How To Access GPIO

This guide is about how to access the GPIO using Android and Ubuntu.

Preconditions

The ROM must satisfy the following conditions:

* Android M     >= V170603
* Android N     >= V170421
* Ubuntu Server >= V180712
* Ubuntu Mate   >= V180531

How to Get the GPIO Number

You can get the GPIO number from GPIO Banks or Pins. Different versions of kernel will be different.

Linux 3.14 (Android M, N and Ubuntu)

Banks:

# cat /sys/kernel/debug/pinctrl/c1109880.pinmux/gpio-ranges

GPIO ranges handled:
0: banks GPIOS   [155 - 255] PINS [10 - 110]
0: ao-bank GPIOS [145 - 154] PINS [ 0 -   9]

Notice: ao-bank means GPIOAO_X gpios

Pins:

# cat /sys/kernel/debug/pinctrl/c1109880.pinmux/pins
...
pin 5 (GPIOAO_5) 
pin 6 (GPIOAO_6) 
...
pin 28 (GPIOH_2) 
pin 29 (GPIOH_3) 
pin 30 (GPIOH_4) 
pin 31 (GPIOH_5) 
pin 32 (GPIOH_6) 
pin 33 (GPIOH_7) 
pin 34 (GPIOH_8) 
pin 35 (GPIOH_9) 
...

For example, get the number of GPIOH_4, GPIOH_5 and GPIOAO_6.

Number(GPIOH_5)  = bank + pin = 155 - 10 + 31 = 176
Number(GPIOH_4)  = bank + pin = 155 - 10 + 30 = 175
Number(GPIOAO_6) = bank + pin = 145 -  0 +  6 = 151

Linux 4.9 (Android O and Ubuntu)

aobus-banks:
Banks:

root@Khadas:~# cat /sys/kernel/debug/pinctrl/pinctrl@14/gpio-ranges 
GPIO ranges handled:
0: aobus-banks GPIOS [0 - 10] PINS [0 - 10]

Pins:

root@Khadas:~# cat /sys/kernel/debug/pinctrl/pinctrl@14/pins 
registered pins: 11
pin 0 (GPIOAO_0)  pinctrl@14
pin 1 (GPIOAO_1)  pinctrl@14
pin 2 (GPIOAO_2)  pinctrl@14
pin 3 (GPIOAO_3)  pinctrl@14
pin 4 (GPIOAO_4)  pinctrl@14
pin 5 (GPIOAO_5)  pinctrl@14
pin 6 (GPIOAO_6)  pinctrl@14
pin 7 (GPIOAO_7)  pinctrl@14
pin 8 (GPIOAO_8)  pinctrl@14
pin 9 (GPIOAO_9)  pinctrl@14
pin 10 (GPIO_TEST_N)  pinctrl@14

For example, get the number of GPIOAO_6:
Number(GPIOAO_6) = bank + pin = 0 - 0 + 6 = 6

periphs-banks:
Banks:

root@Khadas:~# cat /sys/kernel/debug/pinctrl/pinctrl@4b0/gpio-ranges
GPIO ranges handled:
0: periphs-banks GPIOS [11 - 110] PINS [11 - 110]

Pins:

root@Khadas:~# cat /sys/kernel/debug/pinctrl/pinctrl@4b0/pins 
registered pins: 100
pin 11 (GPIOZ_0)  pinctrl@4b0
pin 12 (GPIOZ_1)  pinctrl@4b0
pin 13 (GPIOZ_2)  pinctrl@4b0
...
pin 27 (GPIOH_0)  pinctrl@4b0
pin 28 (GPIOH_1)  pinctrl@4b0
pin 29 (GPIOH_2)  pinctrl@4b0
pin 30 (GPIOH_3)  pinctrl@4b0
pin 31 (GPIOH_4)  pinctrl@4b0
pin 32 (GPIOH_5)  pinctrl@4b0
pin 33 (GPIOH_6)  pinctrl@4b0
pin 34 (GPIOH_7)  pinctrl@4b0
pin 35 (GPIOH_8)  pinctrl@4b0
pin 36 (GPIOH_9)  pinctrl@4b0
...
pin 81 (GPIODV_21)  pinctrl@4b0
pin 82 (GPIODV_22)  pinctrl@4b0
pin 83 (GPIODV_23)  pinctrl@4b0
pin 84 (GPIODV_24)  pinctrl@4b0
...

