using pwm input to measure frequency

[Timothy]

I have an NRF9160 system running and I see mention of "The nRF9160 PWM peripheral can capture the period and pulse width of an external PWM signal" but  was a little confused as to how to implement it. I have used and I am using PWM as an output so that I understand. I have used a generic GPIO as input and used interrupts to start and stop a timer to measure time between edges. This uses two items a generic GPIO and a timer. as I understand the capture capability it just used a single PWM to do the measurement.

can you point me to any examples how to implement this if I am correct in assuming all I need is a single PWM pin.

[Timothy]

I have the 1 usec timer working. 

[Susheel Nuguru]

Thanks for lettings us know Timothy, if possible please post the solution here so that it could help others aswell. The code I posted compiled fine at my end, but I am not sure what your complete setup is.

[Timothy]

Fullscreen myTimer.c Download

#include <nrfx_timer.h>

#if 1

#define TIMER_ID 1
static const nrfx_timer_t timer = NRFX_TIMER_INSTANCE(TIMER_ID);

static void on_timer_event(nrf_timer_event_t evt, void *ctx) {}

void init_us_timer(void)
{

    nrfx_timer_config_t cfg = NRFX_TIMER_DEFAULT_CONFIG(1000000);
//    nrfx_timer_config_t cfg = NRFX_TIMER_DEFAULT_CONFIG(16000000);
//    cfg.frequency = NRF_TIMER_FREQ_1MHz;
    cfg.mode = NRF_TIMER_MODE_TIMER;
    cfg.bit_width = NRF_TIMER_BIT_WIDTH_32;

uint32_t status = nrfx_timer_init(&timer, &cfg, on_timer_event);
__ASSERT_NO_MSG(status == NRFX_SUCCESS);
    nrfx_timer_enable(&timer);
}

uint32_t get_us_count(void)
{
    return nrfx_timer_capture_get(&timer, NRF_TIMER_CC_CHANNEL0);
}

uint32_t capture_us(void)
{
    nrfx_timer_capture(&timer, NRF_TIMER_CC_CHANNEL0);
    return get_us_count();
}

void clear_us(void)
{
    nrfx_timer_clear(&timer);
    return;
}
#endif

I used the attached file. my interrupt handler for GPIO 09 is as follows. this is as minimum as I could get it.

 

uint32_t nrfxCount = NRFX_COUNTER_ARRAY_SIZE;

uint32_t nrfxCountArray[NRFX_COUNTER_ARRAY_SIZE];

 

void gpio09Callback(struct device *dev, struct gpio_callback *cb, uint32_t pins)

{

    if (nrfxCount < NRFX_COUNTER_ARRAY_SIZE)

    {

        nrfxCountArray[nrfxCount++] = capture_us();

    }

   }

the simple test program is as follows

   struct gpio_callback gpio_09_cb;

    init_us_timer();

    k_sleep(K_SECONDS(1));

    gpio_init_callback(&gpio_09_cb, (gpio_callback_handler_t)gpio09Callback, BIT(GPIO_09_DEV_PIN));

    gpio_add_callback(gpio_09_dev, &gpio_09_cb);

    gpio_pin_interrupt_configure(gpio_09_dev, GPIO_09_DEV_PIN, GPIO_INT_ENABLE | GPIO_INT_EDGE | GPIO_INT_EDGE_RISING);

    printf("Start GPIO_09 Interrupt test\r\n");

    nrfxCount = 0;

    while (1)

    {

        if (nrfxCount >= NRFX_COUNTER_ARRAY_SIZE)

        {

            for (int j = 1; j < NRFX_COUNTER_ARRAY_SIZE; j++)

            {

                 printk("GPIO_09 %d\tcounts:%d\tsec: %3.5e\tfreq: %3.3e\r\n", j, (nrfxCountArray[j] - nrfxCountArray[j - 1]),

                       (nrfxCountArray[j] - nrfxCountArray[j - 1]) / NRFX_COUNTER_FREQ,

                       1 / ((nrfxCountArray[j] - nrfxCountArray[j - 1]) / NRFX_COUNTER_FREQ));

                k_sleep(K_MSEC(200));

            }

            printk("\r\n");

            k_sleep(K_SECONDS(1));

            nrfxCount = 0;

        }

        k_sleep(K_SECONDS(1));

    }

NOTES: !!!

this measures the frequency well up to about 30 kHz. I am setting the timer frequency to 16 MHz to get the most counts (accuracy). It does not work at all past that. anything past 60 kHz reads as ~65 kHz. I need to be able to measure a frequency of up to 150 kHz. this solution cannot do that. The interrupt handler looks like it takes about 20 usec so I miss counts when the period is < 20 usec. the interrupt handler needs to be on the order of 5 usec in order to count 150 kHz (6.67 usec).

How can I get the timer to measue frequencies up to 150 kHz?

[Timothy]

How can I assure that the GPIO 09 pin has the highest priority and is handle in the fastest way.

[Susheel Nuguru]

You cannot set the interrupt priority of the pin handling itself but you can set the priority of interrupt handler for GPIO driver. The priority is handled with NRFX_DEFAULT_IRQ_PRIORITY in modules\hal\nordic\nrfx\templates\nrfx_config_nrf91.h