How to configure 2 PWM pins with same frequency and duty cycle but opposite polarity

RE: How to configure 2 PWM pins with same frequency and duty cycle but opposite polarity

Susheel Nuguru — Wed, 20 Nov 2024 12:25:36 GMT

I also got it working in a slightly different way, see here

devzone.nordicsemi.com/.../6165.pwm.zip

The trick i used was to use this below in the overlay where I set one pin to inverted

&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, 13)>,
                    <NRF_PSEL(PWM_OUT1, 0, 14)>;
            nordic,drive-mode = <NRF_DRIVE_H0H1>;
        };
    };

    pwm0_sleep: pwm0_sleep {
        group1 {
            psels = <NRF_PSEL(PWM_OUT0, 0, 13)>,
                    <NRF_PSEL(PWM_OUT1, 0, 14)>;
            nordic,drive-mode = <NRF_DRIVE_H0H1>;
        };
    };
};

And in the code I drove both pins same but one should be inverted since it is forced from overlay

   // Configure PWM_OUT0 (normal polarity)
    if (pwm_set(pwm_dev, PWM_CHANNEL0, PWM_PERIOD_USEC, pulse_width, PWM_POLARITY_NORMAL)) {
        printk("Failed to configure PWM channel 0\n");
    } else {
        printk("PWM channel 0 configured: 50%% duty cycle, normal polarity\n");
    }

    // Configure PWM_OUT1 (inverted polarity)
    if (pwm_set(pwm_dev, PWM_CHANNEL1, PWM_PERIOD_USEC, pulse_width, PWM_POLARITY_INVERTED)) {
        printk("Failed to configure PWM channel 1\n");
    } else {
        printk("PWM channel 1 configured: 50%% duty cycle, inverted polarity\n");
    }

I guess there are many ways to do it.

RE: How to configure 2 PWM pins with same frequency and duty cycle but opposite polarity

mkjones — Tue, 19 Nov 2024 19:55:21 GMT

Through much trial-and-error, I finally got it working. First, I gave up on trying to use PWM_DT_SPEC_GET; in the end, I just used the PMW device directly. Also, the other bit of magic which was not obvious was that each channel needs to use a different function (so, PMW_OUT0 and PMW_OUT1 below) So, here's the overlay file:

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

&pinctrl {
    pwm0_default: pwm0_default {
        group1 {
            psels = <NRF_PSEL(PWM_OUT0, 0, 22)>,
                    <NRF_PSEL(PWM_OUT1, 0, 23)>;
            nordic,drive-mode = <NRF_DRIVE_H0H1>;
        };
    };
};

And here's the source file; the final bit of magic was to use PWM_POLARITY_NORMAL for one channel and PWM_POLARITY_INVERTED for the other. Now I get identical (but inverted) waveforms on the two channels:

/** @file speaker.c
 * 
 * Interface to the speaker.
 */
#include "speaker.h"
#include <zephyr/kernel.h>
#include <zephyr/drivers/pwm.h>

#include <zephyr/logging/log.h>
LOG_MODULE_REGISTER(SPKR, LOG_LEVEL_DBG);

// The PWM device (must contain two channels, 0=audio, 1=boost)
const struct device *pwm = DEVICE_DT_GET(DT_NODELABEL(pwm0));

// Channel numbers for the two PWMs
#define AUDIO_CHANNEL   0
#define BOOST_CHANNEL   1

// Frequency to run the speaker at (4.1KHz, 50% duty cycle)
#define SPEAKER_FREQUENCY_HZ    4100
#define SPEAKER_PERIOD          PWM_HZ(SPEAKER_FREQUENCY_HZ)
#define SPEAKER_PULSE           (SPEAKER_PERIOD / 2)

/**
 * @brief Initialize the speaker
 */
int speaker_init()
{
    int err;

    if (!device_is_ready(pwm))
    {
        LOG_ERR("PWM device is not ready");
        err = -ENODEV;
    }
    else
    {
        LOG_INF("PWM initalized");
        err = 0;
    }
    return err;
}

