RL-ARM User's Guide

Example for Sending Data

This example demonstrates the basic concept of sending a large amount of data using a UDP socket.

• The example sends 64 Kbytes to the remote IP address 192.168.0.100, which is listening on port 1000.
• The UDP socket will be allocated permanently and will not be released when the data is sent.
• The data is sent as a stream of bytes.
• The UDP socket does not wait for acknowledge from the remote peer to ascertain whether the data has been accepted. For this reason, a very simple acknowledge protocol is added to the example. The data will be sent in 512-byte blocks. Upon receiving the packet, the remote peer will send back a simple UDP packet with an acknowledgement. The acknowledgement is simply an index of the received packet starting with 0.

The steps for this example are as follows:

1. Initialize the system and allocate a free UDP Socket and open it for communication:

   #include <RTL.h>
   
   U8 udp_soc;
   U16 bindex;
   BOOL wait_ack;
   
   void main (void) {
     init_TcpNet ();
     udp_soc = udp_get_socket (0, UDP_OPT_SEND_CS | UDP_OPT_CHK_CS, udp_callback);
     udp_open (udp_soc, 0);
     bindex   = 0;
     wait_ack = __FALSE;
   

2. Run the main thread and call the send_data() function from an endless loop:

     while (1) {
       timer_poll ();
       main_TcpNet ();
       send_data ();
     }
   }
   

3. The send_data() function sends UDP Data and waits for acknowledge. Note that the UDP sockets do not support any acknowledgment. The example provides its own acknowledgement.

   void send_data (void) {
     static const U8 rem_IP[4] = {192,168,0,100};
     U8 *sendbuf;
   
     if (wait_ack == __TRUE) {
       return;
     }
     if (bindex < 128) {
       sendbuf = udp_get_buf (512);
       for (i = 0; i < 512; i += 2) {
         sendbuf[i]   = bcount >> 8;
         sendbuf[i+1] = bcount & 0xFF;
       }
       udp_send (udp_soc, rem_IP, 1000, sendbuf, 512);
     }
   }
   

4. When the packet is sent, wait for the remote acknowledge before proceeding with the next data packet. Use the callback listener function to wait for the remote acknowledge.

   U16 udp_callback (U8 socket, U8 *remip, U16 port, U8 *buf, U16 len)  {
     /* This function is called when UDP data has been received. */
   
     if ((len == 2) && (bindex == (buf[0]<<8 | buf[1]))) {
       wait_ack == __FALSE;
     }
     return (0);
   }
   

Note

• The example assumes that the Network Interface Adapter is selected, enabled, and properly configured in the Net_Config.c configuration file.
• If the system runs out of UDP sockets, the application hangs in an endless loop in the system error function with the error code ERR_UDP_ALLOC.