What is the purpose of defining a port when working with GPIO? And how do you properly do it.

Question

Hello! 
 I have been working through examples lately trying to get the GPIO and PWM to work. But one issue I keep coming up to is how to define pins as input or output, and how to use GPIO pins in general. I see in all the examples they use nodes and define ports and stuff, but honestly I don't understand what this is and why you do it. 
 Suppose I just want a button on a breadboard as input, then make a led light on the same breadboard light up when it's pressed. Do I have to make two devices and use that as parameter when defining the gpio_pin_configure? And what would the flag be? 
 Also, what is the flag parameter. 
 In all older tutorials and examples I notice this wasn't a thing, and it makes it really difficult to follow and learn. 
 Thanks in advance.

Simon · Accepted Answer

Faws said: However, in this example the led on the board, led 2, increases in intensity. But if I hook up a led to pin 18, it decreases in intensity. They seem inverted. Why is this the case? Take a look at this statement in the infocenter-->nRF52 DK--> Buttons and LEDs , which may clear up your confusion: "The LEDs are active low, meaning that writing a logical zero ('0') to the output pin will illuminate the LED" Faws said: I also notice that in the dts file it says that it is ch0-inverted. It seems like this property simply inverts the output, If I ran the program with the following main() (ch0-inverted is present under the pwm0 node in build/zephyr/zephyr.dts) void main(void) { printk("PWM Application has started! "); uint8_t pulse = 0; const struct device *pwm_dev = device_get_binding(PWM_DEVICE_NAME); if (!pwm_dev) { printk("Cannot find %s! ", PWM_DEVICE_NAME); return; } if (pwm_pin_set_usec(pwm_dev, PWM_CH0_PIN, PWM_PERIOD, PWM_PERIOD-10, 0)) { printk("."); } } I got the following output: If I then deleted the ch0-inverted property: //nrf52dk_nrf52832.overlay &pwm0 { ch0-pin = < 18 >; /delete-property/ ch0-inverted; }; The ouput is now inverted: Faws said: If I would want to do this to any of the pins, say pin 3, how would I define this in the overlay device tree? You simply set ch0-pin to pin 3, like this: &pwm0 { ch0-pin = < 3 >; }; Just as an additional note, since you were confused about ports earlier. If you're using e.g. an nRF52840 and would like to use Port 1 (instead of Port 0) and pin3 you would need to set ch0-pin to 32+3=35 Best regards, Simon

What is the purpose of defining a port when working with GPIO? And how do you properly do it.

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