[lwip-users] Only able to tcp_write() data once

[Christer Eriksson]

Hello!

I am trying to get LWIP to work in pppos (ppp over serial) mode and communicate with an echo server in a similar fashion to UNIX’s reading and writing to a socket. LWIP is configured close to an embedded system with only minimal features enabled (NO_SYS=1). A USB virtual serial port is used to talk to a simple GSM modem from a PC.

My problem

I am able to connect to a server and tcp_write() data, but only once. I am able to receive data from the response to the initial tcp_write(). As an example I can write “GET / HTTP/1.0\r\n\r\n” and read the index page. However if I connect to an echo server that just replays the message and leaves the connection open I can only write to the socket once. It all looks good from the LWIP perspective (return codes == 0). The echo server received nothing from the second tcp_write though.

What could be the cause of this problem?

Below is  a link to a program that connects to an echo server and sends "Message 1" followed by Message 2 .. 4. Only "Message 1" arrives at the server.

http://modem.vlsi.se/demo.c or https://pastebin.com/gLqqn0Sh

and the log for the program

http://modem.vlsi.se/a_log or https://pastebin.com/DgmcYNAD

lwipopts.h

http://modem.vlsi.se/lwipopts.h or https://pastebin.com/r8rNHCUs

Is the setup wrong?

Best Regards

Christer