Digital I/O (MX-4)

Overview⚓︎

Different parts of this list are available depending on the platform. Please consult the technical specification to find the supported IOs.

List of IOs⚓︎

digital-out-1-source
digital-out-2-source
digital-out-3-source
digital-out-4-source
digital-out-5-source
digital-out-6-sink
digital-out-7-sink
digital-out-1-sink
digital-out-2-sink
digital-out-3-sink
digital-out-4-sink
digital-out-5-sink
digital-out-6-source
digital-out-7-source
digital-out-1
- deprecated with digital out source 1
digital-out-2
- deprecated with digital out source 2
digital-out-3
- deprecated with digital out source 3
digital-out-4
- deprecated with digital out source 4
digital-out-5 / 4-20
- deprecated with digital out source 5
digital-out-6
- deprecated with digital out sink 6
digital-in-1 / sc
digital-in-2 / sc
digital-in-3 / sc
digital-in-4 / sc
digital-in-5 / sc
digital-in-6
digital-in-7
digital-in-8
digital-out-7
- depricated with digital out sink 7
digital-out-8
- depricated with digital out source 7
digital-out-en
- Only CT and CT GL

Set Digital out⚓︎

gpioset $(gpiofind digital-out-1)=1

Read Digital in⚓︎

gpioget $(gpiofind digital-in-1)

Systems without gpiolib⚓︎

Note: This is for BSP releases 1.6/1.5 and older

For digital I/O we use the standard linux framework.

See Linux Kernel GPIO documentation

Note: GPIO numbers can differ depending on the exact MX-4 platform. This is just an example.

root@mx4-t30-29009999:~# cat /sys/kernel/debug/gpio | grep -i digital
GPIOs 344-383, spi/spi0.0, mx4_digitals:
 gpio-344 (digital-out-1       ) out lo
 gpio-345 (digital-out-2       ) out lo
 gpio-346 (digital-out-3       ) out lo
 gpio-347 (digital-out-4       ) out lo
 gpio-348 (digital-out-5 / 4-20) out lo
 gpio-349 (digital-out-6       ) out lo
 gpio-356 (digital-in-1 / sc   ) in  hi
 gpio-357 (digital-in-2 / sc   ) in  hi
 gpio-358 (digital-in-3 / sc   ) in  hi
 gpio-359 (digital-in-4 / sc   ) in  hi
 gpio-360 (digital-in-5 / sc   ) in  lo
 gpio-361 (digital-in-6        ) in  lo
 gpio-380 (digital-in-7        ) in  lo
 gpio-381 (digital-in-8        ) in  lo
 gpio-382 (digital-out-7       ) out lo
 gpio-383 (digital-out-8       ) out lo

sc digital out are inputs indicating short for each output. If a short is detected it goes HIGH (1).

Read GPIO value⚓︎

# Example reading status from Digital-In-2. 0 = LOW, 1 = HIGH
root@mx4-gtt:~# cat /sys/class/gpio/gpio23/value
0

Write GPIO value⚓︎

# Example setting Digital-Out-1 high
root@mx4-gtt:~# echo 1 > /sys/class/gpio/gpio238/value

Set input as interrupt⚓︎

Each digital input can trigger an event on a specific change. The changes are rising, falling or both.

# Trigger an event on rising edge.
root@mx4-gtt:~# echo rising > /sys/class/gpio/gpio23/edge

It is also possible to set falling or both to edge file.

To listen for events you need to run poll(2) <http://man7.org/linux/man-pages/man2/poll.2.html> on the value file of that specific input. See example application <https://github.com/hostmobility/file-poll>.

Example app listening for GPIO events⚓︎

    #include <stdio.h>
    #include <fcntl.h>
    #include <poll.h>

    int main (int argc, char *argv[])
    {
        char* path;
        struct pollfd fds;
        int ret;

        if (argc != 2){
            printf("The file descriptor to listen is needed as first (and only) parameter\n");
            return 1;
        }

        path = argv[1];

        fds.fd = open (path, O_RDONLY);

        if (!fds.fd){
            printf("Unable to open file descriptor\n");
            return 1;
        }

        fds.events = POLLERR | POLLPRI;
        fds.revents = 0;
        printf ("listening for events in:%s\n", path);

        char val;

        while (1){
            read (fds.fd, 0, 0);
            if (poll (&fds, 1, -1) > 0) {
                printf ("event received\n");
            }
        }

        printf ("Finish\n");
        return 0;
    }