Stop and start PWM with a PPI

[Ros]

Hi,

Is there anyway to start after stopping the PWM with a PPI channel?

There is a start task in the PWM, but

But not defined in the nrfx pwm driver (nrf_pwm.h)

/** @brief PWM tasks. */
typedef enum
{
    NRF_PWM_TASK_STOP      = offsetof(NRF_PWM_Type, TASKS_STOP),             ///< Stops PWM pulse generation on all channels at the end of the current PWM period, and stops the sequence playback.
#if NRF_PWM_HAS_DMA_TASKS_EVENTS
    NRF_PWM_TASK_SEQSTART0 = offsetof(NRF_PWM_Type, TASKS_DMA.SEQ[0].START), ///< Starts playback of sequence 0.
    NRF_PWM_TASK_SEQSTART1 = offsetof(NRF_PWM_Type, TASKS_DMA.SEQ[1].START), ///< Starts playback of sequence 1.
#else
    NRF_PWM_TASK_SEQSTART0 = offsetof(NRF_PWM_Type, TASKS_SEQSTART[0]),      ///< Starts playback of sequence 0.
    NRF_PWM_TASK_SEQSTART1 = offsetof(NRF_PWM_Type, TASKS_SEQSTART[1]),      ///< Starts playback of sequence 1.
#endif
    NRF_PWM_TASK_NEXTSTEP  = offsetof(NRF_PWM_Type, TASKS_NEXTSTEP)          ///< Steps by one value in the current sequence if the decoder is set to @ref NRF_PWM_STEP_TRIGGERED mode.
} nrf_pwm_task_t;

I'm developing a battery application, and the PWM is only needed for a short time, in regular intervals.

[Sigurd]

Hi!,

Yes, use NRF_PWM_TASK_SEQSTART0

#include <hal/nrf_pwm.h>

[Ros]

Sigurd said:

Yes, use NRF_PWM_TASK_SEQSTART0

No, it cannot start after stopping the PWM (it triggers only once after initialization).

[Sigurd]

Something is then maybe wrong with your PPI configuration. 

this simple "bare-metal" test shows that it can re-start using that task.

#include <nrf.h>

#include <hal/nrf_pwm.h>

#include <zephyr/kernel.h>


#define PWM_PIN (13UL)


int16_t buf[] = {(1 << 15) | 10000}; // Inverse polarity (bit 15)

int main(void)
{
  // Start accurate HFCLK (XOSC)
  NRF_CLOCK->TASKS_HFCLKSTART = 1;
  while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0) ;
  NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
  
  // Configure PWM_PIN as output, and set it to 0
  NRF_GPIO->DIRSET = (1 << PWM_PIN);
  NRF_GPIO->OUTCLR = (1 << PWM_PIN);
  
  
  NRF_PWM0->PRESCALER   = PWM_PRESCALER_PRESCALER_DIV_16; // 1 us
  NRF_PWM0->PSEL.OUT[0] = PWM_PIN;
  NRF_PWM0->MODE        = (PWM_MODE_UPDOWN_Up << PWM_MODE_UPDOWN_Pos);
  NRF_PWM0->DECODER     = (PWM_DECODER_LOAD_Common       << PWM_DECODER_LOAD_Pos) | 
                          (PWM_DECODER_MODE_RefreshCount << PWM_DECODER_MODE_Pos);
  NRF_PWM0->LOOP        = (PWM_LOOP_CNT_Disabled << PWM_LOOP_CNT_Pos);
  
  NRF_PWM0->COUNTERTOP = 20000; // 20ms period
  
  
  NRF_PWM0->SEQ[0].CNT = ((sizeof(buf) / sizeof(uint16_t)) << PWM_SEQ_CNT_CNT_Pos);
  NRF_PWM0->SEQ[0].ENDDELAY = 0;
  NRF_PWM0->SEQ[0].PTR = (uint32_t)&buf[0];
  NRF_PWM0->SEQ[0].REFRESH = 0;
  NRF_PWM0->SHORTS = 0;
  
