How to get pulse time with microsecond level?

[Taylor]

Hi Nordic,

I need to read pulse time which is microsecond level in different channel, I have consider combining timers with GPIOE but the timer is millisecond level. Is there any example to achieve it?

BTW, I'm using SDK17.02 on nRF52810.

[qwertynoon]

Hi. Share your timer init part of code please.

[Taylor]

I'm using HID demo in SDK17.02. 

static void timers_init(void)
{
    ret_code_t err_code;

    err_code = app_timer_init();
    APP_ERROR_CHECK(err_code);

    // Create battery timer.
    err_code = app_timer_create(&m_battery_timer_id,
                                APP_TIMER_MODE_REPEATED,
                                battery_level_meas_timeout_handler);
    APP_ERROR_CHECK(err_code);
}

And the APP_TIMER_TICKS(xx) is millisecond level.

[qwertynoon]

static const nrfx_timer_t micros_sample_timer = NRFX_TIMER_INSTANCE(4); //select timer instance

uint32_t micros;

static void micros_timer_handler(nrf_timer_event_t event_type, void * p_context)
{
    micros++;
}

static int timer_init_micros(void)
{
    nrfx_err_t err;
    nrfx_timer_config_t timer_cfg = {
        .frequency = NRF_TIMER_FREQ_16MHz,
        .mode = NRF_TIMER_MODE_TIMER,
        .bit_width = NRF_TIMER_BIT_WIDTH_32,
    };

    err = nrfx_timer_init(&micros_sample_timer, &timer_cfg, micros_timer_handler);
    if (err != NRFX_SUCCESS) {
        LOG_INF("nrfx_timer_init failed with: %d\n", err);
        return -EAGAIN;
    }
/* For Zephyr*/
/*
    IRQ_CONNECT(DEFAULT_TIMER_IRQ, DEFAULT_TIMER_PRIORITY,
            DEFAULT_TIMER_IRQ_HANDLER, NULL, 0);
*/

    nrfx_timer_extended_compare(&micros_sample_timer,
            NRF_TIMER_CC_CHANNEL4,
            nrfx_timer_us_to_ticks(&micros_sample_timer, 1), // 1 us tic
            NRF_TIMER_SHORT_COMPARE4_CLEAR_MASK,
            true);

    nrfx_timer_enable(&micros_sample_timer);

    return 0;
}

use micros for pulse period calc

[Susheel Nuguru]

The app timer tick frequency depends on the config you set in sdk_config.h (APP_TIMER_CONFIG_RTC_FREQUENCY). If you set it to 0 you get the max tick rate of 32768 ticks per seconds which equals about 30.5us per tick.

You cannot use any ticks less than 5 in app_timer_start, so the shortest delay you can get is around 152.5us. Getting smaller than that using app_timer is not possible. You should try to use high frequency TIMERS instead for that.