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Re: [lwip-users] Randomly delayed frame (STM32070 package including LwIP

From: stevestrong
Subject: Re: [lwip-users] Randomly delayed frame (STM32070 package including LwIP v1.4.1)
Date: Fri, 4 Jan 2019 09:47:16 -0700 (MST)

Now back again to the original issue.

I upgraded to v2.1.2 and the problem shows now in different form, and less
frequent (only once in 10 refreshes).

It seems that the delayed frame from STM comes when one packet does not get
received by the client (dropped? lost?), at least Wireshark does not see it.
This packet is for sure Tx-ed by the DMA from the buffer, because the OWN
status bit is cleared by the DMA (can be seen from debug log).

The interesting part is that the packet in question is always the same.

The web page in question loads tree object, one is not found, the second is
a 2.6kB GIF file and the third is a 24kB large JPG image.
The issue happens always when the client (PC) requests the GIF file, then
right after that the JPG file, too.
The STM detects the request for GIF, sends the data (+FIN,PSH,ACK) in two
consecutive packets.
Then STM detects the request for JPG, sends two consecutive data packets
(+PSH,ACK), wherein the second packet, which is always 162 bytes long
(despite that the JPG file is much larger - strange), gets lost.
It is always this second smaller packet which (sometimes) gets lost (at
least not detected) and causes obviously the delay.
Other times this packet in the same configuration (as second consecutive
data frame) is received and everything is ok, no delay.

Any idea how can I improve the situation to avoid lost of this packet?

An additional info: the PHY (DM83848) works in 100mbit, half-duplex mode.

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