PWM output specific waveform

[Jim]

I am using nrf52832 sdk14.2.0 to develop now, I want to realize the following function on the basis of PWM_driver example, output the following waveform on P0.22: 1ms high level, 100ms low level, 2ms high level, need to realize how? If you use 1ms as the base, then you need to write more than 100 data in pwm0_seq_values. Is there any good way?

[Sigurd]

Hi Jim,

Here is an example on how to implement this with the PWM driver. Instead of "writing more than 100 data in pwm0_seq_values" you can use the end_delay functionality. You can copy-paste this into the PWM driver example in the SDK to test it. When you press button 1 on the DK, the PWM waveform is started.

/**
 * Copyright (c) 2015 - 2018, Nordic Semiconductor ASA
 * 
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 * 
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 * 
 * 2. Redistributions in binary form, except as embedded into a Nordic
 *    Semiconductor ASA integrated circuit in a product or a software update for
 *    such product, must reproduce the above copyright notice, this list of
 *    conditions and the following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 * 
 * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 * 
 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
 * 
 * 5. Any software provided in binary form under this license must not be reverse
 *    engineered, decompiled, modified and/or disassembled.
 * 
 * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY, NONINFRINGEMENT, AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL NORDIC SEMICONDUCTOR ASA OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 * 
 */
/** @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 22

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  = 1000;
    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:   1ms high level, 100ms low level
    static nrf_pwm_values_common_t seq0_values[] =
    {
       0x8000, 0,0x8000
    };

    nrf_pwm_sequence_t const pwm0_seq0 =
    {
        .values.p_common = seq0_values,    
        .length          = NRF_PWM_VALUES_LENGTH(seq0_values),
        .repeats         = 0,
        .end_delay       = 100
    };



    // Sequence 1 : 2ms high, then low.
   static nrf_pwm_values_common_t seq1_values[2] = {0,0};

    nrf_pwm_sequence_t const pwm0_seq1 =
    {
        .values.p_common = seq1_values,
        .length          = NRF_PWM_VALUES_LENGTH(seq1_values),
        .repeats         = 0,
        .end_delay       = 0
    };

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


}



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)
      NRF_CLOCK->TASKS_HFCLKSTART = 1;
      while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0) ;
      NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
    }

    pwm_init();

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

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

        NRF_LOG_FLUSH();
    }
}


/** @} */