nrf52840 PWM Driver update duty cycle

RE: nrf52840 PWM Driver update duty cycle

Håkon — Tue, 05 Nov 2019 10:09:52 GMT

Hi,

This method for changing duty cycle values is OK, it's simple and clear.
This post uses this method as well to implement a neat RGB pwm dimmer using only one PMW instance.
It could be nice to take a look there.

RE: nrf52840 PWM Driver update duty cycle

BEplane — Mon, 04 Nov 2019 16:08:18 GMT

I was able to solve the the dimming problem with changing the math operation around.

Do you have any input on this method vs nrfx_pwm_sequence_values_update?

RE: nrf52840 PWM Driver update duty cycle

Håkon — Mon, 04 Nov 2019 15:41:48 GMT

Hi,

I printed the duty cycle from the update_pwm function. It seems the equation output returned 0 a lot of times.
This is because dividing two integers where duty_cycle is between 0 and 100, with 100 will result in 0 (when duty_cycle is less than 100).
Either use float/double or do as my example where I devide PWM_TOP with 100 first, then multiply with duty_cycle.

Could you try me code example attached and see if this suit your needs?

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/** @file
 * @defgroup pwm_example_main main.c
 * @{
 * @ingroup pwm_example
 *
 * @brief PWM Example Application main file.
 *
 * This file contains the source code for a sample application using PWM.
 */

#include <stdio.h>
#include <string.h>
#include "nrf_drv_pwm.h"
#include "app_util_platform.h"
#include "app_error.h"
#include "boards.h"
#include "bsp.h"
#include "app_timer.h"
#include "nrf_drv_clock.h"

#include "nrf_delay.h"
#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

#define PWM_TOP_VALUE 1000

static nrf_drv_pwm_t m_pwm0 = NRF_DRV_PWM_INSTANCE(0);

static nrf_pwm_values_individual_t m_LED_seq_values;
static nrf_pwm_sequence_t const m_LED_seq =
{
    .values.p_individual = &m_LED_seq_values,
    .length          = NRF_PWM_VALUES_LENGTH(m_LED_seq_values),
    .repeats         = 0,
    .end_delay       = 0
};

static void update_LED(uint8_t duty_cycle)
{
    uint16_t pwm_count = PWM_TOP_VALUE/100;
    if(duty_cycle <= 100)
        {
            pwm_count = pwm_count * duty_cycle;
        }
    else
    {
        NRF_LOG_ERROR("Duty cycle input not valid");
    }
    
    //nrf_pwm_values_common_t const *p_pwm_count = pwm_count;
    //nrfx_pwm_sequence_values_update(&m_pwm0,0, p_pwm_count);
    NRF_LOG_INFO("pwm_count: %d", pwm_count);
    m_LED_seq_values.channel_0 = pwm_count;
    //nrf_drv_pwm_simple_playback(&m_pwm0, &m_LED_seq, 1, NRF_DRV_PWM_FLAG_LOOP);
}


static void single_LED_dimmer_init(void)
{
    NRF_LOG_INFO("LED dimmer init");

    nrf_drv_pwm_config_t const config0 =
    {
        .output_pins =
        {
            BSP_LED_0 | NRF_DRV_PWM_PIN_INVERTED, // channel 0
            NRF_DRV_PWM_PIN_NOT_USED,             // channel 1
            NRF_DRV_PWM_PIN_NOT_USED,             // channel 2
            NRF_DRV_PWM_PIN_NOT_USED,             // channel 3
        },
        .irq_priority = APP_IRQ_PRIORITY_LOWEST,  //< Interrupt priority.
        .base_clock   = NRF_PWM_CLK_2MHz,         //< Base clock frequency.
        .count_mode   = NRF_PWM_MODE_UP,          //< Operating mode of the pulse generator counter.
        .top_value    = PWM_TOP_VALUE,            //< Value up to which the pulse generator counter counts.
        .load_mode    = NRF_PWM_LOAD_INDIVIDUAL,  //< Mode of loading sequence data from RAM.
        .step_mode    = NRF_PWM_STEP_AUTO         //< Mode of advancing the active sequence.
    };
    
    m_LED_seq_values.channel_0 = PWM_TOP_VALUE; // Initially set to 100 %
    APP_ERROR_CHECK(nrf_drv_pwm_init(&m_pwm0, &config0, NULL));
    nrf_drv_pwm_simple_playback(&m_pwm0, &m_LED_seq, 1, NRF_DRV_PWM_FLAG_LOOP);
}


int main(void)
{
    APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
    NRF_LOG_DEFAULT_BACKENDS_INIT();


    NRF_LOG_INFO("PWM example started.");

