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Altera_Forum's avatar
Altera_Forum
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13 years ago

Altera Offload UDP IP-How to change Minimum Packet Size

Hi,

I'm trying to use Altera UDP Offload IP for my project. But the minimum packet size is 46, the minimum UDP payload is 18 bytes. This is a limitation. If the UDP payload is less than 18 bytes, zeros will be appended into the packet. Can any one help me that what needs to be changed to reduce this minimum packet size? Or why it has to be 18 bytes, which parameter in the verilog files determines this?

Thank you,

David

4 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    13 years ago

    The 46 minimum packet size is due to Ethernet physical medium.

    AFAIK this derives from collision detection requirements, since this is the minimum frame length which guarantees that overlapping frames are discovered.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    13 years ago

    Thank for your reply. The UDP length can be set to a smaller number. The data is actually send by the Ethernet as trailer. So it is ok.

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    13 years ago

    AFAIK the documentation for the `udp_payload_inserter` module states that if user supplies less data over the Avalon, the module will pad the rest and send it as ethernet trailer (zeros).