Keep getting garbage value

Question

I am working on a program that takes an axis value from a USB joystick and sends it over TCP. What I did is first get the TCP program working so I can send messages which was working as expected. Then I wrote another program to obtain the values from the joystick and print them to the screen which also worked as expected.

What I have recently attempted was to combine these two separate programs into one so I have a server program and a client program. That is where my problem has begun, I don't get any errors during compile. It seems that the program is no longer obtaining values from the joystick any longer and storing them in a variable axis[0].

Right now my process is to start the server.c file on the computer with the joystick attached. Then I will start the client.c file on the computer that is supposed to receive the values. I have several printf statements along the way to tell me where the script has gotten to so far. When I execute the server.c script it tells me the joystick is detected and had 6 axis and 12 buttons. It will then wait in a loop until a connection from the client is attempted.

Once the client.c program is executed it will print out the The value is -1093458243. Below that it will print out Incoming connection from 192.168.254.15 - sending welcome. The client program then quits and that is all that happens.

The line that says The value is: should be a number between -32768 and 32767. So it is getting a garbage value from somewhere. I am lost and have been trying to troubleshoot this for an entire day now with no luck. I have included several code examples, the working TCP server and client scripts along with the working joystick script with the code I have tried combining the two with. Can anyone spot any errors in my code, or give me some pointers?

Here is the combined code for server.c:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>

//joysick libraries
#include <sys/ioctl.h>
#include <stdio.h>
#include <fcntl.h>
#include <linux/joystick.h>

//Joysick device
#define JOY_DEV "/dev/input/js0"

//TCP Port number
#define PORTNUM 2343

int main(int argc, char *argv[])
{

//TCP connect
    struct sockaddr_in dest; /* socket info about the machine connecting to us */
    struct sockaddr_in serv; /* socket info about our server */
    int mysocket;            /* socket used to listen for incoming connections */
    socklen_t socksize = sizeof(struct sockaddr_in);

    memset(&serv, 0, sizeof(serv));           /* zero the struct before filling the fields */
    serv.sin_family = AF_INET;                /* set the type of connection to TCP/IP */
    serv.sin_addr.s_addr = htonl(INADDR_ANY); /* set our address to any interface */
    serv.sin_port = htons(PORTNUM);           /* set the server port number */    

    mysocket = socket(AF_INET, SOCK_STREAM, 0);

    /* bind serv information to mysocket */
    bind(mysocket, (struct sockaddr *)&serv, sizeof(struct sockaddr));

    /* start listening, allowing a queue of up to 1 pending connection */
    listen(mysocket, 1);
    int consocket = accept(mysocket, (struct sockaddr *)&dest, &socksize);

//TCP variable
         char msg1[10];


//Joystick variables
        int xAxis;
    int yAxis;
        int xSpeed;
        int ySpeed;

//Joystick initialize
    int joy_fd, *axis=NULL, num_of_axis=0, num_of_buttons=0, x;
    char *button=NULL, name_of_joystick[80];
    struct js_event js;

    if( ( joy_fd = open( JOY_DEV , O_RDONLY)) == -1 )
    {
        printf( "Couldn't open joystick\n" );
        return -1;
    }

//Get number of axes, buttons and name of joystick. Print results to screen
        ioctl( joy_fd, JSIOCGAXES, &num_of_axis );
    ioctl( joy_fd, JSIOCGBUTTONS, &num_of_buttons );
    ioctl( joy_fd, JSIOCGNAME(80), &name_of_joystick );

    axis = (int *) calloc( num_of_axis, sizeof( int ) );
    button = (char *) calloc( num_of_buttons, sizeof( char ) );

    printf("Joystick detected: %s\n\t%d axis\n\t%d buttons\n\n"
        , name_of_joystick
        , num_of_axis
        , num_of_buttons );

//Use non blocking mode for joystick
    fcntl( joy_fd, F_SETFL, O_NONBLOCK );   /* use non-blocking mode */


    while(1) {
//Test to read joystick state
            /* read the joystick state */
        read(joy_fd, &js, sizeof(struct js_event));

            /* see what to do with the event */
        switch (js.type & ~JS_EVENT_INIT)
        {
            case JS_EVENT_AXIS:
                axis   [ js.number ] = js.value;
                break;
            case JS_EVENT_BUTTON:
                button [ js.number ] = js.value;
                break;
        }
//Give msg1 variable the value of axis[0]
    sprintf(msg1, "%d", axis[0]);

    //char msg1 = axis[0];
//TCP send
    while(consocket)
    {
    printf("Value is: %6d\n", axis[0]);
        printf("Incoming connection from %s - sending welcome\n", inet_ntoa(dest.sin_addr));
        send(consocket, msg1, strlen(msg1), 0); 
        consocket = accept(mysocket, (struct sockaddr *)&dest, &socksize);
    }

    close(consocket);
    close(mysocket);
    return EXIT_SUCCESS;

//Print joystick state to screen
    printf("Value is: %d", axis[0]);
    //printf(" \r");
    //fflush(stdout);   
    }


//Joystick close
    close( joy_fd );    /* too bad we never get here */
    return 0;

//TCP message
    //printf("Please enter info\n");
    //fgets(msg1, 20, stdin);

}

Here is the old working server.c file:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>

