Re: [lwip-users] lwip-users Digest, Vol 143, Issue 18

[Xun Chen]

Hi Sergio,

Thanks for your pointer and patience!

After some debugging and tracking, I found the problem. I am writing to confirm 
the problem is neither in lwip nor the port, but the communication between the 
remote side and my codes, since this is my first try with callback, I didn't 
handle things properly.

Here is what happened (simplified):

The program is like a data pump to convey data to the remote side at 200kb/sec 
rate. On the first call to tcp_write, I write 3000 bytes, so after two packets 
of 1460 bytes, or 2920 bytes, I get an ACK from remote and the tcp_sent 
callback is invoked. At this point, I have only 300 points. Adding the 80 bytes 
from previous tcp_write, 380 bytes are sent out by lwip.

Now the remote side is waiting for the second TCP packets before it ACKs

There is NO second packet since I only use callback to send out data (my 
previous approach that is not relying on callback will work fine here, but it 
eventually gives me problem and I switched to callback approach per your 
suggestion)

Finally the remote side ACK the last odd packet after waiting for 200ms, and 
now I have A LOT of data in queue for tcp_write, so I observe the pause in my 
data stream, this cycle repeats

I don't lose any data, but the GUI is very jerky due to this 200ms pause.

I can work around it with tricks, but maybe you can give me a better pointer on 
how to deal with the problem so that I can get tcp_sent callback in a nice pace 
for smooth data display.

Thanks and have a nice weekend!

Chen

 Date: Fri, 24 Jul 2015 10:58:31 -0300
From: "Sergio R. Caprile"<address@hidden>
To:address@hidden
Subject: Re: [lwip-users] lwip-users Digest, Vol 143, Issue 10
Message-ID:<address@hidden>
Content-Type: text/plain; charset=utf-8

tcp_sent() is called when a frame arrives, your port notices it and
dispatches to lwIP, and it reckons it is a TCP ACK. All your timing woes
depend mainly on your port, as me and many others don't see that in ours
and we all run the same lwIP.