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General Purpose Input/Output (GPIO) is a generic pin on a integrated circuit chip whose behavior (including whether it is an input or output pin) can be controlled / programmed by the user at run time.


GPIO pins have no special purpose defined, and usually go unused by default. The idea is that sometimes the system integrator building a full system that uses the chip might find it useful to have a handful of additional digital control lines, and having these available from the chip can save the hassle of having to arrange additional circuitry to provide them.

A GPIO port is a group of GPIO pins (typically 8 GPIO pins) arranged in a group, and treated as a single port.

Accessing the GPIO pins through sysfs with mainline kernel

The GPIO pins can be accessed from user space using sysfs. To enabled this you need the following kernel option enabled: CONFIG_GPIO_SYSFS

Device Drivers  ---> GPIO Support  ---> /sys/class/gpio/... (sysfs interface)

To access a GPIO pin you first need to export it with

echo XX > /sys/class/gpio/export

with XX being the number of the desired pin. To obtain the correct number you have to calculate it from the pin name (like PH18)[1]:

(position of letter in alphabet - 1) * 32 + pin number

E.g for PH18 this would be ( 8 - 1) * 32 + 18 = 224 + 18 = 242 (since 'h' is the 8th letter).

Alternatively, you can read the mapping from debugfs with

cat /sys/kernel/debug/pinctrl/*/pinmux-pins

After you have successfully exported the pin you can access it through /sys/class/gpio/gpio*NUMBER* (in case of PH18 it's /sys/class/gpio/gpio242).

With /sys/class/gpio/gpio*NUMBER*/direction you must set the pin to out or in using

echo "out" > /sys/class/gpio/gpio*NUMBER*/direction

and only then you can read/write the value with /sys/class/gpio/gpio*NUMBER*/value.

When you are done unexport the pin with

echo XX > /sys/class/gpio/unexport

Accessing the GPIO pins through character device with mainline kernel

The sysfs GPIO interface is now deprecated in favor of character devices /dev/gpiochipX

Verify that your system supports it with

ls /dev/gpiochip*

The easiest way to access the pins is with libgpiod and the set of tools it includes.

You can read a pin with

sudo gpioget gpiochip0 XX

where XX is the pin number, calculated the same way as in the sysfs method (see section above).

Set a pin value with

sudo gpioset gpiochip0 XX=value

where value is 0 or 1. Note the value will return to default after gpioset exits. Consult gpioset --help for further options.

Monitor the state of a pin with

sudo gpiomon gpiochip0 XX

You can use gpioinfo to see how the pins are configured, but

 cat /sys/kernel/debug/pinctrl/*/pinmux-pins 

give you also the pin mapping (see section above).

Accessing the GPIO pins through sysfs on sunxi-3.4

This is subject to changing without notice :( Anyway I found this to hold true on 3.4.103:

First you need to make sure that script.bin has some pins designated for gpio or when you load the appropriate module it will complain that no gpio pins are configured in script.bin.

 gpio_used= 1
 gpio_pin_1= port:PE00
 gpio_pin_2= port:PE01
 gpio_pin_3= port:PE02
 gpio_pin_4= port:PE03
 gpio_pin_5= port:PE04
 gpio_pin_6= port:PE05
 gpio_pin_7= port:PE06
 gpio_pin_8= port:PE07
 gpio_pin_9= port:PE08
 gpio_pin_10= port:PE09
 gpio_pin_11= port:PE10
 gpio_pin_12= port:PE11

Reading the FEX tutorial in the section concerning the Port Definitions would allow you to set pull up/down on the input ports.

Next you need to load the appropriate module:

  modprobe gpio-sunxi

Now export the pins

 for A in 1 2 3 4 5 6 7 8 9 10 11 12; do echo "$A" > /sys/class/gpio/export ; done

This should make some links appear in sys/class/gpio/:

 root@headless2:/sys/class/gpio# ls -l
 total 0
 --w------- 1 root root 4096 Jan 10 00:12 export
 lrwxrwxrwx 1 root root    0 Jan 10 00:12 gpio10_pe9 -> ../../devices/platform/gpio-sunxi/gpio/gpio10_pe9/
 lrwxrwxrwx 1 root root    0 Jan 10 00:12 gpio11_pe10 -> ../../devices/platform/gpio-sunxi/gpio/gpio11_pe10/
 lrwxrwxrwx 1 root root    0 Jan 10 00:12 gpio12_pe11 -> ../../devices/platform/gpio-sunxi/gpio/gpio12_pe11/
 lrwxrwxrwx 1 root root    0 Jan 10 00:11 gpio1_pe0 -> ../../devices/platform/gpio-sunxi/gpio/gpio1_pe0/
 lrwxrwxrwx 1 root root    0 Jan 10 00:12 gpio2_pe1 -> ../../devices/platform/gpio-sunxi/gpio/gpio2_pe1/
 lrwxrwxrwx 1 root root    0 Jan 10 00:12 gpio3_pe2 -> ../../devices/platform/gpio-sunxi/gpio/gpio3_pe2/
 lrwxrwxrwx 1 root root    0 Jan 10 00:12 gpio4_pe3 -> ../../devices/platform/gpio-sunxi/gpio/gpio4_pe3/
 lrwxrwxrwx 1 root root    0 Jan 10 00:12 gpio5_pe4 -> ../../devices/platform/gpio-sunxi/gpio/gpio5_pe4/
 lrwxrwxrwx 1 root root    0 Jan 10 00:12 gpio6_pe5 -> ../../devices/platform/gpio-sunxi/gpio/gpio6_pe5/
 lrwxrwxrwx 1 root root    0 Jan 10 00:12 gpio7_pe6 -> ../../devices/platform/gpio-sunxi/gpio/gpio7_pe6/
 lrwxrwxrwx 1 root root    0 Jan 10 00:12 gpio8_pe7 -> ../../devices/platform/gpio-sunxi/gpio/gpio8_pe7/
 lrwxrwxrwx 1 root root    0 Jan 10 00:12 gpio9_pe8 -> ../../devices/platform/gpio-sunxi/gpio/gpio9_pe8/
 lrwxrwxrwx 1 root root    0 Jan 10 00:10 gpiochip1 -> ../../devices/platform/gpio-sunxi/gpio/gpiochip1/
 --w------- 1 root root 4096 Jan 10 00:09 unexport