#define PORTNUM 2343

int main(int argc, char *argv[])
{
    char msg1[] = "Hello World !\n";

    struct sockaddr_in dest; /* socket info about the machine connecting to us */
    struct sockaddr_in serv; /* socket info about our server */
    int mysocket;            /* socket used to listen for incoming connections */
    socklen_t socksize = sizeof(struct sockaddr_in);

    memset(&serv, 0, sizeof(serv));           /* zero the struct before filling the fields */
    serv.sin_family = AF_INET;                /* set the type of connection to TCP/IP */
    serv.sin_addr.s_addr = htonl(INADDR_ANY); /* set our address to any interface */
    serv.sin_port = htons(PORTNUM);           /* set the server port number */    

    mysocket = socket(AF_INET, SOCK_STREAM, 0);

    /* bind serv information to mysocket */
    bind(mysocket, (struct sockaddr *)&serv, sizeof(struct sockaddr));

    /* start listening, allowing a queue of up to 1 pending connection */
    listen(mysocket, 1);
    int consocket = accept(mysocket, (struct sockaddr *)&dest, &socksize);

    while(consocket)
    {
        printf("Incoming connection from %s - sending welcome\n", inet_ntoa(dest.sin_addr));
        send(consocket, msg1, strlen(msg1), 0); 
        consocket = accept(mysocket, (struct sockaddr *)&dest, &socksize);
    }

    close(consocket);
    close(mysocket);
    return EXIT_SUCCESS;
}

Here is the client.c file:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>

#define MAXRCVLEN 500
#define PORTNUM 2343

int main(int argc, char *argv[])
{
   char buffer[MAXRCVLEN + 1]; /* +1 so we can add null terminator */
   int len, mysocket;
   struct sockaddr_in dest; 

   mysocket = socket(AF_INET, SOCK_STREAM, 0);

   memset(&dest, 0, sizeof(dest));                /* zero the struct */
   dest.sin_family = AF_INET;
   dest.sin_addr.s_addr = inet_addr("192.168.254.16"); /* set destination IP number */ 
   dest.sin_port = htons(PORTNUM);                /* set destination port number */

   connect(mysocket, (struct sockaddr *)&dest, sizeof(struct sockaddr));

   len = recv(mysocket, buffer, MAXRCVLEN, 0);

   /* We have to null terminate the received data ourselves */
   buffer[len] = '\0';

   printf("Received %s (%d bytes).\n", buffer, len);

   close(mysocket);
   return EXIT_SUCCESS;
}

This is the joystick file that obtains the values and prints them to the screen:

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/joystick.h>
#include <wiringPi.h>
#define JOY_DEV "/dev/input/js0"

int main()
{
    int xAxis;
    int yAxis;
        int xSpeed;
        int ySpeed;

    FILE *fp;
        fp = fopen("/dev/servoblaster","w");
        if (fp == NULL) {
        printf("Error opening file");
        exit(0);
    }

    int joy_fd, *axis=NULL, num_of_axis=0, num_of_buttons=0, x;
    char *button=NULL, name_of_joystick[80];
    struct js_event js;

    if( ( joy_fd = open( JOY_DEV , O_RDONLY)) == -1 )
    {
        printf( "Couldn't open joystick\n" );
        return -1;
    }

    ioctl( joy_fd, JSIOCGAXES, &num_of_axis );
    ioctl( joy_fd, JSIOCGBUTTONS, &num_of_buttons );
    ioctl( joy_fd, JSIOCGNAME(80), &name_of_joystick );

    axis = (int *) calloc( num_of_axis, sizeof( int ) );
    button = (char *) calloc( num_of_buttons, sizeof( char ) );

    printf("Joystick detected: %s\n\t%d axis\n\t%d buttons\n\n"
        , name_of_joystick
        , num_of_axis
        , num_of_buttons );

    fcntl( joy_fd, F_SETFL, O_NONBLOCK );   /* use non-blocking mode */

    while( 1 )  /* infinite loop */
    {

            /* read the joystick state */
        read(joy_fd, &js, sizeof(struct js_event));

            /* see what to do with the event */
        switch (js.type & ~JS_EVENT_INIT)
        {
            case JS_EVENT_AXIS:
                axis   [ js.number ] = js.value;
                break;
            case JS_EVENT_BUTTON:
                button [ js.number ] = js.value;
                break;
        }

            /* print the results */

        //printf( "X: %6d  Y: %6d  ", axis[0], axis[1] );


        int xAxis = axis[0] / 327;
        int yAxis = axis[1] / 327;
        int ySpeed = 150-0.3*yAxis;
        int xSpeed = 150-0.3*xAxis;
        printf( "X is equal to: %d  Y is equal to: %d  Y speed is: %d ", xAxis, yAxis, ySpeed);

        fprintf(fp, "2=%d\n", ySpeed);
        fprintf(fp, "1=%d\n", xSpeed);
            printf("  \r");
        fflush(stdout);
    }

    close( joy_fd );    /* too bad we never get here */
    return 0;
}

Answer 1

What looks a bit strange to me (and I think it could be a reason of your problems)

fcntl( joy_fd, F_SETFL, O_NONBLOCK );   /* use non-blocking mode */

while( 1 )  /* infinite loop */
{

        /* read the joystick state */
    read(joy_fd, &js, sizeof(struct js_event));

you are using non-blocking mode, but there is no check that read call actually read anything. Since it's non blocking it will return even if no data yet available from joystick device.