  NRF_PWM0->ENABLE = 1;
  NRF_PWM0->TASKS_SEQSTART[0] = 1;

  k_msleep(1000);
  nrf_pwm_task_trigger(NRF_PWM0,NRF_PWM_TASK_STOP);
  k_msleep(1000);
  nrf_pwm_task_trigger(NRF_PWM0,NRF_PWM_TASK_SEQSTART0);


  k_msleep(1000);
  nrf_pwm_task_trigger(NRF_PWM0,NRF_PWM_TASK_STOP);
  k_msleep(1000);
  nrf_pwm_task_trigger(NRF_PWM0,NRF_PWM_TASK_SEQSTART0);


}

[Ros]

I have used the PPI to trigger GPIOTE and it works fine, but don't know why it not works with PWM, the code is below:

[Ros]

I have used the PPI to trigger GPIOTE and it works fine, but don't know why it not works with PWM, the code is below:

#include <nrfx_saadc.h>

#include <nrfx_timer.h>

#include <nrfx_ppi.h>

#include <nrfx_pwm.h>

#include <nrfx_rtc.h>

#include <nrfx_gpiote.h>

#include <zephyr/kernel.h>

#include <zephyr/logging/log.h>

#define LED0    DT_GPIO_PIN(DT_ALIAS(led0), gpios)

#define LED1    DT_GPIO_PIN(DT_ALIAS(led1), gpios)

// #define LED0    14

// #define LED1   15

#define RTC_INSTANCE    2

// #define SAMPLE_INTERVAL_MS      250

#define SAMPLE_INTERVAL_MS      4000

static nrfx_pwm_t pwm_instance = NRFX_PWM_INSTANCE(0);

LOG_MODULE_REGISTER(pwm_gen, LOG_LEVEL_DBG);

const nrfx_rtc_t rtc = NRFX_RTC_INSTANCE(RTC_INSTANCE);

void pwm_event_handler(nrfx_pwm_evt_type_t event_type, void *p_context)

{

    switch (event_type) {

        case NRFX_PWM_EVT_FINISHED:

            //nrfx_pwm_stop(&pwm_instance, false);

            LOG_DBG("PWM finished");

            break;

        case NRFX_PWM_EVT_END_SEQ0:

            LOG_DBG("PWM end sequence 0");

            break;

        case NRFX_PWM_EVT_END_SEQ1:

            LOG_DBG("PWM end sequence 1");

            break;

        case NRFX_PWM_EVT_STOPPED:

            LOG_DBG("PWM stopped");

            break;

        default:

            LOG_ERR("PWM event: %d", event_type);

            break;

    }

}

void rtc_event_handler(nrfx_rtc_int_type_t int_type)

{

    static int32_t cnt = 0;

    LOG_DBG("RTC Interrupt: %d, %d", int_type, cnt++);

}

#define NRFX_RTC_IRQ_HANDLER(instance) CONCAT(nrfx_rtc_, instance, _irq_handler)

#define NRFX_RTC_MS_TO_TICKS(us,freq) (((us) * (freq)) / 1000U)

#define GPIOTE_INST NRF_DT_GPIOTE_INST(DT_ALIAS(led3), gpios)

#define OUTPUT_PIN NRF_DT_GPIOS_TO_PSEL(DT_ALIAS(led3), gpios)

void init_pwm()

{

    static nrfx_pwm_config_t pwm_config = NRFX_PWM_DEFAULT_CONFIG(LED0, LED1,

        NRF_PWM_PIN_NOT_CONNECTED, NRF_PWM_PIN_NOT_CONNECTED);

