Re: [lwip-users] Raw TCP Client - wait for ACK after each packet causes slowdown

[Sergio R. Caprile]

Not "probably" ;^) Effectively tcp_sent() is called when an ACK arrives. 
That is what the docs say and how TCP works.
No need to do it timely, though.

Perhaps the idea is something like this:

Oh, I need to send something now.
Is there any room ?
        Yes -> Fill as much buffer as I can
        No -> Oops, will try later
I'm done

tcp_sent():
        Is there anything left to be sent ?
                Yes -> Fill as much buffer as I can
                No -> OK, I'm done, let's have some rest
        Return

"try later" can be done by means of your app resources or using 
tcp_poll() callback, depending on your urge and cpu management needs.

you check the room with tcp_sndbuf(), not MSS. If that does not work, 
there is something in the config that is not OK and that is over my 
head. In such a case we should poll one of the wizards.

tcp_output() instructs tcp to hurry up and send now. Otherwise, "he" 
thinks what is best for everyone ("he" knows better) and will send at 
will; probably waiting for the entire buffer to fill, since no one told 
"him" that info was to be treated as urgent.