/**
 * @brief Turn the speaker on
 */
int speaker_on()
{
    int err;

    if (!device_is_ready(pwm))
    {
        LOG_ERR("PWM device not ready");
        err = -ENODEV;
    }
    else if ((err = pwm_set(pwm, AUDIO_CHANNEL, SPEAKER_PERIOD, SPEAKER_PULSE, PWM_POLARITY_NORMAL)))
    {
        LOG_ERR("pwm_set audio failed, err=%d", err);
    }
    else if ((err = pwm_set(pwm, BOOST_CHANNEL, SPEAKER_PERIOD, SPEAKER_PULSE, PWM_POLARITY_INVERTED)))
    {
        LOG_ERR("pwm_set boost failed, err=%d", err);
    }
    return err;
}

/**
 * @brief Turn the speaker off
 */
int speaker_off()
{
    int err;

    if (!device_is_ready(pwm))
    {
        LOG_ERR("PWM device not ready");
        err = -ENODEV;
    }
    else if ((err = pwm_set(pwm, AUDIO_CHANNEL, SPEAKER_PERIOD, 0, PWM_POLARITY_NORMAL)))
    {
        LOG_ERR("pwm_set audio failed, err=%d", err);
    }
    else if ((err = pwm_set(pwm, BOOST_CHANNEL, SPEAKER_PERIOD, 0, PWM_POLARITY_NORMAL)))
    {
        LOG_ERR("pwm_set boost failed, err=%d", err);
    }
    return err;
}

RE: How to configure 2 PWM pins with same frequency and duty cycle but opposite polarity

Susheel Nuguru — Tue, 19 Nov 2024 15:36:02 GMT

This should have been a very simple thing, sorry that it is taking this long, i will test this tomorrow on DK, it shouldn't be this difficult to generate an inverted signal on two pins using a PWM.

RE: How to configure 2 PWM pins with same frequency and duty cycle but opposite polarity

mkjones — Mon, 18 Nov 2024 17:46:40 GMT

OK, I've got it to compile (I ended up using C:\ncs\v2.7.0\nrf\samples\bluetooth\fast_pair\locator_tag\ as a model):

/ {
    aliases {
        pwm-spk = &buzzer;
    };

    pwmbuzzer {
        compatible = "pwm-leds";
        status = "okay";

        buzzer: buzzer_pwm {
            pwms =  <&pwm0 0 PWM_HZ(4100) PWM_POLARITY_NORMAL>,
                    <&pwm0 1 PWM_HZ(4100) PWM_POLARITY_INVERTED>;
            label = "PWM_1";
        };
    };
};

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

&pinctrl {
    pwm0_default: pwm0_default {
        group1 {
            psels = <NRF_PSEL(PWM_OUT0, 0, 22)>,
                    <NRF_PSEL(PWM_OUT0, 0, 23)>;
            nordic,drive-mode = <NRF_DRIVE_H0H1>;
        };
    };
};

However, when I execute this function:

int speaker_on()
{
    int err;

    if (!device_is_ready(pwm.dev))
    {
        LOG_ERR("Speaker PWM not ready");
        err = -ENODEV;
    }
    else if ((err = pwm_set(pwm.dev, AUDIO_CHANNEL, SPEAKER_PERIOD, SPEAKER_PULSE, PWM_POLARITY_NORMAL)))
    {
        LOG_ERR("pwm_set audio failed, err=%d", err);
    }
    else if ((err = pwm_set(pwm.dev, BOOST_CHANNEL, SPEAKER_PERIOD, SPEAKER_PULSE, PWM_POLARITY_INVERTED)))
    {
        LOG_ERR("pwm_set boost failed, err=%d", err);
    }
    return err;
}

I only get output from the second channel (GPIO 0.23); GPIO 0.22 just stays low.

RE: How to configure 2 PWM pins with same frequency and duty cycle but opposite polarity

mkjones — Mon, 18 Nov 2024 16:42:56 GMT

The line that will not compile for me is:

const struct pwm_dt_spec pwm = PWM_DT_SPEC_GET(DT_NODELABEL(pwm0));

It clearly does not like the way I've defined my pwm device. I have tried following the two (different) examples:

https://academy.nordicsemi.com/courses/nrf-connect-sdk-intermediate/lessons/lesson-4-pulse-width-modulation-pwm/topic/zephyr-pwm-api/

https://blog.golioth.io/adding-pwm-sound-in-zephyr/

Nothing I do makes the compiler happy. Can you also give me the contents of the .overlay file that will make the code sample you've provided compile?

This is *incredibly* frustrating; the whole DTS thing is certainly powerful, but unless you are already an expert (and I am not), it is virtually impossible to produce code that will compile (never mind work correctly) unless you can find a sample that does exactly what you need.

