I'm using 2.1.2, no RTOS, and seeing frequent duplicate ACKs on Wireshark while lwIP is receiving a continuous audio stream. I've seen up to 6 duplicate ACKs but usually it's one or two.
I enabled: #define TCP_OUTPUT_DEBUG LWIP_DBG_ON and here's a section of the output. The second number in each "sending ACK for" line is an addition of mine and is the micro's core timer for an idea of how quickly these are being sent. Each timer count is 13.3ns. tcp_output: sending ACK for 1450257509 3252152102 tcp_output: nothing to send (0) tcp_output: nothing to send (0) tcp_output: sending ACK for 1450260429 3252196160 tcp_output: nothing to send (0) tcp_output: nothing to send (0) tcp_output: sending ACK for 1450261889 3269439860 tcp_output: nothing to send (0) tcp_output: sending ACK for 1450261889 3288290782 tcp_output: nothing to send (0) tcp_output: sending ACK for 1450261889 3288310973 tcp_output: nothing to send (0) tcp_output: nothing to send (0) tcp_output: sending ACK for 1450261889 3325967548 tcp_output: nothing to send (0) tcp_output: nothing to send (0) tcp_output: sending ACK for 1450262782 3333899283 tcp_output: nothing to send (0) 1450261889 was sent 4 times according to this, and there's actually quite a lot of these in the debug output. Is this normal? I've also attached a small section Wireshark trace which does not necessarily match up with the above debug trace as I can't determine what matches up. 192.168.0.120 is lwIP. How does one go about determining what is causing this? The system running lwIP is otherwise quite reliable and will stream the same TCP connection for hours, despite the duplicate ACKs and retransmissions even over my LAN.
trace.pcapng
Description: Binary data
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