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Re: [lwip-users] pbuf_alloc failed after sometime at driver side.

From: Slava Zilberfayn
Subject: Re: [lwip-users] pbuf_alloc failed after sometime at driver side.
Date: Wed, 15 Oct 2014 15:54:16 -0500


I'm having some issues with lwip stack, or rather with the system as
whole. At this point I studied the stack relatively well at seems to
work as intended. However I might be still mistaken, so I'm posting

The root of the problems is that sometimes packets are being
lost for no reason. This can happen even if I connect my PC directly
to the lwip device.

When I look at the WireShark trace, it shows as "TCP Previous Segment
not captured". See attachment. It is certainly not just "not captured", as this 
always accompanied by problems on receiving end and netconn_write
takes longer time to be completed. Eventually the packets are
retransmitted, but it could take like 10 seconds, which is not very

I already instrumented the driver (lpc17_emac), and logs confirm that all 
are leaving my device strictly in order. What could be the reason for
router to ignore my packets? I also tried with two different routers and it
is the same. Could the problem be with MAC-PHY link?

Can anybody suggest further steps for debugging?

Thanks, Slava

Attachment: prev-not-received.pcap
Description: Binary data

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