RE: How to configure 2 PWM pins with same frequency and duty cycle but opposite polarity

Susheel Nuguru — Sun, 17 Nov 2024 11:36:19 GMT

[quote user="mkjones"]Since my duty cycle is 50%, the pulse length for pwm_2 is exactly the same as pmw_1; I don't understand how this gets the opposite polarity.[/quote]

the second channel of the PWM configured with period_usec - duty_cycle_usec, meaning it starts low and becomes high when Channel 0 transitions to low.

The error:'__device_dts_ord_DT_N_S_soc_S_pwm_4001c000_P_pwms_IDX_0_PH_ORD' undeclared

and the code looks something like, not compiled but to show you the logic

#include <zephyr/drivers/pwm.h>

const struct pwm_dt_spec pwm = PWM_DT_SPEC_GET(DT_NODELABEL(pwm0));

void configure_pwm_single_instance(uint32_t period_usec, uint32_t duty_cycle_usec)
{
    if (!device_is_ready(pwm.dev)) {
        printk("Error: PWM device is not ready.\n");
        return;
    }

    int ret = pwm_set(pwm.dev, 0, PWM_USEC(period_usec), PWM_USEC(duty_cycle_usec));
    if (ret) {
        printk("Failed to configure channel 0 (normal polarity): %d\n", ret);
    }

    ret = pwm_set(pwm.dev, 1, PWM_USEC(period_usec), PWM_USEC(period_usec - duty_cycle_usec));
    if (ret) {
        printk("Failed to configure channel 1 (inverted polarity): %d\n", ret);
    }

    printk("PWM configured with complementary signals on a single instance.\n");
}

RE: How to configure 2 PWM pins with same frequency and duty cycle but opposite polarity

mkjones — Fri, 15 Nov 2024 20:37:41 GMT

Here's what I've defined in my overlay file:

pwm0: &pwm0 {
    status = "okay";
    pinctrl-0 = <&pwm0_default>;
    pinctrl-names = "default";
};

&pinctrl {
    pwm0_default: pwm0_default {
        group1 {
            psels = <NRF_PSEL(PWM_OUT0, 0, 22)>,    // Channel 0: Audio PWM
                    <NRF_PSEL(PWM_OUT0, 0, 23)>;    // Channel 1: Boost PWM
            nordic,drive-mode = <NRF_DRIVE_H0H1>;
        };
    };
};

Here's what's at the top my source file:

const struct pwm_dt_spec pwm = PWM_DT_SPEC_GET(DT_NODELABEL(pwm0));

#define AUDIO_CHANNEL   0
#define BOOST_CHANNEL   1

It simply will not compile; it is unable to find pwm0 (I think; it is actually impossible to tell what the build system is unhappy about). Here is the compiler output:

