Interfacing to the PC Serial Port

/* do_moncmd():
 *  Open a socket and send the command to the specified port of the
 *  specified host.  Wait for a response if necessary.
 *
 *  hostname:
 *      Character string IP address
 *  command_to_monitor:
 *      Character string command destined for target monitor.
 *  portnum:
 *      Port number that the UDP packet is to be sent to.
 */
int
do_moncmd(char *hostname, char *command_to_monitor, short portnum)
{
    int i, lasterr;
    int msglen;
    ulong   inaddr;
    struct  hostent *hp, host_info;
    char    rcvmsg[1024];
    WSADATA WsaData;
    DWORD   tid;
    HANDLE  tHandle;

   if (WSAStartup (0x0101, &WsaData) == SOCKET_ERROR)
        err("WSAStartup Failed");

    targetHost = hostname;

    /* Build the UDP destination address:
     * Accept target name as string or internet dotted-decimal address.
     */
    memset((char *)&targetAddr,0,sizeof(struct sockaddr));
    if ((inaddr = inet_addr(targetHost)) != INADDR_NONE) {
        memcpy((char *)&targetAddr.sin_addr,(char *)&inaddr,sizeof(inaddr));
        host_info.h_name = NULL;
    }
    else {
        hp = gethostbyname(targetHost);
        if (hp == NULL)
            err("gethostbyname failed");
        host_info = *hp;
        memcpy((char *)&targetAddr.sin_addr,hp->h_addr,hp->h_length);
    }
    targetAddr.sin_family = AF_INET;
    targetAddr.sin_port = htons(portnum);

    /* Open the socket: 
     */
    socketFd = socket(AF_INET,SOCK_DGRAM,0);

    if (socketFd == INVALID_SOCKET)
        err("socket failed");

    /* Send the command string to the target:
     */
    msgString = command_to_monitor;
    if (sendto(socketFd,msgString,(int)strlen(msgString)+1,0,
        (struct sockaddr *)&targetAddr,sizeof(targetAddr)) < 0) {
        close(socketFd);
        err("sendto failed");
    }

    /* Now wait for the response:
     */
    while(1) {
        int j;

        /* Wait for incoming message: */
        msglen = sizeof(struct sockaddr);
        i = recvfrom(socketFd,rcvmsg,sizeof(rcvmsg),0,
            (struct sockaddr *)&targetAddr,&msglen);

        if (i == 0) {
            fprintf(stderr,"Connection closed\n");
            close(socketFd);
            exit(EXIT_ERROR);
        }

        /* If size is 1 and 1st byte is 0 assume that's the target */
        /* saying "I'm done". */
        if ((i==1) && (rcvmsg[0] == 0))
            break;

        /* Print the received message: */
        for(j=0;j<i;j++)
            putchar(rcvmsg[j]);
        fflush(stdout);
    }

    close(socketFd);
    return(EXIT_SUCCESS);
}

Okay, Im gonna be honest here, I dont know what WSAStartup() actually does! And yes, Im OK with that! Like the sneaker commercial says, "just do it!"

The do_moncmd() function processes the IP address or the hostname provided on the command line. The function then opens a socket with SOCK_DGRAM , indicating that the socket is for UDP. After the socket is opened, the code can use the functions sendto() and recvfrom() to send and receive UDP packets. The call to sendto() transfers the string on the command line to the server task on the remote target running MicroMonitor. Finally, the while() loop processes the response. Each line received is printed to the console. To support the ability to receive a multiple-line response but still know when the final line has been received, the server in the monitor terminates the message with a single 1-byte packet containing a NULL . The remote moncmd tests for this packet and exits when appropriate.