GPIO Access Usage

You can access the GPIO pins in two ways:

  • ADB shell
  • Java application

Get GPIO Number

To use a GPIO pin, you need to know its PIN number.

Calculation

GPIO PIN number calculation method: Number = Range Base + Pin Index

  1. Range Base refers to the base value of GPIO ranges.

  2. Pin Index refers to the sorting of the GPIO pins you need to calculate in the corresponding ranges.

Example

  1. Get Range Base:
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# cat /sys/kernel/debug/pinctrl/fe000000.apb4\:pinctrl\@4000-pinctrl-meson/gpio-ranges
GPIO ranges handled:
0: periphs-banks GPIOS [355 - 511] PINS [0 - 156]
  1. Get Pin Index:
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# cat /sys/kernel/debug/pinctrl/fe000000.apb4\:pinctrl\@4000-pinctrl-meson/pins
registered pins: 157
pin 0 (GPIOB_0)  fe000000.apb4:pinctrl@4000
pin 1 (GPIOB_1)  fe000000.apb4:pinctrl@4000
pin 2 (GPIOB_2)  fe000000.apb4:pinctrl@4000
pin 3 (GPIOB_3)  fe000000.apb4:pinctrl@4000
pin 4 (GPIOB_4)  fe000000.apb4:pinctrl@4000
pin 5 (GPIOB_5)  fe000000.apb4:pinctrl@4000
pin 6 (GPIOB_6)  fe000000.apb4:pinctrl@4000
pin 7 (GPIOB_7)  fe000000.apb4:pinctrl@4000
pin 8 (GPIOB_8)  fe000000.apb4:pinctrl@4000
pin 9 (GPIOB_9)  fe000000.apb4:pinctrl@4000
...
pin 109 (GPIOT_18)  fe000000.apb4:pinctrl@4000
pin 110 (GPIOT_19)  fe000000.apb4:pinctrl@4000
...
  1. Calculate Number:

Here is an example for GPIOT_19:

GPIOT_19 = Range Base + Pin Index = 355 + 110 = 465

GPIO Usage

When you get the GPIO number, you can follow the steps below to control it.
Here will take GPIO number 465 as a example.

ADB Shell Commands

  • Request GPIO(GPIOT_19)

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    # echo 465  > /sys/class/gpio/export

  • Configure GPIO(GPIOT_19) as output mode

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    # echo out > /sys/class/gpio/gpio465/direction

  • Set GPIO(GPIOT_19) to high level output

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    # echo 1 >  /sys/class/gpio/gpio465/value

  • Set GPIO(GPIOT_19) to low level output

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    # echo 0 >  /sys/class/gpio/gpio465/value

  • Configure GPIO(GPIOT_19) as input mode

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    # echo in > /sys/class/gpio/gpio465/direction

  • Read the level of GPIO(GPIOT_19)

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    # cat /sys/class/gpio/gpio465/value

  • Release GPIO(GPIOT_19)

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    # echo 465 > /sys/class/gpio/unexport

JAVA Application

  • Get root privileges

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

  • Request GPIO(GPIOT_19)

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    DataOutputStream os = new DataOutputStream(mProcess.getOutputStream());
    os.writeBytes("echo " + 465 + " > /sys/class/gpio/export\n");

  • Configure GPIO(GPIOT_19) as output mode

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    os.writeBytes("echo out > /sys/class/gpio/gpio" + 465 + "/direction\n");

  • Set GPIO(GPIOT_19) to high level output

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    os.writeBytes("echo 1 > /sys/class/gpio/gpio" + 465 + "/value\n");

  • Configure GPIO(GPIOT_19) as input mode

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    os.writeBytes("echo in > /sys/class/gpio/gpio" + 465 + "/direction\n");

  • Read the level of GPIO(GPIOT_19)

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    Runtime runtime = Runtime.getRuntime(); 
    Process process = runtime.exec("cat " + "/sys/class/gpio/gpio" + 465 + "/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 GPIO(GPIOT_19)

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    os.writeBytes("echo " + 465 + " > /sys/class/gpio/unexport\n");
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