DESK-MX6UL-L/Peripherals/GPIOs

History
Issue Date	Notes
2021/07/20	First DESK-MX6UL-L release
2022/03/16	DESK-MX6UL-L 3.0.0 release
2023/05/04	DESK-MX6UL-L 4.0.0 release

Peripheral GPIOs

i.MX6UL 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.

There aren't GIO already configured in the AXEL ULite EVK. Here below an example of GPIOs usage in the i.MX6UL standard product SBCLynx

Device tree configuration

Here below an example of device tree configuration for using the RS-485 GPIOs used on standard DAVE's product SBCLynx:

From imx6ul-lynx-som0013.dtsi:

        /* configure uart8/ttymxc7 as rs232 */
        uart8_rs232_config: uart8_rs232 {
                compatible = "gpio-leds";
                pinctrl-names = "default";
                pinctrl-0 = <&pinctrl_uart8_config>;

                status = "disabled";

                gpio113 {
                        gpios = <&gpio4 17 GPIO_ACTIVE_HIGH>;
                        default-state = "on";
                };
                gpio136 {
                        gpios = <&gpio5 8 GPIO_ACTIVE_HIGH>;
                        default-state = "on";
                };
                gpio137 {
                        gpios = <&gpio5 9 GPIO_ACTIVE_HIGH>;
                        default-state = "on";
                };
        };
};

&iomuxc {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_hog_gpios>;

        imx6ul-lynx {

...
...
                pinctrl_uart8_config: uart8grp-config {
                        fsl,pins = <
                                MX6UL_PAD_SNVS_TAMPER8__GPIO5_IO08      0x80000000 /* MPUART0_DEN */
                                MX6UL_PAD_SNVS_TAMPER9__GPIO5_IO09      0x80000000 /* MPUART0_RXEN */
                                MX6UL_PAD_CSI_MCLK__GPIO4_IO17          0x80000000 /* MPUART0_ON */
                        >;
                };

Accessing the peripheral

Linux messages at boot time

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

root@desk-mx6ul-lynx:~# ls -la /sys/class/leds/
total 0
drwxr-xr-x  2 root root 0 Apr  3 15:19 .
drwxr-xr-x 54 root root 0 Apr  3 15:19 ..
lrwxrwxrwx  1 root root 0 Apr  3 15:19 gpio113 -> ../../devices/platform/uart8_rs232/leds/gpio113
lrwxrwxrwx  1 root root 0 Apr  3 15:19 gpio114 -> ../../devices/platform/uart3_rs485/leds/gpio114
lrwxrwxrwx  1 root root 0 Apr  3 15:19 gpio136 -> ../../devices/platform/uart8_rs232/leds/gpio136
lrwxrwxrwx  1 root root 0 Apr  3 15:19 gpio137 -> ../../devices/platform/uart8_rs232/leds/gpio137
lrwxrwxrwx  1 root root 0 Apr  3 15:19 mmc0:: -> ../../devices/platform/soc/2100000.bus/2190000.mmc/leds/mmc0::
lrwxrwxrwx  1 root root 0 Apr  3 15:19 mmc1:: -> ../../devices/platform/soc/2100000.bus/2194000.mmc/leds/mmc1::

Usage with sysfs

• set GPIO1_IO01 (MX6UL_PAD_GPIO1_IO01__GPIO1_IO01) as output GPIO
  • GPIO1_IO01 => (n-1)*32 + IO = (1-1)*32+1 = 1

root@desk-mx6ul-lynx:~# echo 1 > /sys/class/gpio/export
root@desk-mx6ul-lynx:~# echo out > /sys/class/gpio/gpio1/direction
root@desk-mx6ul-lynx:~# echo 1 > /sys/class/gpio/gpio1/value
root@desk-mx6ul-lynx:~#

• set GPIO1_IO02 (echo 1 > /sys/class/gpio/gpio1/value) as input GPIO
  • GPIO1_IO02 => (n-1)*32 + IO = (1-1)*32+1 = 2

root@desk-mx6ul-lynx:~# echo 2 > /sys/class/gpio/export
root@desk-mx6ul-lynx:~# echo in > /sys/class/gpio/gpio2/direction
root@desk-mx6ul-lynx:~# cat /sys/class/gpio/gpio2/value
0

Additional information

Information about GPIOs usage under sysfs directory https://www.kernel.org/doc/Documentation/gpio/sysfs.txt

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

Information about GPIOs library libgpiod - C library and tools - can be found on git.kernel.org

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