Please give me advice on nrf pwm driver.

Question

I want a waveform as below for motor control. I am trying to create this using nrf pwm driver. 
 I set the pwm sequence as below and checked the output. 2nd duty repeat does not work. 
 I added an unused 3rd dummy duty (line 91). It seems to be working well. 
 However, increasing the playback count to 2 introduces a delay between the outputs. 
 What should I do to get the waveform I want? Give me advice . Thanks.

Jared · Accepted Answer

Hi there,

Although it's not well explained in the product specification, the PWM peripheral has a limitation in that it will stop the execution of a sequence too early. Some effort has been done to explain it in some part in this thread.

Nevertheless, the best way for your use case is to something like this:

#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"

static nrf_drv_pwm_t m_pwm0 = NRF_DRV_PWM_INSTANCE(0);

#define PERIOD 1000

#define DUTY		75
#define HIGH		(PERIOD * (100 - DUTY) / 100) //250
#define LOW			PERIOD //1000 

static nrf_pwm_values_individual_t /*const*/ seq_values[] =
{
    
	{HIGH, LOW, LOW, LOW},
	{HIGH, LOW, LOW, LOW},
    {HIGH, LOW, LOW, LOW},
    {HIGH, LOW, LOW, LOW},
    {LOW, HIGH, LOW, LOW},
    {LOW, HIGH, LOW, LOW},
    {LOW, HIGH, LOW, LOW},
    {LOW, HIGH, LOW, LOW},
};
nrf_pwm_sequence_t const seq =
{
	.values.p_individual = seq_values,
	.length              = NRF_PWM_VALUES_LENGTH(seq_values),
	.repeats             = 0
	,
	.end_delay           = 0
};

static void demo(void)
{
    nrf_drv_pwm_config_t const config0 =
    {
        .output_pins =
        {
            3,
            4,
            NRFX_PWM_PIN_NOT_USED,
            NRFX_PWM_PIN_NOT_USED
        },
        .irq_priority = APP_IRQ_PRIORITY_LOWEST,
        .base_clock   = NRF_PWM_CLK_1MHz,
        .count_mode   = NRF_PWM_MODE_UP,
		.top_value    = 1000,
        .load_mode    = PWM_DECODER_LOAD_Individual,
        .step_mode    = NRF_PWM_STEP_AUTO
    };
    APP_ERROR_CHECK(nrf_drv_pwm_init(&m_pwm0, &config0, NULL));
}


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

int main(void)
{

	demo();
	
    for (;;)
    {
		(void)nrf_drv_pwm_simple_playback(&m_pwm0, &seq, 4 , NRFX_PWM_FLAG_STOP);

		nrf_delay_ms(1000);
    }
}

Note, I changed the pins so you should probably change them back ;)

Instead of using the repeat, I hardcoded the sequence pattern and use the playback_count parameter to nrfx_pwm_simple_playback() to decide the number of times the pattern should be repeated. Here is a trace from the logic analyzer with playback_count set to 4:

best regards

Jared

John Lee · Answer

I solved it. Thank you for the answer.

Please give me advice on nrf pwm driver.

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