Hi,
I want to monitor a pin on BBB for interrupt. I chose pin 117 (pin 25 on P9
-> GPIO3_21 = 32*3+21 = 117. I hope that's correct?)
I came across this question on
stackoverflow<http://stackoverflow.com/questions/3021146/poll2-doesnt-empty-the-event-queue>.
And This is my question on
stackoverflow<http://stackoverflow.com/questions/19434157/poll-to-monitor-a-pin-on-beaglebone-black-continuous-output-even-though-pin-n>
I am following this program from
ridgerun<https://developer.ridgerun.com/wiki/index.php/Gpio-int-test.c> and
made minor changes since I want to monitor just one pin and not any other
files. Changes are highlighted in the code below which I am trying to run.
(I have pasted just the main. Rest is the same as the code from the site)
The problem is, when I run the program, it continuously outputs "poll()
GPIO 117 interrupt occurred" even though I haven't connected anything to
that particular pin and I have to do ctrl+C to stop the execution. POLLPRI
does not work and the program prints just ... after every timeout and I
think POLLIN is proper since it is not a priority data.
Where am I going wrong?
I read about potential problems and the program seems to take care of the
below.
1. The poll() doesn't fail.
2. read() is called after every poll() so data should be consumed. ( I
just want the program to notify whenever there is a rising edge saying
there is an event occured. I do not want to read data from pin. but
included this to avoid potential pitfalls)
3. struct pollfd is being reset inside while loop ( memset((void*)fdset, 0,
sizeof(fdset)); )
int main(int argc, char **argv)
{
*struct pollfd fdset[1];*
*int nfds = 1;*
int gpio_fd, timeout, rc;
char *buf[MAX_BUF];
unsigned int gpio;
int len;
if (argc < 2) {
printf("Usage: gpio-int <gpio-pin>\n\n");
printf("Waits for a change in the GPIO pin voltage level or
input on stdin\n");
exit(-1);
}
gpio = atoi(argv[1]);
gpio_export(gpio);
gpio_set_dir(gpio, 0);
gpio_set_edge(gpio, "rising");
gpio_fd = gpio_fd_open(gpio);
timeout = POLL_TIMEOUT;
while (1) {
memset((void*)fdset, 0, sizeof(fdset));
*fdset[0].fd = gpio_fd;
fdset[0].events = POLLIN;*
rc = poll(fdset, nfds, timeout);
if (rc < 0) {
printf("\npoll() failed!\n");
return -1;
}
if (rc == 0) {
printf(".");
}
*if (fdset[0].revents & POLLIN) {
len = read(fdset[0].fd, buf, MAX_BUF);*
printf("\npoll() GPIO %d interrupt occurred\n", gpio);
}
fflush(stdout);
}
gpio_fd_close(gpio_fd);
return 0;
}
Thanks,
sudhir
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