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ID# Issue Date Notes


16/07/2021 First DESK release


03/03/2022 DESK 3.0.0 release


04/10/2022 Add libgpiod example

Peripheral GPIOs[edit | edit source]

i.MX6 can handle external pins in many different ways and most of them can be configured as GPIOs. When a pin is set as a GPIO, it is possible to read its value, change its direction or change output value directly from the shell.

Device tree configuration[edit | edit source]

Here below an example of device tree configuration for using the RS-485 GPIOs used on standard DAVE's kit for the AXEL Lite SOM:

From imx6q-sbcx-cb0012.dts:

    leds {
        compatible = "gpio-leds";
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_rs232_485_422_1>;

        rs232_485_422 {
            gpios = <&gpio7 13 GPIO_ACTIVE_HIGH>;
            linux,default-trigger = "default-on";

        rs232_on {
            gpios = <&gpio5 29 GPIO_ACTIVE_LOW>;
            linux,default-trigger = "default-on";

From mx6qdl-sbcx-revb-common.dtsi:

    rs232_485_422 {
        pinctrl_rs232_485_422_1: pinctrl_rs232_485_422_grp-1 {
            fsl,pins = <
                MX6QDL_PAD_GPIO_18__GPIO7_IO13      0x1b0b1 /* UART5_485/232 */
                MX6QDL_PAD_CSI0_DAT11__GPIO5_IO29   0x1b0b1 /* UART5_ON */

Accessing the peripheral[edit | edit source]

Linux messages at boot time[edit | edit source]

With the previous leds configuration for the GPIOs, it is possible to find them on sysfs under /sys/class/leds sub-directory:

root@desk-mx6:~# ls -la /sys/class/leds/
total 0
drwxr-xr-x  2 root root 0 Apr  2  2020 .
drwxr-xr-x 54 root root 0 Apr  2  2020 ..
lrwxrwxrwx  1 root root 0 Apr  2  2020 mmc0:: -> ../../devices/soc0/soc/2100000.aips-bus/2190000.usdhc/leds/mmc0::
lrwxrwxrwx  1 root root 0 Apr  2  2020 mmc1:: -> ../../devices/soc0/soc/2100000.aips-bus/2194000.usdhc/leds/mmc1::
lrwxrwxrwx  1 root root 0 Apr  2  2020 rs232_485_422 -> ../../devices/soc0/leds/leds/rs232_485_422
lrwxrwxrwx  1 root root 0 Apr  2  2020 rs232_on -> ../../devices/soc0/leds/leds/rs232_on

Userspace gpio access[edit | edit source]

Usage with sysfs[edit | edit source]

  • set EIM_D26 (MX6QDL_PAD_EIM_D26__GPIO3_IO26) as output GPIO
    • GPIO3_IO26 => (n-1)*32 + IO = (3-1)*32+26 = 90
root@desk-mx6:~# echo 90 > /sys/class/gpio/export
root@desk-mx6:~# echo out > /sys/class/gpio/gpio90/direction
root@desk-mx6:~# echo 1 > /sys/class/gpio/gpio90/value
  • set EIM_D27 (MX6QDL_PAD_EIM_D27__GPIO3_IO27) as input GPIO
root@desk-mx6:~# echo 91 > /sys/class/gpio/export
root@desk-mx6:~# echo in > /sys/class/gpio/gpio91/direction
root@desk-mx6:~# cat /sys/class/gpio/gpio91/value
Additional information[edit | edit source]

Information about GPIOs usage under sysfs directory

Usage with libgpiod[edit | edit source]

Warning-icon.png sysfs GPIO ABI has been deprecated. See more information here about it. A character device access has to be used, more information here Warning-icon.png

Information about GPIOs library libgpiod - C library and tools - can be found on

libgpiod example[edit | edit source]

It is possible yo cross-compile libgpiod in the target (if the related Yocto package is not available for installation). Once the autoconf-archive package has been installed

dnf install autoconf-archive

it is possible to clone the libgpiod git repository and compile the related sources:

git clone
cd libgpiod 
./ --enable-tools=yes --prefix=/usr/local 
make install

Once installed, the gpio utilities are availabel in the target:

root@desk-mx6:~# gpio
gpiodetect  gpiofind    gpioget     gpioinfo    gpiomon     gpioset
root@desk-mx6:~# gpio
gpio interrupt example[edit | edit source]

If a push button, with proper pull-up, is connected to a GPIO line available - for example using the J33.34 pin available on SBC AXEL Lite WIDE connector - the related GPIO can be used as an interrupt:

  • J33.40 is connected to J10.40 SOM pin
    • J33 connector is the WIDE connector in the AXEL Lite EVK
    • J10 connector is the SO-DIMM connector in the AXEL Lite EVK
    • ALT-5 alternate function for this pin is GPIO1_IO06
  • the corresponding pin number is 0 6
  • gpiomon utility can be used for monitor the pin status and triggering, for example, the falling-edge event:
root@desk-mx6:~# gpiomon --falling-edge 0 6
event: FALLING EDGE offset: 6 timestamp: [     696.463539802]
event: FALLING EDGE offset: 6 timestamp: [     696.643661944]