    IRQ_CONNECT(DT_IRQN(DT_NODELABEL(pwm0)),

                DT_IRQ(DT_NODELABEL(pwm0), priority),

                nrfx_isr, nrfx_pwm_0_irq_handler, 0);

    pwm_config.base_clock = NRF_PWM_CLK_125kHz;

    pwm_config.count_mode = NRF_PWM_MODE_UP_AND_DOWN;

    pwm_config.load_mode = NRF_PWM_LOAD_INDIVIDUAL;

    pwm_config.step_mode = NRF_PWM_STEP_TRIGGERED;

    pwm_config.top_value = 65535;    

    pwm_config.pin_inverted[0] = true;

    pwm_config.pin_inverted[1] = true;

    if (nrfx_pwm_init(&pwm_instance, &pwm_config, &pwm_event_handler, &pwm_instance) != NRFX_SUCCESS) {

        LOG_ERR("Failed to initialize PWM");

        return;

    }

    static nrf_pwm_values_individual_t seq_values = {

        .channel_0 = 16383,

        .channel_1 = 4095,

        .channel_2 = 0,

        .channel_3 = 0

    };

    static nrf_pwm_sequence_t seq = {

        .values.p_individual = &seq_values,

        .length = NRF_PWM_VALUES_LENGTH(seq_values),

        .repeats = 0,

        .end_delay = 0

    };

    static uint32_t pwm0_start_task;

    pwm0_start_task = nrfx_pwm_simple_playback(&pwm_instance, &seq, 1,  NRFX_PWM_FLAG_STOP);

    //pwm0_start_task = nrfx_pwm_simple_playback(&pwm_instance, &seq, 1, NRFX_PWM_FLAG_STOP);

    LOG_DBG("PWM initialized");

    nrfx_err_t err;

    nrfx_rtc_config_t rtc_cfg = NRFX_RTC_DEFAULT_CONFIG;

    IRQ_CONNECT(DT_IRQN(DT_NODELABEL(CONCAT(rtc, RTC_INSTANCE))),

                DT_IRQ(DT_NODELABEL(CONCAT(rtc, RTC_INSTANCE)), priority),

                nrfx_isr, NRFX_RTC_IRQ_HANDLER(RTC_INSTANCE), 0);

    err = nrfx_rtc_init(&rtc, &rtc_cfg, rtc_event_handler);

    if (err != NRFX_SUCCESS) {

        LOG_ERR("Failed to initialize RTC-0, %d", err);

        return;

    }

    uint32_t rtc_ticks = NRFX_RTC_MS_TO_TICKS(SAMPLE_INTERVAL_MS, NRF_RTC_INPUT_FREQ);

    err = nrfx_rtc_cc_set(&rtc, 0, rtc_ticks, false);

    if (err != NRFX_SUCCESS) {

        LOG_ERR("Failed to set RTC comparator");

    }

    nrf_ppi_channel_t m_rtc_counter_clear;

    nrfx_ppi_channel_alloc(&m_rtc_counter_clear);

    /* channel, eep, tep task endpoint address*/

    nrfx_ppi_channel_assign(m_rtc_counter_clear,

        nrfx_rtc_event_address_get(&rtc, NRF_RTC_EVENT_COMPARE_0),

            nrfx_rtc_task_address_get(&rtc, NRF_RTC_TASK_CLEAR));

    nrfx_ppi_channel_fork_assign(m_rtc_counter_clear, nrfx_pwm_task_address_get(&pwm_instance, NRF_PWM_TASK_SEQSTART0));

    //nrfx_ppi_channel_fork_assign(m_rtc_counter_clear, nrfx_pwm_task_address_get(&pwm_instance, NRF_PWM_TASK_STOP));

    //nrfx_ppi_channel_fork_assign(m_rtc_counter_clear, pwm0_start_task);

    // Enable PPI before enabling RTC

    nrfx_ppi_channel_enable(m_rtc_counter_clear);

    nrfx_rtc_enable(&rtc);

}

[Sigurd]

Hi!
I will test your code.
Could you let me know what SDK version you are using?

[Ros]

I'm using nrfconnect v2.9.0