Keil Logo


Information in this article applies to:

  • RL-ARM All Versions

I have started to use the TCP/IP stack of the Real-Time Library and in this context I have the following questions:


  • Do I need to close/abort a TCP/IP socket when the event TCP_STATE_CLOSED is detected?
  • Can I change from client to server mode after the TCP_STATE_CLOSED event is received or do I need to call the function tcp_abort?
  • What is the effect when I use the call tcp_close on a TCP socket that is currently not open? Calling tcp_close does not seem to generate close event?
  • When my server application is closed TCPnet appears to send sync packets every second. What can be the reason for that?


  • The event TCP_EVT_CLOSE is detected when a TCP socket is closed. There is no further action required in your code. However you must wait until the TCP socket is really down before starting a new connection. TCPnet exchanges close packets after the event TCP_EVT_CLOSE is detected and before TCP socket is in idle state (which is reported by the events TCP_STATE_CLOSED or TCP_STATE_LISTEN. You should use the function tcp_get_state() to check the status of the TCP socket.
  • There is no need to call the function tcp_abort, to close a TCP socket, but you must wait until the TCP socket is in the state TCP_STATE_CLOSED or TCP_STATE_LISTEN.
  • A call to the function tcp_close() sends a control packet with flag TCP_FLAG_FIN set. When this packet is acknowledged by the remote peer a socket is considered as closed. TCPnet waits for the acknowledgement from the remote peer and again you should wait until the socket is in the state TCP_STATE_CLOSED or TCP_STATE_LISTEN.
  • When the function tcp_connect() is called, TCPnet starts to send sync packets. When these sync packets are not answered after a number of retries, the TCP/IP connection is reset and the event TCP_EVT_ABORT is generated.

Last Reviewed: Tuesday, January 23, 2007

Did this article provide the answer you needed?
Not Sure
  Arm logo
Important information

This site uses cookies to store information on your computer. By continuing to use our site, you consent to our cookies.

Change Settings

Privacy Policy Update

Arm’s Privacy Policy has been updated. By continuing to use our site, you consent to Arm’s Privacy Policy. Please review our Privacy Policy to learn more about our collection, use and transfers
of your data.