Hello,
I hope to get some advice on how to debug a problem. I am still
investigating it and my knowledge on Ethernet drivers and lwIP is still
limited.
We have 2 lwIP (2.0.2) RAW servers on a Zynq based board. Each server
can serve only 1 client at a time. Over port 4040 server only receives
and over 4041 it only sends data. Everything works fine if we don't
receive and send simultaneously. Communication over 4041 (Tx port)
stalls at some point. We send and receive at data rates of around 1MB/s,
but over 1Gb network.
Looking at Wireshark (121 is PC, 124 is Zynq) we see a lot of Dup ACKs
before communication stalls. But once it stalls, no traffic is captured
at all. For whole minute nothing is captured, until we close our PC app.
Looking at Lwip memory stats on Zynq nothing unusual is observed. What
is strange though is that when communication stalls, LINK STAT xmit
value is being updated (increased), however TCP STAT xmit is not being
updated at all. Therefore, TCP send buffers are not being emptied and we
are not able to write anything at all. We call tcp_output when
tcp_sndbuf(pcb) < TCP_MSS/2, where TCP_MSS is 1460. We don't use tcp
sent callback at all (is that a problem?), just periodically write to
tcp sndbuf. Other side of communication is alive all the time without
problems.
Any ideas on what this situation with LINK and TCP xmit stats mean? Any
ideas on how to debug this problem further?
Thank you very much,
Nenad
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