, the PC shouldnt receive commands from the dev board, but the dev board does need to respond appropriately to any reads etc.

  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    PCIe is not master/slave. As long as the system is set up correctly the endpoint can master the bus and read/write the PC's memory space, such as main memory.

  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    --- Quote Start ---

    PCIe is not master/slave. As long as the system is set up correctly the endpoint can master the bus and read/write the PC's memory space, such as main memory.

    --- Quote End ---

    I thought that was the case - but I only used it in a simple set up with the dev card only acting as a slave - as a port to a dual port ram between PC and another processor.

    What was difficult was having only an avalon streaming port as the stand alone hard core (not using Qsys) would only provide a streaming output. Here I had to write logic to decode and reply to the packets. Hence the reason for the book.
  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    Yeah, with the streaming interface you have to deal at the TLP level. We're currently using the Avalon-MM flavor of the hard IP block (gen3x4 endpoint) in an Arria 10 GX dev kit plugged into an Intel motherboard running Linux. The Avalon-MM interface relieves you of the TLP details but we're finding that the latency of the MM interface is costing us throughput. We have the endpoint mastering the bus to stream images from a high-speed image sensor into system memory on the PC. We will likely end up going to the streaming interface to try to eliminate a couple dead cycles per burst on the MM interface. Still have a ton to learn about PCIe. We have a PCIe bus analyzer coming in a week or two and that should be very interesting to play with.

  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    I did learn that windows sends all sorts of wierd and wonderful packets to the core. And it really doesnt like it if you dont respond :) (in the same blue way as holding an interrupt high on PCI)

  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    --- Quote Start ---

    Yeah, with the streaming interface you have to deal at the TLP level. We're currently using the Avalon-MM flavor of the hard IP block (gen3x4 endpoint) in an Arria 10 GX dev kit plugged into an Intel motherboard running Linux. The Avalon-MM interface relieves you of the TLP details but we're finding that the latency of the MM interface is costing us throughput. We have the endpoint mastering the bus to stream images from a high-speed image sensor into system memory on the PC. We will likely end up going to the streaming interface to try to eliminate a couple dead cycles per burst on the MM interface. Still have a ton to learn about PCIe. We have a PCIe bus analyzer coming in a week or two and that should be very interesting to play with.

    --- Quote End ---

    Hi rsefton.

    You know where I can find some examples where the dev board (endpoint) writes and reads the ram the computer?

    I use cyclonevgt dev board and PCIe gen2 x4.
  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    --- Quote Start ---

    Hi rsefton.

    You know where I can find some examples where the dev board (endpoint) writes and reads the ram the computer?

    I use cyclonevgt dev board and PCIe gen2 x4.

    --- Quote End ---

    Altera has a reference design that does this:

    https://www.altera.com/content/dam/altera-www/global/en_us/pdfs/literature/an/an456.pdf

    If you look at page 12 of this document there is a list of links to reference designs for different families. There is a Cyclone V GT design in the list.

    Good luck.
  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    I am desperate.

    I can not carry out my project.

    I have to make a PCIe link from cyclone gt dev board to pc linux.

    The board must generate an interrupt ever 100mSEC ,and linux pc must react to interrupt with a DMA request to the board that sends about 64kB data to PC SDRAM.

    CAn you help me?