Understanding basic button sample code

RE: Understanding basic button sample code

al_ns — Wed, 08 Nov 2023 16:18:55 GMT

Much appreciated Einar! The explanations have help me better understood the button sample code 😄

RE: Understanding basic button sample code

Einar Thorsrud — Wed, 08 Nov 2023 15:14:45 GMT

The difference is that GPIO_DT_SPEC_GET_OR has a default/fallback value which is used if the node and property is not found in the device tree. This makes more sense in generic samples like this which is supposed to work on many different board, and here the LED is optional. In most projects it is not something you would use.

RE: Understanding basic button sample code

al_ns — Wed, 08 Nov 2023 14:21:42 GMT

This is understood.

Next question I have is for:

static const struct gpio_dt_spec button = GPIO_DT_SPEC_GET_OR(SW0_NODE, gpios,
							      {0});

Is there a difference between GPIO_DT_SPEC_GET and GPIO_DT_SPEC_GET_OR?

when do you use which?

RE: Understanding basic button sample code

Einar Thorsrud — Mon, 06 Nov 2023 07:38:04 GMT

It is true (meaning not 0) if led0 exists in the device tree. The reason is is done like this is that a LED is optional in this sample, as you can see from this comment where led is declared:

/*
 * The led0 devicetree alias is optional. If present, we'll use it
 * to turn on the LED whenever the button is pressed.
 */
static struct gpio_dt_spec led = GPIO_DT_SPEC_GET_OR(DT_ALIAS(led0), gpios,
						     {0});

RE: Understanding basic button sample code

al_ns — Sat, 04 Nov 2023 18:09:10 GMT

When is led.port true/1? in the if (led.port)?

RE: Understanding basic button sample code

Einar Thorsrud — Fri, 03 Nov 2023 13:44:37 GMT

Hi,

[quote user=""]Is there a diffence between the above code and #include <zephyr/device.h>? which should be the better choice?[/quote]

This is just form different versions of nRF Connect SDK. With recent versions, you must use #include <zephyr/device.h>.

[quote user=""]May I know if this code is relevant? I assume this is used for unit testing?[/quote]

You can build Zephyr project for many different boards, and as this sample needs a button it is sensible to make sure you get an error if you try to build for a board that does not have a button. You can remove this if you want to.

[quote user=""]This is the first time I have encountered "PRIu32", is this a time data?[/quote]

It is a way to explicitly print a 32 bit unsigned integer.

[quote user=""]What is "led.port->name"? why does it point to name?[/quote]

this comes from the device tree. If you are building for anRF52840 DK, the "name" will be gpio@50000000 because 0x50000000 is the base address for GPIOTE port 0. You can find it in zephyr/dts/arm/nordic/nrf52840.dtsi:

		gpio0: gpio@50000000 {
			compatible = "nordic,nrf-gpio";
			gpio-controller;
			reg = <0x50000000 0x200
			       0x50000500 0x300>;
			#gpio-cells = <2>;
			status = "disabled";
			port = <0>;
		};