C:/ncs/v2.7.0/zephyr/include/zephyr/device.h:91:41: error: '__device_dts_ord_DT_N_S_soc_S_pwm_4001c000_P_pwms_IDX_0_PH_ORD' undeclared here (not in a function)
   91 | #define DEVICE_NAME_GET(dev_id) _CONCAT(__device_, dev_id)
      |                                         ^~~~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/toolchain/common.h:137:26: note: in definition of macro '_DO_CONCAT'
137 | #define _DO_CONCAT(x, y) x ## y
      |                          ^
C:/ncs/v2.7.0/zephyr/include/zephyr/device.h:91:33: note: in expansion of macro '_CONCAT'
   91 | #define DEVICE_NAME_GET(dev_id) _CONCAT(__device_, dev_id)
      |                                 ^~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/device.h:228:37: note: in expansion of macro 'DEVICE_NAME_GET'
228 | #define DEVICE_DT_NAME_GET(node_id) DEVICE_NAME_GET(Z_DEVICE_DT_DEV_ID(node_id))
      |                                     ^~~~~~~~~~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/device.h:245:34: note: in expansion of macro 'DEVICE_DT_NAME_GET'
245 | #define DEVICE_DT_GET(node_id) (&DEVICE_DT_NAME_GET(node_id))
      |                                  ^~~~~~~~~~~~~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/drivers/pwm.h:260:24: note: in expansion of macro 'DEVICE_DT_GET'
260 |                 .dev = DEVICE_DT_GET(DT_PWMS_CTLR_BY_IDX(node_id, idx)),       \
      |                        ^~~~~~~~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/drivers/pwm.h:328:34: note: in expansion of macro 'PWM_DT_SPEC_GET_BY_IDX'
328 | #define PWM_DT_SPEC_GET(node_id) PWM_DT_SPEC_GET_BY_IDX(node_id, 0)
      |                                  ^~~~~~~~~~~~~~~~~~~~~~
C:/Clients/Venture/Phone/src/Keyboard/peripheral_hids_keyboard/src/speaker.c:16:32: note: in expansion of macro 'PWM_DT_SPEC_GET'
   16 | const struct pwm_dt_spec pwm = PWM_DT_SPEC_GET(DT_NODELABEL(pwm0));
      |                                ^~~~~~~~~~~~~~~
In file included from C:/ncs/v2.7.0/zephyr/include/zephyr/arch/arm/arch.h:20,
                 from C:/ncs/v2.7.0/zephyr/include/zephyr/arch/cpu.h:19,
                 from C:/ncs/v2.7.0/zephyr/include/zephyr/kernel_includes.h:36:
C:/Clients/Venture/Phone/src/Keyboard/peripheral_hids_keyboard/build/zephyr/include/generated/devicetree_generated.h:5965:36: error: 'DT_N_S_soc_S_pwm_4001c000_P_pwms_IDX_0_VAL_channel' undeclared here (not in a function); did you mean 'DT_N_S_soc_S_pwm_4001c000_REG_IDX_0_VAL_SIZE'?
5965 | #define DT_N_NODELABEL_pwm0        DT_N_S_soc_S_pwm_4001c000
      |                                    ^~~~~~~~~~~~~~~~~~~~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/devicetree.h:4543:9: note: in definition of macro 'DT_CAT7'
4543 |         a1 ## a2 ## a3 ## a4 ## a5 ## a6 ## a7
      |         ^~
C:/ncs/v2.7.0/zephyr/include/zephyr/devicetree/pwms.h:136:9: note: in expansion of macro 'DT_PHA_BY_IDX'
136 |         DT_PHA_BY_IDX(node_id, pwms, idx, cell)
      |         ^~~~~~~~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/devicetree/pwms.h:208:9: note: in expansion of macro 'DT_PWMS_CELL_BY_IDX'
208 |         DT_PWMS_CELL_BY_IDX(node_id, idx, channel)
      |         ^~~~~~~~~~~~~~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/drivers/pwm.h:261:28: note: in expansion of macro 'DT_PWMS_CHANNEL_BY_IDX'
261 |                 .channel = DT_PWMS_CHANNEL_BY_IDX(node_id, idx),               \
      |                            ^~~~~~~~~~~~~~~~~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/drivers/pwm.h:328:34: note: in expansion of macro 'PWM_DT_SPEC_GET_BY_IDX'
328 | #define PWM_DT_SPEC_GET(node_id) PWM_DT_SPEC_GET_BY_IDX(node_id, 0)
      |                                  ^~~~~~~~~~~~~~~~~~~~~~
C:/Clients/Venture/Phone/src/Keyboard/peripheral_hids_keyboard/src/speaker.c:16:32: note: in expansion of macro 'PWM_DT_SPEC_GET'
   16 | const struct pwm_dt_spec pwm = PWM_DT_SPEC_GET(DT_NODELABEL(pwm0));
      |                                ^~~~~~~~~~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/devicetree.h:4532:24: note: in expansion of macro 'DT_N_NODELABEL_pwm0'
4532 | #define DT_CAT(a1, a2) a1 ## a2
      |                        ^~
C:/ncs/v2.7.0/zephyr/include/zephyr/devicetree.h:200:29: note: in expansion of macro 'DT_CAT'
200 | #define DT_NODELABEL(label) DT_CAT(DT_N_NODELABEL_, label)
      |                             ^~~~~~
C:/Clients/Venture/Phone/src/Keyboard/peripheral_hids_keyboard/src/speaker.c:16:48: note: in expansion of macro 'DT_NODELABEL'
   16 | const struct pwm_dt_spec pwm = PWM_DT_SPEC_GET(DT_NODELABEL(pwm0));
      |                                                ^~~~~~~~~~~~
C:/Clients/Venture/Phone/src/Keyboard/peripheral_hids_keyboard/build/zephyr/include/generated/devicetree_generated.h:5965:36: error: 'DT_N_S_soc_S_pwm_4001c000_P_pwms_IDX_0_VAL_period' undeclared here (not in a function); did you mean 'DT_N_S_soc_S_pwm_4001c000_IRQ_IDX_0_VAL_irq'?
5965 | #define DT_N_NODELABEL_pwm0        DT_N_S_soc_S_pwm_4001c000
      |                                    ^~~~~~~~~~~~~~~~~~~~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/devicetree.h:4543:9: note: in definition of macro 'DT_CAT7'
4543 |         a1 ## a2 ## a3 ## a4 ## a5 ## a6 ## a7
      |         ^~
C:/ncs/v2.7.0/zephyr/include/zephyr/devicetree/pwms.h:136:9: note: in expansion of macro 'DT_PHA_BY_IDX'
136 |         DT_PHA_BY_IDX(node_id, pwms, idx, cell)
      |         ^~~~~~~~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/devicetree/pwms.h:249:9: note: in expansion of macro 'DT_PWMS_CELL_BY_IDX'
249 |         DT_PWMS_CELL_BY_IDX(node_id, idx, period)
      |         ^~~~~~~~~~~~~~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/drivers/pwm.h:262:27: note: in expansion of macro 'DT_PWMS_PERIOD_BY_IDX'
262 |                 .period = DT_PWMS_PERIOD_BY_IDX(node_id, idx),                 \
      |                           ^~~~~~~~~~~~~~~~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/drivers/pwm.h:328:34: note: in expansion of macro 'PWM_DT_SPEC_GET_BY_IDX'
328 | #define PWM_DT_SPEC_GET(node_id) PWM_DT_SPEC_GET_BY_IDX(node_id, 0)
      |                                  ^~~~~~~~~~~~~~~~~~~~~~
C:/Clients/Venture/Phone/src/Keyboard/peripheral_hids_keyboard/src/speaker.c:16:32: note: in expansion of macro 'PWM_DT_SPEC_GET'
   16 | const struct pwm_dt_spec pwm = PWM_DT_SPEC_GET(DT_NODELABEL(pwm0));
      |                                ^~~~~~~~~~~~~~~
C:/ncs/v2.7.0/zephyr/include/zephyr/devicetree.h:4532:24: note: in expansion of macro 'DT_N_NODELABEL_pwm0'
4532 | #define DT_CAT(a1, a2) a1 ## a2
      |                        ^~
C:/ncs/v2.7.0/zephyr/include/zephyr/devicetree.h:200:29: note: in expansion of macro 'DT_CAT'
200 | #define DT_NODELABEL(label) DT_CAT(DT_N_NODELABEL_, label)
      |                             ^~~~~~
C:/Clients/Venture/Phone/src/Keyboard/peripheral_hids_keyboard/src/speaker.c:16:48: note: in expansion of macro 'DT_NODELABEL'
   16 | const struct pwm_dt_spec pwm = PWM_DT_SPEC_GET(DT_NODELABEL(pwm0));
      |                                                ^~~~~~~~~~~~

