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Re: [lwip-users] Raw TCP - PBuf segment not decreasing

From: Sergio R. Caprile
Subject: Re: [lwip-users] Raw TCP - PBuf segment not decreasing
Date: Mon, 18 Mar 2019 16:17:09 -0300
User-agent: Mozilla/5.0 (Windows NT 6.1; rv:60.0) Gecko/20100101 Thunderbird/60.5.3

Well, perhaps TI was short on examples but you can learn from the apps
section and those in the contrib tree.

> I actually didn't quite understand how to use tcp_sent() since [...]

When you open a connection (think you can be a server), you set the
environment to serve it and then setup an argument to be passed by
calling tcp_arg() that depends entirely on you. If you are an http
server, you will alloc some memory structure to handle each connection,
and that will be passed on calls to callback functions.
If you don't need it, you don't use it.

The connection has a pcb that is also different from the listening pcb,
so the connection pcb is passed as an argument to callback functions.

> What you mean by " but remember both must be on the same context" [...]

You git it right.
All RAW API functions must be called from within the same execution
environment (perhaps more proper than 'context'), you can handle
everything on the main loop or some people choose to work only
interrupt-driven using the Ethernet Rx interrupt. Those functions are
not protected for reentrability so you must use them on the same
"thread", whether you have an OS or not. (execution environment...)

Most work requires sending some content in response to a request or an
event. You then put inside the TCP buffer as much as you can send, and
if more is left, then, when tcp_sent() informs you that you can send
more because the other end ACKed, you keep pushing until it is done.
There is the first "intention" to send the contents in some part of your
app, in response to the event or the request, and then the real-life
sending in response to the tcp_sent() callback.
Since you want to send at 2KHz, your "intention" will fire every 500us.
TCP might think otherwise, though.

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