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I'm trying to do some joystick programming. I've done a lot of searching with google and have come up empty.
What I'm basically looking for is to know how to read the value of the joystick axis. I've seen a lot of online posts mentioning a "js.c" example program:
Quote:
There is an example program js.c in the joystick loadable kernel module package <linux/joystick.h>.
However I have not been able to find this "js.c" anywhere. Can anyone point me in the right direction?
Simple Directmedia Layer handles graphics, audio, timers, keyboard, mouse and joysticks. You can also do more flexible audio with SDL_mixer, Import many images with SDL_image, do networking stuff with SDL_net. It is easier API than direct kernel stuff.
The Simple Directmedia layer seems like a good solution, but the linux machine will not have that available, so I think that I will still have to resort to the linux API.
BTW, I know the joystick is working and configured, since I used jstest /dev/input/js0.
I just need to know how to read from js0. All that I am trying to do is to log joystick angles over time. Any ideas?
Not sure if you're still wondering about this but ...
I am also getting into joystick programming on linux - but I think most of the docs are fairly old, as I too found that reference but not the mentioned file - but I do have (in the Linux Kernel Sources)
I should have come back to tell everyone that I figgured out my own solution. This will log joystick positions at about 12Hz. It also uses the curses lib. for printing output to the screen....
compile with..
gcc -o js js.c -lpthread -lncurses
Code:
#include <pthread.h>
#include <sys/timeb.h>
#include <curses.h>
#include <fcntl.h>
#include <linux/joystick.h>
#define NUM_THREADS 3
#define JOY_DEV "/dev/js0"
#define HZ 12
const char FILENAME[] = "./joystickLog.out";
char axisDesc[15][5] = {"X", "Y", "Z", "R", "A", "B", "C", "D", "E", "F", "G", "H", "I" };
char numAxis[20], numButtons[20], value[20][20], timeSec[20], timeMilli[20];
int num_of_axis;
void write_to_log(){
sleep(1);
int cnt;
FILE * daFile;
daFile = fopen(FILENAME, "w+");
// WRITE A HEADER ON THE OUPUT FILE
fprintf(daFile, "#,");
for(cnt = 0; cnt < num_of_axis; cnt++)
if(cnt < num_of_axis -1) fprintf(daFile, "%s,", axisDesc[cnt]);
else fprintf(daFile, "%s", axisDesc[cnt]);
fprintf(daFile, "\r\n");
while(1){
fprintf(daFile, "%s.%s, ", timeSec, timeMilli);
for(cnt = 0; cnt < num_of_axis; cnt++){
if(cnt < num_of_axis -1) fprintf(daFile, "%s, ", value[cnt]);
else fprintf(daFile, "%s ", value[cnt]);
}
fprintf(daFile, "\r\n");
usleep(83333);
}
fprintf(daFile, "%s.%s Len = %d ", timeSec, timeMilli,strlen(timeMilli));
fprintf(daFile, "\r\n");
fflush(daFile);
}
void write_to_screen(){
struct timeb seconds;
int cnt, joy_fd, *axis=NULL, num_of_buttons=0, x;
char *button=NULL, name_of_joystick[80];
struct js_event js;
time_t theTime;
wmove(stdscr, 8, 0);
addstr("Type \"q\" to quit.\n");
if( ( joy_fd = open( JOY_DEV , O_RDONLY)) == -1 ){