RE: How to configure 2 PWM pins with same frequency and duty cycle but opposite polarity

mkjones — Thu, 14 Nov 2024 18:02:37 GMT

Since my duty cycle is 50%, the pulse length for pwm_2 is exactly the same as pmw_1; I don't understand how this gets the opposite polarity.

Maybe there's something I need to do in the overlay file where I define the PWMs?

RE: How to configure 2 PWM pins with same frequency and duty cycle but opposite polarity

Susheel Nuguru — Wed, 13 Nov 2024 07:41:49 GMT

Try this code for inverted PWM after you configured two PWM in the device tree

const struct pwm_dt_spec pwm_1 = PWM_DT_SPEC_GET(DT_ALIAS(pwm0));
const struct pwm_dt_spec pwm_2 = PWM_DT_SPEC_GET(DT_ALIAS(pwm1));

void configure_pwm_opposite_polarity(uint32_t period_usec, uint32_t duty_cycle_usec)
{
    if (!device_is_ready(pwm_1.dev) || !device_is_ready(pwm_2.dev)) {
        printk("Error: PWM device is not ready.\n");
        return;
    }

    // Set PWM for the first channel (normal polarity)
    pwm_set_dt(&pwm_1, period_usec, duty_cycle_usec);

    // Set PWM for the second channel (inverted polarity)
    pwm_set_dt(&pwm_2, period_usec, period_usec - duty_cycle_usec);
}