APP.OVERLAY: ERROR AND SOLUTION

[Luiz Miranda]

Hello:

I created an app.overlay.
Here it is:

/ {
aliases {
fra_sw = &fra_sw0;
};
fra_sw0: fra_sw0 {
gpios = <&gpio0 0 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
label = "FRA_SWITCH";
};
};

The build returned the following error:
C:/ncs/v3.2.1/zephyr/include/zephyr/device.h:96:41: error: '__device_dts_ord_DT_N_S_fra_sw0_P_gpios_IDX_0_PH_ORD' undeclared here (not in a function)
96 | #define DEVICE_NAME_GET(dev_id) _CONCAT(__device_, dev_id)

I did a lot of research on the internet and created the app.overlay below:

/ {
aliases {
frasw = &fra_sw0;
};
fra_buttons {
compatible = "gpio-keys";
fra_sw0: fra_sw0 {
gpios = <&gpio0 0 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
label = "FRA_SWITCH";
};
};
};

The build returned no errors.

Questions:
- What is the function of the instructions?
fra_buttons {
compatible = "gpio-keys";?
- Is there another way to create the app.overlay, or is the method that didn't produce an error the correct one?

main.c is below:

#include <zephyr/kernel.h>
#include <zephyr/device.h>
#include <zephyr/drivers/gpio.h>
#include <zephyr/sys/printk.h>

#define SW_NODE DT_ALIAS(frasw)

#if !DT_NODE_HAS_STATUS(SW_NODE, okay)
#error "Alias 'frasw' not defined in the devicetree overlay."
#endif

static const struct gpio_dt_spec sw = GPIO_DT_SPEC_GET(SW_NODE, gpios);
static struct gpio_callback sw_cb;

static void sw_pressed_isr(const struct device *dev,
                           struct gpio_callback *cb,
                           uint32_t pins)
{
    ARG_UNUSED(dev);
    ARG_UNUSED(cb);
    ARG_UNUSED(pins);
    printk("FRA: Switch pressed!\n");
}

int main(void)
{
    int ret;

    if (!device_is_ready(sw.port)) {
        printk("ERROR: GPIO device not ready\n");
        return 0;
    }

    ret = gpio_pin_configure_dt(&sw, GPIO_INPUT);
    if (ret) {
        printk("ERROR: gpio_pin_configure_dt failed (%d)\n", ret);
        return 0;
    }

    ret = gpio_pin_interrupt_configure_dt(&sw, GPIO_INT_EDGE_TO_ACTIVE);
    if (ret) {
        printk("ERROR: gpio_pin_interrupt_configure_dt failed (%d)\n", ret);
        return 0;
    }

    gpio_init_callback(&sw_cb, sw_pressed_isr, BIT(sw.pin));
    gpio_add_callback(sw.port, &sw_cb);

    printk("FRA: Switch test started on P0.%02d (ACTIVE_LOW, pull-up).\n", sw.pin);

    while (1) {
        k_sleep(K_SECONDS(1));
    }
}

Best Regards

Luiz Miranda

[SwRa]

Hi Luiz,

fra_buttons {
compatible = "gpio-keys";?

This creates a devicetree node named fra_buttons whose compatible is "gpio-keys". That tells Zephyr: This node is a gpio-keys device (a collection of GPIO-backed buttons) and  a driver for gpio-keys will see this node and allocate a struct device for it, and also parse its child nodes (like fra_sw0) as individual keys.

Inside that node you have:

fra_sw0: fra_sw0 {
gpios = <&gpio0 0 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
label = "FRA_SWITCH";
};

gpios = <&gpio0 0 ...> is a GPIO phandle array that points to GPIO controller gpio0, pin 0, with flags. Because the parent is compatible = "gpio-keys", the gpio-keys binding knows how to interpret this child node and its gpios property.

That combination (a node with a known compatible, plus a gpios property) is what allows the GPIO and gpio-keys drivers to create the internal device objects that GPIO_DT_SPEC_GET() ultimately relies on.

Is there another way to create the app.overlay

Yes, there are other methods as described here: https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/app_dev/config_and_build/hardware/use_gpio_pin_directly.html or https://docs.nordicsemi.com/bundle/ncs-latest/page/zephyr/build/dts/zephyr-user-node.html#gpios . However, the one you have created also should work (second one).

Regards,

Swathy