wmove(stdscr, 3,0);
addstr( "Couldn't open joystick " );
addstr( JOY_DEV );
wmove(stdscr, 10,0);
while(1)usleep(16666);
}
ioctl( joy_fd, JSIOCGAXES, &num_of_axis ); // GET THE NUMBER OF AXIS ON JS
ioctl( joy_fd, JSIOCGBUTTONS, &num_of_buttons ); // GET THE NUMBER OF BUTTONS ON THE JS
ioctl( joy_fd, JSIOCGNAME(80), &name_of_joystick ); // GET THE NAME OF THE JS
axis = (int *) calloc( num_of_axis, sizeof( int ) );
button = (char *) calloc( num_of_buttons, sizeof( char ) );
sprintf(numAxis, "%d", num_of_axis);
sprintf(numButtons, "%d", num_of_buttons);
wmove(stdscr, 0,0);
addstr("Joystick detected: ");
wmove(stdscr, 0, 19);
addstr(name_of_joystick);
wmove(stdscr, 1, 0);
addstr("Number of axis :");
wmove(stdscr, 1, 19);
addstr(numAxis);
wmove(stdscr, 2, 0);
addstr("Number of buttons:");
wmove (stdscr, 2, 19);
addstr(numButtons);
// CHANGE THE STATUS FLAG OF THE FILE DESCRIPTOR TO NON-BLOCKING MODE
fcntl( joy_fd, F_SETFL, O_NONBLOCK );
while( 1 ){
usleep(16666);
// READ THE JOYSTICK STATE, IT WILL BE RETURNED IN THE JS_EVENT STRUCT
read(joy_fd, &js, sizeof(struct js_event));
// GET THE NUMBER OF SECONDS SINCE EPOCH
ftime(&seconds);
theTime = time(NULL);
sprintf(timeSec, "%d", seconds.time);
sprintf(timeMilli, "%d", seconds.millitm);
// CHECK 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;
}
// ADD LEADING 0'S TO THE MILLISECOND STRING (IF NECESSARY)
char temp[10] = "";
while(strlen(temp) < (3 - strlen(timeMilli)))
strcat(temp, "0");
strcat(temp,timeMilli);
strcpy(timeMilli, temp);
// PRINT THE RESULTS
wmove(stdscr, 4, 0);
for(cnt = 0; cnt < num_of_axis; cnt++)
addstr(" ");
for(cnt = 0; cnt < num_of_axis && cnt < 13; cnt++){
sprintf(value[cnt], "%d", axis[cnt]);
wmove(stdscr, 4, cnt * 10);
addstr(axisDesc[cnt]);
addstr(": ");
wmove(stdscr, 4, (cnt * 10) + 2);
addstr(value[cnt]);
}
wmove(stdscr, 6, 0);
addstr(timeSec);
wmove(stdscr, 6,10);
addstr(".");
wmove(stdscr, 6, 11);
addstr(timeMilli);
wmove(stdscr, 6, 15);
addstr("=");
wmove(stdscr, 6, 17);
addstr(ctime(&theTime));
wmove(stdscr, 10, 0);
refresh();
}
}
void *ThreadProcs(void *threadid){
int thread_id = (int)threadid;
if(thread_id == 0){
write_to_screen();
}
if(thread_id == 1){
// THIS THREAD WILL MAKE THE PROGRAM EXIT
int ch;
nodelay(stdscr, TRUE); // SETUP NON BLOCKING INPUT
while(1) {
if ((ch = getch()) == ERR) usleep(16666); // USER HASN'T RESPONDED
else if( ch == 'q'){
endwin();
exit(0); // QUIT ALL THREADS
}
}
}
if(thread_id == 2){
write_to_log();
}
}
int main(int argc, char *argv[]){
initscr(); // INIT THE SCREEN FOR CURSES
pthread_t threads[NUM_THREADS];
int rc, t;
for(t = 0; t < NUM_THREADS; t++){ // MAKE 2 NEW THREADS
rc = pthread_create(&threads[t], NULL, ThreadProcs, (void *)t);
if (rc){
printf("ERROR; return code from pthread_create() is %d\n", rc);
exit(-1);pthread_exit(NULL);
}
}
for(t = 0; t < NUM_THREADS; t++)
pthread_join(threads[t], NULL); // WAIT FOR THREADS TO EXIT OR IT WILL RACE TO HERE.
endwin();
return 0;
}
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