GPIO

GPIO stands for General Purpose Input/Output. It refers to configurable digital pins on microcontrollers or embedded systems that can act as either inputs or outputs, allowing them to read signals (like button presses) or control devices (like LEDs). They serve as the basic interface for interacting with external hardware.

Axon has 30-pin GPIO header pins which can support multiple interfaces like UART, I2C etc.

Axon GPIOs Header

GPIO number

Function4

Function3

Function2

Function1

PWD/GND

GPIO

Pin#

Pin#

GPIO

PWD/GND

Function1

Function2

Function3

Function4

GPIO number

12V

1

2

GPIO0_B6

UART2_RX_M0(DEBUG)

14

GND

3

4

GPIO0_B5

UART2_TX_M0(DEBUG)

13

5V

5

6

GND

5V

7

8

GND

81

UART1_CTSN_M0

I2C2_SCL_M1

GPIO2_C1

9

10

GPIO2_B6

UART1_RX_M0

I2C5_SCL_M4

78

80

UART1_RTSN_M0

I2C2_SDA_M1

GPIO2_C0

11

12

GPIO2_B7

UART1_TX_M0

I2C5_SDA_M4

79

16

PWM1_M0

GPIO0_C0

13

14

3.3V

GND

15

16

3.3V

56

UART6_TX_M2

SPI1_MISO_M2

I2C7_SCL_M0

GPIO1_D0

17

18

GPIO1_D1

UART6_RX_M2

I2C7_SDA_M0

SPI1_MOSI_M2

57

59

PWM1_M1

UART4_RX_M0

SPI1_CS0_M2

I2C1_SDA_M4

GPIO1_D3

19

20

GPIO1_D2

UART4_TX_M0

I2C1_SCL_M4

SPI1_CLK_M2

PWM0_M1

58

GND

21

22

3.3V

43

GPIO1_B3

23

24

1.8V

GND

25

26

GND

SARADC_4

27

28

SARADC_3

SARADC_1

29

30

SARADC_2

Note

You can find GPIO Number Translation: for Axon.

Before going to configure GPIOs, Need to know some basics:

Let’s take one GPIO2_B6 Pin,

Pin

GPIO

GPIO Number

10

GPIO2_B6

78

  • What is GPIO Pin ? It is a Pin which locates on GPIO Header on Axon. Axon has 30 Pins on GPIO header.

  • What is GPIO Number ? You can get GPIO Number from Axon GPIOs Header Table.

  • What is GPIO Chip Num ? In GPIO2_B6, 2 means GPIO Chip Number.

  • What is GPIO Base Number ? It depends on GPIO Chip Number, For example, GPIOCHIP2 has base number = 64

  • What is GPIO Line ? You can get GPIO Line number by substracting GPIO Base Number from GPIO Number.

How GPIO Pins can be configured ?

GPIO Pins can be configured in many ways. For example, you can write program to function pins according to your requirement or you can simply run command using gpiod Command line and you can also use GPIO Pins as UART or I2C Functionality.

Warning

As mention in table, you can use only one function at a time of GPIO Pin.

Let’s take one GPIO1_D1 Pin, You have 3 Function to use this GPIO Pin. Like, UART, I2C, SPI You can only use any of the above one at a time.

Now, Using sudo gpioinfo, you can figure out which pin is located on which gpiochip and gpio_line.

Note

For GPIO2_B6,

GPIO Pin = 10

GPIO Line = 14 ( GPIO_NUM - GPIO_BASE_NUMBER for CHIP2 ) ( 78 - 64 )

GPIO Chip = 2

    vicharak@vicharak:~$ sudo gpioinfo

    gpiochip2 - 32 lines:
            line   0:      unnamed       unused   input  active-high
            line   1:      unnamed       unused   input  active-high
            line   2:      unnamed       unused   input  active-high
            line   3:      unnamed       unused   input  active-high
            line   4:      unnamed       unused   input  active-high
            line   5:      unnamed       unused   input  active-high
            line   6:      unnamed       unused   input  active-high
            line   7:      unnamed       unused   input  active-high
            line   8:      unnamed       unused   input  active-high
            line   9:      unnamed       unused   input  active-high
            line  10:      unnamed       unused   input  active-high
            line  11:      unnamed       unused   input  active-high
            line  12:      unnamed       unused   input  active-high
            line  13:      unnamed       unused   input  active-high
            line  14:     "PIN_10"       unused   input  active-high
            line  15:     "PIN_12"       unused   input  active-high
            line  16:     "PIN_11"       unused   input  active-high
            line  17:      "PIN_9"       unused   input  active-high
            line  18:      unnamed       unused   input  active-high
            line  19:      unnamed       unused   input  active-high
            line  20:      unnamed       unused   input  active-high
            line  21:      unnamed       unused   input  active-high
            line  22:      unnamed       unused   input  active-high
            line  23:      unnamed       unused   input  active-high
            line  24:      unnamed       unused   input  active-high
            line  25:      unnamed       unused   input  active-high
            line  26:      unnamed       unused   input  active-high
            line  27:      unnamed       unused   input  active-high
            line  28:      unnamed       unused   input  active-high
            line  29:      unnamed       unused   input  active-high
            line  30:      unnamed       unused   input  active-high
            line  31:      unnamed       unused   input  active-high

