Frequency not read for nrfx PWM peripheral in WaveForm mode

RE: Frequency not read for nrfx PWM peripheral in WaveForm mode

Jared — Fri, 20 Aug 2021 08:34:56 GMT

Hi,

Attached is the complete project. Build and flash it to your nRF5340 and see if you can measure the signal on pin P0.04.

regards

Jared

devzone.nordicsemi.com/.../ncs_5F00_pwm.7z

RE: Frequency not read for nrfx PWM peripheral in WaveForm mode

JonasForssell — Wed, 18 Aug 2021 12:53:20 GMT

Very interesting!

This program does not output anything on pin 0.04 for me and the LED is still blinking with a strange duty cycle at 1000Hz. It complies fine.

Are there any particular build options I should enable perhaps in the project which I have missed?
If i go to project and select "Configure nrf Connect SDK Project" - select menuconfig, I can see that both GPIO drivers and PWM drivers are selected.

As an additional information, I can control any pin - everything works as expected - when I bypass the drivers all together and program the hardware directly.

/Jonas

RE: Frequency not read for nrfx PWM peripheral in WaveForm mode

Jared — Wed, 18 Aug 2021 07:42:27 GMT

#include <stdio.h>
#include <string.h>
#include <nrfx_pwm.h>
#include <zephyr.h>

// Use Zephyr macro to get access to the LED0 on the board
//#define OUTPUT_PIN DT_GPIO_PIN(DT_ALIAS(led0), gpios)

// Use nrfx to create a PWM instance which we will connect to the LED0 later
static nrfx_pwm_t m_pwm0 = NRFX_PWM_INSTANCE(0);

// Declare variables holding PWM sequence values. In this example only one channel is used 
// We start off with a counter to 50 and a top value of 100 giving a 50% duty cyle.
nrf_pwm_values_wave_form_t seq_values[] = {50, 0, 0, 100};

nrf_pwm_sequence_t const seq =
{
    .values.p_wave_form = seq_values,
    .length          = NRF_PWM_VALUES_LENGTH(seq_values),
    .repeats         = 0,
    .end_delay       = 0
};


nrfx_pwm_config_t const config0 =
    {
        .output_pins =
        {
            4,                        // channel 0 now connected to LED0
            NRFX_PWM_PIN_NOT_USED,             // channel 1
            NRFX_PWM_PIN_NOT_USED,             // channel 2
            NRFX_PWM_PIN_NOT_USED,             // channel 3
        },
        .irq_priority = NRFX_PWM_DEFAULT_CONFIG_IRQ_PRIORITY,
        .base_clock   = NRF_PWM_CLK_1MHz,       // Here we select which prescaler to use
        .count_mode   = NRF_PWM_MODE_UP,
        .top_value    = 100,                    // This is ignored when in wave form mode
        .load_mode    = NRF_PWM_LOAD_WAVE_FORM,
        .step_mode    = NRF_PWM_STEP_AUTO
    };

int main(void) {

// Init PWM without error handler
nrfx_pwm_init(&m_pwm0, &config0, NULL, NULL);

// Set and start
nrfx_pwm_simple_playback(&m_pwm0, &seq, 1, NRFX_PWM_FLAG_LOOP);

while(1) 
    k_msleep(3000);

}

RE: Frequency not read for nrfx PWM peripheral in WaveForm mode

JonasForssell — Wed, 18 Aug 2021 06:53:32 GMT

Thank you for your reply Jared.
Would you mind posting your modified code that you tried so that I can replicate this on my board and oscilloscope?

I have measured the PWM signal on pin 28 which also is connected to the LED.

RE: Frequency not read for nrfx PWM peripheral in WaveForm mode

Jared — Tue, 17 Aug 2021 09:06:00 GMT

Hi there!

I tried your example on my nRF5340 DK, the only change I did was to change the pin to P0.04 so that I could probe the signal with my logic analyzer. As you can see from trace, it actually produces a 10 kHz signal. How did you measure your signal?

Maybe I misunderstood your problem?

regards

Jared