Set the desired direction

 echo out > /sys/class/gpio/gpio12_pe11/direction

You may now output something

 echo 1 > /sys/class/gpio/gpio12_pe11/value

Reading the kernel documentation on sysfs gpio can be a good reading and will give you ideas on how to use the other features available. Documentation/gpio/sysfs.txt

You need root privileges to do this. If you don't want this, you may try the following:

Add a group gpio and add the desired user to this group. Then add a file /etc/udev/rules.d/97-gpio.rules

# /etc/udev/rules.d/97-gpio.rules
SUBSYSTEM=="gpio*", PROGRAM="/bin/sh -c '\
    chown -R root:gpio /sys/class/gpio && chmod -R 0770 /sys/class/gpio &&\
    chown -R root:gpio /sys/devices/platform/soc && chmod -R 0770 /sys/devices/platform/soc'"

or /etc/udev/rules.d/96-gpio.rules

# /etc/udev/rules.d/96-gpio.rules
SUBSYSTEM=="gpio*", PROGRAM="/bin/sh -c '\
    chown -R root:gpio /sys/class/gpio && chmod -R 0770 /sys/class/gpio &&\
    chown -R root:gpio /sys/devices/platform/sunxi-pinctrl/gpio && chmod -R 0770 /sys/devices/platform/sunxi-pinctrl/gpio'"

Try which rule runs better.

Example: Controlling GPIO on Olimex's A13-OLinuXino (sunxi-3.4)

What do you need:

  • Kernel with CONFIG_GPIO_SUNXI=y If you set the option to m you should take care of loading the module. There was previously SUN4I_GPIO_UGLY option which is now deprecated.
  • bin2fex and fex2bin tools from sunxi-tools.

The Process

  1. Open a console and connect to your A13.
  2. Make a directory in /media: mkdir /media/nanda
  3. Mount the nanda there: mount /dev/nanda /media/nanda
  4. Copy the file /media/nanda/script.bin to your PC. This file configures the A13.
  5. Now we need to make it a text file so we use the bin2fex. On a linux machine go into the directory where you compiled the sunxi-tools and from there type this: ./bin2fex /path/to/script.bin > script.fex This will create a text file named script.fex in your current directory.
  6. Now we need to edit it with a text editor and define the pins that are going to be used for GPIO. Look for a section named "[gpio_para]" if there is no such section (probably there will not be) go to the bottom of the file and add it like this:
  7. [gpio_para]
    gpio_used = 1
    gpio_num = 1
    gpio_pin_1 = port:PE11<1>
    Do you want to use any GPIO at all? 1=yes 0=no
    The number of total gpio ports you want / pins you are using?
    gpio_pin_$Num = PXN<Z>
    Where $Num is the GPIO pin number. starting from 1.
    PXN is the name of the pin you want to use
    Z is pin a output or a input? 0 for input or 1 for output.

    In this example I used pin PE11 which is pin number 12 on the GPIO-2. The PXN names can be found here: TO CHECK: when I used PE11 this pin is part of the [csi0_para] so I went to [csi0_para] and made csi_used = 0 Not sure if this is needed, but I think it is.

  8. Now we need to make the modified fex file back to bin format so again from the directory where you compiled the sunxi-tools: ./fex2bin script.fex > script.bin
  9. Now put back the script.bin on the board and overwrite the old script.bin in /media/nanda
  10. Unmount the /media/nanda: umount /media/nanda
  11. Reboot the A13
  12. Log back in and now if you did everything correct in /sys/devices/virtual/misc/sun4i-gpio/pin you will see "pe11"
  13. If you solder a LED and a resistor to the right pin and ground (for example pin 2) and type: "echo 1 > /sys/devices/virtual/misc/sun4i-gpio/pin/pe11" the LED will light and "echo 0 > /sys/devices/virtual/misc/sun4i-gpio/pin/pe11" will turn it off.

C/C++ program

Lib gpio_lib.h
compiler eclipse c/c++

       #define PNXX   SUNXI_GPN(XX)


       printf("Failed to initialize GPIO\n");
       return -1;


       printf("Failed to config GPIO pin\n");
       return -1;

PNXX: ex.PD01

        printf("Failed to set GPIO pin value\n");
        return -1;




Other stuff

Olimex wrote another article on the subject at

See also


External Links