    // Start with Demo 1, then switch to another one when the user presses
    // button 1 or button 2 (see the 'bsp_evt_handler' function).

    single_LED_dimmer_init();
    nrf_delay_ms(2000);
    update_LED(10);
    nrf_delay_ms(2000);
    update_LED(50);
    nrf_delay_ms(2000);
    update_LED(100);
    nrf_delay_ms(2000);
    update_LED(0);


    for (;;)
    {
        // Wait for an event.
        __WFE();

        // Clear the event register.
        __SEV();
        __WFE();

        NRF_LOG_FLUSH();
    }
}


/** @} */

Best regards,
Håkon

RE: nrf52840 PWM Driver update duty cycle

BEplane — Mon, 04 Nov 2019 14:27:27 GMT

I am able to build and run the one of the methods, although the LED is not being dimmed. I have tested previously that sequence value = 16k is ~50% duty cycle and the LED is dimmed as expected, but this was by changing the value and recompiling. What I am seeing with this code is the LED is 100%, but for a duty cycle of 50% the LED is turned off.

SDK: 15.3.0

Hardware: nRF52840-DK

#include <stdio.h>
#include <string.h>
#include "nrf_drv_pwm.h"
#include "app_util_platform.h"
#include "app_error.h"
#include "boards.h"
#include "bsp.h"
#include "app_timer.h"
#include "nrf_drv_clock.h"

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

#include "nrf_delay.h"

static nrf_drv_pwm_t m_pwm0 = NRF_DRV_PWM_INSTANCE(0);


static uint8_t m_used = 0;


nrf_pwm_values_individual_t seq_values_test[] = { 16384};
nrf_pwm_sequence_t const seq_test =
{
    .values.p_individual = seq_values_test,
    .length          = NRF_PWM_VALUES_LENGTH(seq_values_test),
    .repeats         = 0,
    .end_delay       = 0
};


static void update_LED(uint16_t duty_cycle)
{
    uint16_t pwm_count = 32768 *(duty_cycle / 100);
    //nrf_pwm_values_common_t const *p_pwm_count = pwm_count;
    //nrfx_pwm_sequence_values_update(&m_pwm0,0, p_pwm_count);
    
    seq_values_test->channel_0 = pwm_count;
    nrf_drv_pwm_simple_playback(&m_pwm0, &seq_test, 1, NRF_DRV_PWM_FLAG_LOOP);
}

static void demo3(void)
{
    NRF_LOG_INFO("Demo 3");

    nrf_drv_pwm_config_t const config0 =
    {
        .output_pins =
        {
            BSP_LED_0 | NRF_DRV_PWM_PIN_INVERTED, // channel 0
            NRF_DRV_PWM_PIN_NOT_USED,             // channel 1
            NRF_DRV_PWM_PIN_NOT_USED,             // channel 2
            NRF_DRV_PWM_PIN_NOT_USED,             // channel 3
        },
        .irq_priority = APP_IRQ_PRIORITY_LOWEST,
        .base_clock   = NRF_PWM_CLK_2MHz, //NRF_PWM_CLK_125kHz,
        .count_mode   = NRF_PWM_MODE_UP,
        .top_value    = 32768, //25000,
        .load_mode    = NRF_PWM_LOAD_INDIVIDUAL,
        .step_mode    = NRF_PWM_STEP_AUTO
    };
    APP_ERROR_CHECK(nrf_drv_pwm_init(&m_pwm0, &config0, NULL));
}

static void init_bsp()
{
    APP_ERROR_CHECK(nrf_drv_clock_init());
    nrf_drv_clock_lfclk_request(NULL);

    APP_ERROR_CHECK(app_timer_init());

}


void app_error_fault_handler(uint32_t id, uint32_t pc, uint32_t info)
{
    bsp_board_leds_on();
    app_error_save_and_stop(id, pc, info);
}


int main(void)
{
    APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
    NRF_LOG_DEFAULT_BACKENDS_INIT();

    init_bsp();

    NRF_LOG_INFO("PWM example started.");

    // Start with Demo 1, then switch to another one when the user presses
    // button 1 or button 2 (see the 'bsp_evt_handler' function).
    demo3();
    nrf_delay_ms(2000);
    update_LED(100);
    nrf_delay_ms(2000);
    update_LED(50);
    nrf_delay_ms(2000);
    update_LED(100);
    nrf_delay_ms(2000);
    update_LED(50);
    NRF_LOG_FLUSH();


    for (;;)
    {
        // Wait for an event.
        __WFE();

        // Clear the event register.
        __SEV();
        __WFE();

        NRF_LOG_FLUSH();
    }
    
}