Re: [lwip-users] Data sending problem over TCP

[Sanchayan]

Hello,

I have a TCP application, basically i am using the TCP Test Tool to send 
data. I have  written the code for my LM3S6965 board, which listens for 
incoming connections on a particular port and takes the data received. This 
data, which is basically a command, which i then send to a module connected 
over a serial port. Till, this point, i have no problems. Now, the module 
responds back. The module's response, i want to send back on the same 
connection. What should i do to achieve this. For this, i do

// this buffer length can vary anything between 25 to 5000 bytes. Rite, now 
though i am sending a few bytes only
tcp_write( pcb, buff, buff_length, 0 );

tcp_output( pcb );

where pcb is the same Protocol Control Buffer which, i had alloted for the 
connection over which i received the data in the first place. I know, i am 
doing something wrong, since tcp_write gives me a written value -8, which is 
not connected, but i cannot figure out, as i can send the data from the TCP 
Test Tool, but the above thing doesn't work. The connection is active all 
the while. So, can someone help me out how i am to send data, for this case.

Also, looking at another lwip reentrancy issue post, has got me worried over 
what i did and am doing, is gonna bring lot of problems later on somehow and 
is there any documentation available on how to use lwip for carrying out 
necessary tasks at the RAW API level, so that i can learn how to use it 
effectively, as whatever i have done till now has been by looking at the 
code examples given with LM3S6965.

Thanks & Best Regards,
Sanchayan Maity.


----- Original Message ----- 
From: "Kieran Mansley" <address@hidden>
To: "Mailing list for lwIP users" <address@hidden>
Sent: Thursday, June 23, 2011 18:48
Subject: Re: [lwip-users] Data sending problem over TCP


> On Thu, 2011-06-23 at 15:10 +0530, Sanchayan wrote:
> > I have attached the wireshark .pcap file. And also a screenshot of
> > wireshark.
>
> That shows that the connection is being rejected by the host you're
> trying to connect to, probably because there is nothing listening on
> that port number.
>
> This should result in the tcp_err() callback being triggered to notify
> you that the connection has failed.  If it had succeeded the connected
> callback that you can pass to tcp_connect() would be called, but I
> notice that you're just giving it NULL instead.  If you take a look in
> doc/rawapi.txt there's a section there on how to use tcp_connect():
>
> - err_t tcp_connect(struct tcp_pcb *pcb, struct ip_addr *ipaddr,
>                    u16_t port, err_t (* connected)(void *arg,
>                                                    struct tcp_pcb
> *tpcb,
>                                                    err_t err));
>
>  Sets up the pcb to connect to the remote host and sends the
>  initial SYN segment which opens the connection.
>
>  The tcp_connect() function returns immediately; it does not wait for
>  the connection to be properly setup. Instead, it will call the
>  function specified as the fourth argument (the "connected" argument)
>  when the connection is established. If the connection could not be
>  properly established, either because the other host refused the
>  connection or because the other host didn't answer, the "err"
>  callback function of this pcb (registered with tcp_err, see below)
>  will be called.
>
>  The tcp_connect() function can return ERR_MEM if no memory is
>  available for enqueueing the SYN segment. If the SYN indeed was
>  enqueued successfully, the tcp_connect() function returns ERR_OK.
>
> Kieran
>
>
> _______________________________________________
> lwip-users mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/lwip-users 



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