Note

If It shows gpioinfo not found, you need to install gpiod.

sudo apt update

sudo apt gpiod

Using C Language

Below Program will configure GPIO Header Pin 10 (GPIO_NUM 78) using gpiod library.

Make sure, you have installed libgpiod-dev in Axon.

    sudo apt update
    sudo apt-get install -y libgpiod-dev

This code will high GPIO-Pin 10 for 5 sec and again put it in Low.

#include <stdio.h>
#include <gpiod.h>
#include <unistd.h>

#define GPIO_CHIP "/dev/gpiochip2"  // Specify the correct GPIO chip device
#define GPIO_NUMBER 78             // Global GPIO number
#define GPIO_CHIP_BASE 64          // The base GPIO number for gpiochip2 

int main()
{
    struct gpiod_chip *chip;
    struct gpiod_line *line;
    int ret;
    int gpio_line = GPIO_NUMBER - GPIO_CHIP_BASE;  // Local GPIO line number

    // Open the GPIO chip
    chip = gpiod_chip_open(GPIO_CHIP);
    if (!chip)
    {
        perror("Failed to open GPIO chip");
        return EXIT_FAILURE;
    }

    // Get the GPIO line (based on the offset calculated)
    line = gpiod_chip_get_line(chip, gpio_line);
    if (!line)
    {
        perror("Failed to get GPIO line");
        gpiod_chip_close(chip);
        return EXIT_FAILURE;
    }

    // Request the GPIO line as an output and set the initial value to low (0)
    ret = gpiod_line_request_output(line, "gpioset", 0);
    if (ret < 0)
    {
        perror("Failed to request GPIO line as output");
        gpiod_line_release(line);  // Ensure the line is released in case of error
        gpiod_chip_close(chip);
        return EXIT_FAILURE;
    }

    // Set GPIO line 135 to high (enable)
    printf("Setting GPIO %d to high (enabled)\n", GPIO_NUMBER);
    ret = gpiod_line_set_value(line, 1);  // Set value to 1 (high)
    if (ret < 0)
    {
        perror("Failed to set GPIO value");
        gpiod_line_release(line);
        gpiod_chip_close(chip);
        return EXIT_FAILURE;
    }

    // Sleep for a while to keep the pin enabled (you can modify the delay as needed)
    sleep(5);  // Keep the GPIO high for 5 seconds

    // Optionally: Set GPIO line to low (disable) after sleep
    printf("Disabling GPIO %d (set to low)\n", GPIO_NUMBER);
    gpiod_line_set_value(line, 0);  // Set value to 0 (low)

    // Release the GPIO line and close the GPIO chip
    gpiod_line_release(line);
    gpiod_chip_close(chip);

    return 0;
}

  1. Compile above code using gcc <Code_File_Name.c> -o <Executable_File_Name> -lgpiod

  2. Run executable file using sudo as it requires privileges, sudo ./<Executable_File_Name>

Using gpiod Command Line Tool in Linux

  • Install gpiod Command Line Tool

    sudo apt update
    sudo apt install gpiod

  • gpiodetect - List all GPIO chips present on the system, their names, labels and number of GPIO lines.

  • gpioinfo - List all lines of specified GPIO chips, their names, consumers, direction, active state and additional flags.

  • gpioget - Read values of specified GPIO lines.

  • gpioset - Set values of specified GPIO lines, and potentially keep the lines exported and wait until timeout, user input or signal.

Note

For GPIO2_B6, To set GPIO as High X=1 and Low X=0,

sudo gpioset gpiochip2 14=<X>

where, 14 is GPIO Line ( 78 - 64 )

  • gpiofind - Find the GPIO chip name and line offset given the line name.

  • gpiomon - Wait for events on GPIO lines, specifying which events to watch, how many events to process before exiting or if the events should be reported to the console.

How to change Functionality of GPIO Pin Like, UART, I2C etc ?

For that, we will soon provide overlay, on vicharak-config.

See also

https://en.wikipedia.org/wiki/General-purpose_input/output