Ethernet: No data useful on eth_rxd (Arty Board)

Guest #4609245 
Hey guys,

I am experimenting with UDP on my Arty FPGA 
board.(https://reference.digilentinc.com/arty) After some fiddeling the 
transmitting of data to my laptop already works.

My problem now is that the rx_data bus does not seem to give me other 
data than "0000" and "1111". I have also connected the rx_dv to an led 
and I see it blinking so I assume there should be more useful data than 
just these two values on the bus. I am also sure that there are packets 
sent. I see them in wireshark.

Did you guys already have a similar problem and can point me in a 
general direction?

Greetings,
Jonas
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Guest 
Hey Duke,

Thanks for your answer.

I checked it by letting an led light up permanently after a nibble that 
was not "0000" was found.

I have an LED that is connected to rx_dv and that blinks.

I was not aware that chipscope exists. I will try to learn more about it 
and use it, but for now I have implemented a UDP Sender that 
successfully sends data, that I also see in Wireshark. I now have 
connected the rx_dv to tx_en and rxd to txd and update these on 
falling_edge(tx_clk). This successfully bounces back all packets, but 
instead of any data, every nibble is "0000".

I have attached a Wireshark save file of two example packets sent to the 
FPGA and the two answers. The ethernet frame checksum is wrong because I 
set the UDP packet length to 18. I will try to fix this with an 
automated counter, but it should make no difference.
Attached files:
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I have now also debugged it with the Vivado ILA. I have registered a 
trigger to rxd not being "0000" and it never triggers. When I register a 
trigger to rx_dv it triggers normally. This is really weird.

Do you guys have any ideas?

Jonas
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Guest 
Did you use the correct pins for rxd?
How fast is your ethernet?
How fast is your fpga system clock?

Duke
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Thanks a lot for your help.

Yes I used the correct pins. The .xdc comes directly from the vendor. 
But this was a good tip. I checked the pins and saw that the rdx pins 
were declared at OUT in the elaborated design. I do not know why, but I 
declared the rxd port as a buffer instead of a in port in the VHDL. I 
now declared it as an in port and it works like a charm.

I now feel a bit stupid, but also know more about FPGAs. :D

Jonas
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Hi Jonas,

i know its been a while, but is there any chance you could tell me how 
you implemented the Receiving part or where you got it from ?

I've been searching for days and struggle with finding a code the makes 
receiving udp packets possible, i also use the Arty Board at 100MHz and 
send UDP Packets

regards
Waldi
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Guest 
I second that request - if you have UDP VHDL/Verilog code, or found it 
online, can you post the source? I  tried running the Vivado example 
code but it's not designed for Arty.

Thank you,
Rick
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