Issues with custom board files & simple peripherals.

[Monkeytronics]

I'm bringing up a custom board, working through the peripherals one at a time. Unfortunately, I haven't gotten very far before things started misbehaving. One part of the design will be an RGB status LED, with PWM for colour & intensity. Here's a snippet which should work as far as I can see. I'm able to drive the individual LEDs fine, but the PWM will not work at all. Note - LEDs are active low, if relevant.

Source Code

------------------

#if PWM_TEST == 1
        #define PWM_PERIOD_NS   20000000
        #define PWM_PULSE_NS    10000000
        #define PWM_GREEN       DT_ALIAS(pwmgreen)
        static const struct pwm_dt_spec pwm_green = PWM_DT_SPEC_GET(PWM_GREEN);
#endif

int main() {
#if PWM_TEST == 1
  if (!pwm_is_ready_dt(&pwm_green)) {
                LOG_ERR("Error: PWM device %s is not ready\n", pwm_green.dev->name);
                return 0;
        }

        int err = pwm_set_dt(&pwm_green, PWM_PERIOD_NS, PWM_PULSE_NS);
        if (err) {
                LOG_ERR("Error in pwm_set_dt(), err: %d", err);
                return 0;
        }
#endif
}

DTS

-------

leds {
        compatible = "gpio-leds"; // generic compatible

        ledred: led_red {
            gpios = <&gpio0 0 GPIO_ACTIVE_LOW>;
            label = "Red LED";
        };

        ledgreen: led_green {
            gpios = <&gpio0 2 GPIO_ACTIVE_LOW>;
            label = "Green LED";
        };

        ledblue: led_blue {
            gpios = <&gpio0 1 GPIO_ACTIVE_LOW>;
            label = "Blue LED";
        };

        vccswen: vcc_sw_en {
            gpios = <&gpio0 31 GPIO_ACTIVE_LOW>;
            label = "VCC Switch Enable";
        };
    };

    pwmleds {
        compatible = "pwm-leds";

        pwm_led0: pwm_led_0 {
            pwms = <&pwm0 0 PWM_MSEC(20) PWM_POLARITY_NORMAL>;
        };

        pwm_led1: pwm_led_1 {
            pwms = <&pwm0 1 PWM_MSEC(20) PWM_POLARITY_NORMAL>;
        };

        pwm_led2: pwm_led_2 {
            pwms = <&pwm0 2 PWM_MSEC(20) PWM_POLARITY_NORMAL>;
        };
    };

aliases {

        ledred = &ledred;
        ledgreen = &ledgreen;
        ledblue = &ledblue;
        vccswen = &vccswen;
        pwmled0 = &pwm_led0;
        pwmred = &pwm_led0;
        pwmgreen = &pwm_led2;
        pwmblue = &pwm_led1;
        mode = &button_mode;

        watchdog0 = &wdt0;
    };

 

proj.conf

------------

...

CONFIG_PWM=y

CONFIG_PWM_LOG_LEVEL_DBG=y

CONFIG_LED=y

CONFIG_LED_PWM=y

[Monkeytronics]

Figured it out. It's in the device tree code. I was defining the 3 PWMs as separate PWM instances: I should have defined one PWM with 3 channels like this. 

PRO: Should only need to do this stuff once.

CON: I can't find great documentation for this stuff. Am I missing it? Would appreciate a link.

&pwm0 {
	status = "okay";
	pinctrl-0 = <&pwm0_default>;
	pinctrl-1 = <&pwm0_sleep>;
	pinctrl-names = "default", "sleep";
};

&pinctrl {
	...
	
	pwm0_default: pwm0_default {
		group1 {
			psels = <NRF_PSEL(PWM_OUT0, 0, 0)>,
				<NRF_PSEL(PWM_OUT1, 0, 1)>,
				<NRF_PSEL(PWM_OUT2, 0, 2)>;
		};
	};

	pwm0_sleep: pwm0_sleep {
		group1 {
			psels = <NRF_PSEL(PWM_OUT0, 0, 0)>,
				<NRF_PSEL(PWM_OUT1, 0, 1)>,
				<NRF_PSEL(PWM_OUT2, 0, 2)>;
			low-power-enable;
		};
	};

    ...
}

[Simonr]

Hi

The PWM lesson in our NCS DevAcademy course available here should cover generic PWM usage. If you think anything specific is missing from it, please let me know and I'll chase down further documentation.

Best regards,

Simon

[Monkeytronics]

The dev academy course is great. But it only has a single PWM channel in the example - so didn't address the aspect that was confusing me (I appreciate that it's on me to learn how device tree works though). Is dev academy the only nrf connect specific resource for developers, or would you recommend other resources? It's all a bit new, but I'm keen to read around as much as possible. 

[Simonr]

Hi Al

I see. I guess we don't have any specific coverage of using multiple PWM channels no, and for learning purposes the Devacademy is the best resource we have. Other things to check out:

PWM API: https://docs.nordicsemi.com/bundle/nrfx-apis-latest/page/group_nrf_pwm.html 

Application development in NCS: https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/app_dev.html 

The DevZone blog:  Blogs 

The DevZone NCS project collection:  nRF Connect SDK projects 

These are at least some good starting points to read up on. Let me know if you're looking for anything in specific and I'll try to help you dig it out. There is a lot of documentation, so I understand the confusion  

Best regards,

Simon