For example, get the number of GPIOH_5:
Number(GPIOH_5) = bank + pin = 11 - 11 + 32 = 32

On Android

GPIO List

PIN         GPIO         Number
PIN37       GPIOH5       176
PIN33       GPIOAO6      151

There are two ways to access the GPIO:

ADB Command
Third-Party Applications

ADB command

Connect the VIMs with a wifi adb:
$ adb connect IP_ADDR

Login to the VIMs:
$ adb shell

Get root permision
$ su

Request the gpio(GPIOH5)
$ echo 176  > /sys/class/gpio/export

Config the gpio(GPIOH5) as output
$ echo out > /sys/class/gpio/gpio176/direction

Config the gpio(GPIOH5) as high level output
$ echo 1 >  /sys/class/gpio/gpio176/value

Config the gpio(GPIOH5) as low level output
$ echo 0 >  /sys/class/gpio/gpio176/value

Config the gpio(GPIOH5) as input
$ echo in > /sys/class/gpio/gpio176/direction

Get the gpio(GPIOH5) level
$ cat /sys/class/gpio/gpio176/value

Release the gpio(GPIOH5)
$ echo 176 > /sys/class/gpio/unexport

Third-Party Applications

Get root permision

Process mProcess = Runtime.getRuntime().exec("su");

Request the gpio(GPIOH5)

DataOutputStream os = new DataOutputStream(mProcess.getOutputStream());
os.writeBytes("echo " + 176 + " > /sys/class/gpio/export\n");

Config the gpio(GPIOH5) as high level output

os.writeBytes("echo out > /sys/class/gpio/gpio" + 176 + "/direction\n");
os.writeBytes("echo 1 > /sys/class/gpio/gpio" + 176 + "/value\n");

Config the gpio(GPIOH5) as input
os.writeBytes("echo in > /sys/class/gpio/gpio" + 176 + "/direction\n");

Get the gpio(GPIOH5) level

Runtime runtime = Runtime.getRuntime(); 
Process process = runtime.exec("cat " + "/sys/class/gpio/gpio" + 176 + "/value");  
InputStream is = process.getInputStream(); 
InputStreamReader isr = new InputStreamReader(is); 
BufferedReader br = new BufferedReader(isr); 
String line ; 
while (null != (line = br.readLine())) { 
 return Integer.parseInt(line.trim()); 
}

Release the gpio(GPIOH5)

os.writeBytes("echo " + 176 + " > /sys/class/gpio/unexport\n");

On Ubuntu

GPIO List

Linux-3.14

PIN         GPIO         Number
PIN37       GPIOH5         176
PIN33       GPIOAO6        151

Linux-4.9.40

PIN         GPIO         Number
PIN37       GPIOH5         32
PIN33       GPIOAO6        6

How to access GPIO on Terminal

[Example on linux-3.14]
Request the gpio(GPIOH5)
$ echo 176 > /sys/class/gpio/export

Config the gpio(GPIOH5) as output
$ echo out > /sys/class/gpio/gpio176/direction

Config the gpio(GPIOH5) as high level output
$ echo 1 >  /sys/class/gpio/gpio176/value

Config the gpio(GPIOH5) as low level output
$ echo 0 >  /sys/class/gpio/gpio176/value

Config the gpio(GPIOH5) as input
$ echo in > /sys/class/gpio/gpio176/direction

Get the level of gpio(GPIOH5)
$ cat  /sys/class/gpio/gpio176/value

Release the gpio(GPIOH5)
$ echo 176 > /sys/class/gpio/unexport