Driving a GPIO pin directly

This user guide shows how to drive a GPIO pin directly. In the development phase of an embedded project, it can be used to collect execution timings or as a debugging tool.

Declaring the GPIO pin 

To declare a GPIO pin node, use a DTS node with nordic,gpio-pins compatible set in the devicetree. If your application does not use the same GPIO instance as used by the node, enable the GPIO port instance required by the GPIO driver.

This DTS content can be introduced in the DTS of your board, application, or overlay file. Pins defined this way can be accessed using devicetree macros.

The following snippet shows the declaration of a GPIO pin node for Pin 2 of GPIO0. The node is labeled as user-dbg-pin. Additionally, the gpio0 instance and gpiote0 are enabled, so the GPIO driver can be built and executed.

/ {
        user_dbg_pin: user-dbg-pin {
                compatible = "nordic,gpio-pins";
                gpios = <&gpio0 2 GPIO_ACTIVE_HIGH>;
                status = "okay";
        };
};

&gpio0 {
        status = "okay";
};

&gpiote0 {
        status = "okay";
};

Using the pin in your application 

To let your application access the declared pins, use the following devicetree macros:

Declare a GPIO struct instance in your application to allow the GPIO driver API to access the pin:

#include <zephyr/drivers/gpio.h>
static const struct gpio_dt_spec pin_dbg =
   GPIO_DT_SPEC_GET_OR(DT_NODELABEL(user_dbg_pin), gpios, {0});

Make sure your application initializes the pin:

   if (pin_dbg.port) {
      gpio_pin_configure_dt(&pin_dbg, GPIO_OUTPUT_INACTIVE);
}

To let your application drive the pin, add the following code where needed:

if (pin_dbg.port) {
   gpio_pin_set_dt(&pin_dbg, 1);
}
...
if (pin_dbg.port) {
   gpio_pin_set_dt(&pin_dbg, 0);
}

The snippets above show an easy way of generating a square wave that reflects your software execution timings and state. Such a plot can be observed using a logic analyzer or an oscilloscope. Additionally, the code rendered through the snippets is dependent on the binding existence if (pin_dbg.port). This means the snippets will be inactive when you build your application without declaring user-dbg-pin. This is an easy way to disable this debugging infrastructure.

Declaring multiple pins 

Multiple pins can be declared in one GPIO property as well.

/ {
        user_dbg_pin: user-dbg-pin {
                compatible = "nordic,gpio-pins";
                gpios = <&gpio0 2 GPIO_ACTIVE_HIGH>, <&gpio0 3 GPIO_ACTIVE_HIGH>;
                gpio-names = "enter", "exit";
                status = "okay";
        };
};

To initialize the defined GPIO pin structures, use the GPIO_DT_SPEC_INST_GET_BY_IDX_OR() macro.

#include <zephyr/drivers/gpio.h>
static const struct gpio_dt_spec pin_dbg0 =
    GPIO_DT_SPEC_GET_BY_IDX_OR(DT_NODELABEL(user_dbg_pin), gpios, 0, {0});
static const struct gpio_dt_spec pin_dbg1 =
        GPIO_DT_SPEC_GET_BY_IDX_OR(DT_NODELABEL(user_dbg_pin), gpios, 1, {0});

The rest of the GPIO pin operations follow the same process in case of declaring a single pin.

Driving a GPIO pin directly

Declaring the GPIO pin

Using the pin in your application

Declaring multiple pins

Declaring the GPIO pin 

Using the pin in your application 

Declaring multiple pins 