GPIO

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.

=Overview= 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) : (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).

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 can set the pin to out or in using echo "out" > /sys/class/gpio/gpio*NUMBER*/direction and 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 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_para] gpio_used= 1 gpio_num=12 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 root@headless2:/sys/class/gpio#

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

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
 Open a console and connect to your A13. Make a directory in /media: mkdir /media/nanda Mount the nanda there: mount /dev/nanda /media/nanda Copy the file /media/nanda/script.bin to your PC. This file configures the A13. 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.</li> 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:</li>

<pre class="brush: ini"> [gpio_para] gpio_used = 1 gpio_num = 1 gpio_pin_1 = port:PE11<1>


 * gpio_used
 * Do you want to use any GPIO at all? 1=yes 0=no


 * gpio_num
 * The number of total gpio ports you want / pins your 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: http://linux-sunxi.org/A13-OLinuXino#Expansion_ports. 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.

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</li> Now put back the script.bin on the board and overwrite the old script.bin in /media/nanda</li> Unmount the /media/nanda: umount /media/nanda</li> Reboot the A13</li> Log back in and now if you did everything correct in /sys/devices/virtual/misc/sun4i-gpio/pin you will see "pe11"</li> If you solder a LED and a resistor to the right pin and ground (for example pin 2) http://linux-sunxi.org/images/e/e7/A13-olinuxino-brd.png 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.</li> </ol>

C/C++ program
Lib              gpio_lib.h

compiler         eclipse c/c++

steps:

1)

#define PNXX  SUNXI_GPN(XX) 2)

if(SETUP_OK!=sunxi_gpio_init){ printf("Failed to initialize GPIO\n"); return -1; } 3)

if(SETUP_OK!=sunxi_gpio_set_cfgpin(PNXX,DIRECTION)){ printf("Failed to config GPIO pin\n"); return -1; } PNXX:             ex.PD01

DIRECTION:        OUTPUT,INPUT

4)

if(sunxi_gpio_output(PNXX,LEVEL)){ printf("Failed to set GPIO pin value\n"); return -1; } LEVEL:           HIGH,LOW

5)

sunxi_gpio_cleanup;

Other stuff
Olimex wrote another article on the subject at http://olimex.wordpress.com/2012/10/23/a13-olinuxino-playing-with-gpios/

=See also=
 * JTAG
 * MicroSD Breakout
 * A10/PIO
 * A13/PIO
 * A20/PIO
 * H3/PIO

=References=

=External Links=
 * ALSA Development List
 * Linux Kernel Doc on GPIO
 * LinuxTV GPIO Pins Info
 * GPIO Tutorial
 * Access GPIO from Linux user space