UDP -FPGA point to point

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Manav Nair

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Oct 18, 2021, 8:59:26 AM10/18/21
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Hello everyone, I have recently started working on a project using Ethernet in an FPGA and I am using the UDP protocol for communication between the PC and the FPGA.
The communication is happening point to point so I was wondering do I need ARP implementation in my stack or can I just broadcast the message.

I am building a UDP stack but was wondering is ARP a necessary requirement.
Also, the FPGA doesn't have MAC or UDP port so what value should I assign to them before sending. Thank you in advance

Mana

dalai lamah

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Oct 18, 2021, 10:11:46 AM10/18/21
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Un bel giorno Manav Nair digitņ:

> Hello everyone, I have recently started working on a project using
> Ethernet in an FPGA and I am using the UDP protocol for communication
> between the PC and the FPGA. The communication is happening point to
> point so I was wondering do I need ARP implementation in my stack or can
> I just broadcast the message.

If your connection is really point-to-point, i.e. a physical cable that
goes straight from a host to another, you should be ok without ARP. If you
instead have any routing device in the middle (a switch, a wifi access
point etc..), you should implement ARP or you might have problems.

> I am building a UDP stack but was wondering is ARP a necessary
> requirement. Also, the FPGA doesn't have MAC or UDP port so what value
> should I assign to them before sending. Thank you in advance

Again, if you are straight point-to-point you can assign any MAC address,
as long as it is not all zeroes or FFs. Otherwise you should assign a
"real" MAC address, that you can "steal" from any ethernet device that you
are not going to connect on the same network.

--
Fletto i muscoli e sono nel vuoto.

Manav Nair

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Oct 20, 2021, 10:10:52 AM10/20/21
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Ok, thanks for the response.
I still had one question regarding the UDP. Since I don't know the UDP destination port what should I do in that case? How should I send the UDP message from the PC to the FPGA? I am using scapy for sending data.

Richard Damon

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Oct 20, 2021, 8:59:05 PM10/20/21
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One issue is you are mixing up details at different 'layers' of
communication.

UDP is a transport layer protocol while ARP is a link layer.

WIth a direct connection between the PC and the FPGA, you don't really
HAVE a link layer, which is where a MAC address would matter.

The question comes how you will tell the PC stack how to 'address' the
packet to tell it to send it to the FPGA. That might require some hard
wiring in the stack to provide a routing to the FPGA. The FPGA likely
doesn't need to generate anything there, as it can be just fixed in the
driver to it.

As to a UDP port number, that would determine what the FPGA will do with
datagram.

Are ALL datagrams interpreted the same? if so, then it doesn't matter
what port you use. (maybe the datagram has enough details to define this).

Possibly, you want to be able to send datagrams to different 'ports' in
the FPGA to be processed for different purposes, and if you don't need
it now, you may just want to be using a fixed port so you can add others
in the future.
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