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Altera_Forum's avatar
Altera_Forum
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14 years ago

Data send thru ethernet

Hello, I am trying to do a simple task: I will form an UDP packet in hardware, then I want to move it to Nios, add IP header and send to ethernet. I will split my problem into two parts: ...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
14 years ago

I've checked packet inserter sources. If I understand verilog and that source correctly, there is no UDP checksum calculated (equals 0).

Indeed, RFC 768 says this:

--- Quote Start ---

If the computed checksum is zero, it is transmitted as all ones (the equivalent in one's complement arithmetic). An all zero transmitted checksum value means that the transmitter generated no checksum (for debugging or for higher level protocols that don't care).

--- Quote End ---

This means, that if the checksum is sent 0 (actually 0 complement of one's), then the checksum is always accepted as OK. Basically, for good ethernet solution, the checksum should be added. I can't find proper implementation of UDP checksum calculations anywhere on the net.

Edit:

Yeah, found this line in the description of the udp_payload_inserter:

--- Quote Start ---

The UDP Checksum field is zero'ed as this component does not compute the UDP Checksum.

--- Quote End ---

So only IP header is calculated there.