Difference between revisions of "DESK-MX6-L/Pheripherals/GPIOs"
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Revision as of 10:29, 5 September 2022
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| 03/03/2022 | DESK 3.0.0 release | ||
Contents
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 root@desk-mx6:~#
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 root@desk-mx6:~#
- 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 1 root@desk-mx6:~#
Additional information[edit | edit source]
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
