RE: nRF52840 How to play 2 PWM sequences in one channel with different duty cycle in Common Mode?

Sigurd — Tue, 07 Sep 2021 11:30:21 GMT

Hi,

[quote user=""]For example, the 1st pulse at 100% 1000ms ON / 1000ms OFF and the 2nd pattern sequence at 25% duty cycle with the same 1000ms / 1000ms OFF.[/quote]

Here is some example code for that, based on pwm_driver example in nRF5SDK.

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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_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

static nrf_drv_pwm_t m_pwm0 = NRF_DRV_PWM_INSTANCE(0);

#define PWM_PIN 3
#define TOP_VALUE 1000

#define LOW 0x8000
#define HIGH 0

static void pwm_init(void)
{
    nrf_drv_pwm_config_t config =
    {
        // These are the common configuration options we use for all PWM
        // instances.
        .irq_priority = APP_IRQ_PRIORITY_LOWEST,
        .count_mode   = NRF_PWM_MODE_UP,
        .step_mode    = NRF_PWM_STEP_AUTO,
    };

    config.base_clock = NRF_PWM_CLK_1MHz;
    config.top_value  = TOP_VALUE;
    config.load_mode  = NRF_PWM_LOAD_COMMON;

    config.output_pins[0] = PWM_PIN;
    config.output_pins[1] = NRF_DRV_PWM_PIN_NOT_USED;
    config.output_pins[2] = NRF_DRV_PWM_PIN_NOT_USED;
    config.output_pins[3] = NRF_DRV_PWM_PIN_NOT_USED;
    APP_ERROR_CHECK(nrf_drv_pwm_init(&m_pwm0, &config, NULL));
}

static void start_pwm_demo()
{
    // Sequence 0:   1000ms high level, 1000ms low level
    static nrf_pwm_values_common_t seq0_values[] =
    {
       HIGH , LOW
    };

    nrf_pwm_sequence_t const pwm0_seq0 =
    {
        .values.p_common = seq0_values,    
        .length          = NRF_PWM_VALUES_LENGTH(seq0_values),
        .repeats         = 1000,
        .end_delay       = 0
    };



    // Sequence 1 : 25% duty cycle for 1000ms high, then low for 1000ms.
   static nrf_pwm_values_common_t seq1_values[] =
   {
    TOP_VALUE-(TOP_VALUE/4) | HIGH, LOW
   };

    nrf_pwm_sequence_t const pwm0_seq1 =
    {
        .values.p_common = seq1_values,
        .length          = NRF_PWM_VALUES_LENGTH(seq1_values),
        .repeats         = 1000,
        .end_delay       = 1000-1
    };

    (void)nrf_drv_pwm_complex_playback(&m_pwm0, &pwm0_seq0, &pwm0_seq1, 1,
                                       NRF_DRV_PWM_FLAG_LOOP);


}



static void bsp_evt_handler(bsp_event_t evt)
{

    switch (evt)
    {
        // Button 1 on DK - start pwm demo
        case BSP_EVENT_KEY_0:
             //start_pwm_demo();
             break;
            
        default:
            return;
    }

}



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);
}

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

    APP_ERROR_CHECK(app_timer_init());
    APP_ERROR_CHECK(bsp_init(BSP_INIT_BUTTONS, bsp_evt_handler));
    APP_ERROR_CHECK(bsp_buttons_enable());
}


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


    NRF_LOG_INFO("PWM example started.");
    init_bsp();

    bool accurate_HFCLK = true;

    if(accurate_HFCLK)
    {
      // Start accurate HFCLK (XOSC) (will consume more current)
      NRF_CLOCK->TASKS_HFCLKSTART = 1;
      while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0) ;
      NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
    }

    pwm_init();

    start_pwm_demo();

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

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

        NRF_LOG_FLUSH();
    }
}


/** @} */

Output:

RE: nRF52840 How to play 2 PWM sequences in one channel with different duty cycle in Common Mode?

fabocode — Mon, 06 Sep 2021 13:59:30 GMT

Hi,

Thanks for your reply.

Here's the configuration for the PWM instance. From what I can understand

.base_clock = (nrf_pwm_clk_t)NRFX_PWM_DEFAULT_CONFIG_BASE_CLOCK

which in the sdk_config.h is set to 1MHz and the .top_value =

NRFX_PWM_DEFAULT_CONFIG_TOP_VALUE is equal to 1000.

nrfx_pwm_handler_t pwm_handler = NULL;
const nrfx_pwm_config_t pwm_motor_cfg = {
.output_pins  = { p_config->gpio_motor,
                      NRFX_PWM_PIN_NOT_USED,
                      NRFX_PWM_PIN_NOT_USED,
                      NRFX_PWM_PIN_NOT_USED,},
    .irq_priority = NRFX_PWM_DEFAULT_CONFIG_IRQ_PRIORITY,
    .base_clock   = (nrf_pwm_clk_t)NRFX_PWM_DEFAULT_CONFIG_BASE_CLOCK,
    .count_mode   = (nrf_pwm_mode_t)NRFX_PWM_DEFAULT_CONFIG_COUNT_MODE,
    .top_value    = NRFX_PWM_DEFAULT_CONFIG_TOP_VALUE,
    .load_mode    = (nrf_pwm_dec_load_t)NRF_PWM_LOAD_COMMON,
    .step_mode    = (nrf_pwm_dec_step_t)NRFX_PWM_DEFAULT_CONFIG_STEP_MODE,
};

// initialize the pwm module 
nrfx_pwm_init(p_instance->p_drv_instance, &pwm_motor_cfg, pwm_handler);

I also want to understand how the values represent when is in the pwm_sequence.values.p_raw.

I checked in the API that p_raw is a pointer providing raw access to the values, but I would like to understand how can I set values to it without knowing what exactly means each bit.

RE: nRF52840 How to play 2 PWM sequences in one channel with different duty cycle in Common Mode?

Sigurd — Mon, 06 Sep 2021 12:28:26 GMT

Hi,

[quote userid="84523" url="~/f/nordic-q-a/79309/nrf52840-how-to-play-2-pwm-sequences-in-one-channel-with-different-duty-cycle-in-common-mode"]For example, the 1st pulse at 100% 1000ms ON / 1000ms OFF and the 2nd pattern sequence at 25% duty cycle with the same 1000ms / 1000ms OFF.[/quote]

I can create small example that does this. What frequency should this 2nd pattern use?