nRF52832 PWM sequence endlessly by easyDMA

RE: nRF52832 PWM sequence endlessly by easyDMA

Sigurd — Thu, 08 Jun 2017 13:02:31 GMT

The reason why I used SEQ[1].CNT = 7, and SEQ[1].REFRESH = 36 in order to make it 259 cycles, is that the REFRESH value is ignored when CNT =1 for SEQ[1]. So you cannot have SEQ[1].CNT =1 and SEQ[1].REFRESH = 258 for SEQ[1]. This is explained in the PWM Product Specification, quote:

SEQ[n].REFRESH and SEQ[n].ENDDELAY are ignored at the end of a complex sequence, indicated by a LOOPSDONE event. The reason for this is that the last value loaded from RAM is maintained until further action from software (restarting a new sequence, or stopping PWM generation).

So you need SEQ[1].CNT > 1. The solution with SEQ[1].CNT = 7, and SEQ[1].REFRESH = 36 is fully reasonable and appliable in order to get 269 cycles.

RE: nRF52832 PWM sequence endlessly by easyDMA

kojima — Thu, 08 Jun 2017 12:17:06 GMT

Dear sigurdon,

Thank you very much for showing me a good code sippet.

Have you considered using the PWM driver in the SDK? No. not yet. Because I did NOT learn enough about the basic philothopy of Nordic's SDK coding structure and style to write MY OWN code along that.

Here is some code that will give you 3 cycles of DUTY A, and 259 cycles of DUTY B, and will loop >forever. This is with EasyDMA, and with no CPU usage.

This is very similar to MY experimental code just done last night!. I fould LOAD_COMMON would be the reasonable choice. But, I'm not sure this is the reasonable and universally-appliable solution or not... Because, this code includes very puzzly magic number combination for Duty-B cycles. I'd also found that (7)*(36+1) can make up 259 and employing REFRESH.

How do you think ?

P.S. Regarding three cycles for Duty-A, I did employing REFRESH=(3-1), CNT=1 to save RAM space.

RE: nRF52832 PWM sequence endlessly by easyDMA

Sigurd — Thu, 08 Jun 2017 11:38:53 GMT

Hi,

Have you considered using the PWM driver in the SDK?

Here is some code that will give you 3 cycles of DUTY A, and 259 cycles of DUTY B, and will loop forever. This is with EasyDMA, and with no CPU usage.

Code snippet:

#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 "nrf_drv_clock.h"
#include "nrf_delay.h"


#define OUTPUT_PIN 4

#define DUTY_A 50
#define DUTY_B 80

static nrf_drv_pwm_t m_pwm0 = NRF_DRV_PWM_INSTANCE(0);


static nrf_pwm_values_common_t /*const*/ seq0_values[] =
{
         DUTY_A,DUTY_A,DUTY_A
};

nrf_pwm_sequence_t const seq0 =
{
    .values.p_common = seq0_values,
    .length          = NRF_PWM_VALUES_LENGTH(seq0_values),
    .repeats         = 0,
    .end_delay       = 0
};


static nrf_pwm_values_common_t /*const*/ seq1_values[] =
{
         DUTY_B,DUTY_B,DUTY_B,DUTY_B,DUTY_B,DUTY_B,DUTY_B
};

nrf_pwm_sequence_t const seq1 =
{
    .values.p_common = seq1_values,
    .length          = NRF_PWM_VALUES_LENGTH(seq1_values),
    .repeats         = 36,
    .end_delay       = 0
};


static void pwm_init(void)
{
    nrf_drv_pwm_config_t const config0 =
    {
        .output_pins =
        {
            OUTPUT_PIN, // 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_1MHz,
        .count_mode   = NRF_PWM_MODE_UP,
        .top_value    = 100,
        .load_mode    = NRF_PWM_LOAD_COMMON,
        .step_mode    = NRF_PWM_STEP_AUTO
    };
    // Init PWM without error handler
    APP_ERROR_CHECK(nrf_drv_pwm_init(&m_pwm0, &config0, NULL));
    
}


int main(void)
{

    // Start clock for accurate frequencies
    NRF_CLOCK->TASKS_HFCLKSTART = 1; 
    // Wait for clock to start   
    while(NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);   
    
    pwm_init();

   APP_ERROR_CHECK(nrf_drv_pwm_complex_playback(&m_pwm0, &seq0, &seq1, 1,
                                       NRF_DRV_PWM_FLAG_LOOP ));

    while(true)
    {
    __WFE();
    __SEV();
    __WFE();

    }
}


/** @} */