How to correct the sampling time?

[Ted]

Dear everyone,

My platform is SDK16 and IDE is KEIL V5.25.

I set timer 2 to 104uS to sample a serial data. It isn't UART data, no start bit and stop bit.The start bytes are 0x55,0x55,0x01,0x01. But The sample time and data rate aren't very match. It cannot sample data correctly as attach picture. The function of tda5235_sample_handler is for correcting the sample time at falling edge of RX data. But it seems ineffective. I use a gpio of TDA5235B_SS_PIN (toggle it)  to debug the sample time. Could anyone guide me how to correct the sample time?

void m_timer2_event_handler(nrf_timer_event_t event_type, void *p_context)
{
    if (lf_rf_task.items.rssi_valid)
    {
        if (lf_rf_task.items.sync_rx == 1)
        {
            lf_rf_task.sample_rx_buf[lf_rf_task.sample_rx_len] &= ~1;
            nrf_gpio_pin_toggle(TDA5235B_SS_PIN);
            if (nrf_gpio_pin_read(TDA5235A_PP1_PIN))
                lf_rf_task.sample_rx_buf[lf_rf_task.sample_rx_len] |= 1;
            if (++lf_rf_task.sample_rx_bit >= 8)
            {
                lf_rf_task.sample_rx_bit = 0;
                if (++lf_rf_task.sample_rx_len >= 9)
                {
                    lf_rf_task.items.sync_rx = 0;
                    lf_rf_task.items.sample_rx_valid = 1;
                }
            }
            else
            {
                lf_rf_task.sample_rx_buf[lf_rf_task.sample_rx_len] <<= 1;
                lf_rf_task.items.sync_rx = 1;
            }
        }
        else
        {
            rrrr &= ~1;
            nrf_gpio_pin_toggle(TDA5235B_SS_PIN);
            if (nrf_gpio_pin_read(TDA5235A_PP1_PIN))
                rrrr |= 1;
            if (++lf_rf_task.sample_rx_bit >= 24)
            {
                if ((rrrr & 0xffffff) == 0x550101)
                {
                    // sync received
                    lf_rf_task.sample_rx_len = 0;
                    lf_rf_task.sample_rx_bit = 0;
                    lf_rf_task.items.sync_rx = 1;
                }
                else
                {
                    rrrr <<= 1;
                    lf_rf_task.sample_rx_bit--;
                }
            }
        }
    }
    else
    {
        // rssi just under threshole, clear counter
        lf_rf_task.items.sync_rx = 0;
    }
    nrf_drv_saadc_sample();
}

void tda5235_sample_handler(nrf_drv_gpiote_pin_t pin, nrf_gpiote_polarity_t action)
{
    NRF_TIMER2->TASKS_COUNT = 100; //  it is ineffective.
}

static void tda5235_gpio_init(void)
{
    ret_code_t err_code;

    nrf_gpio_cfg_input(TDA5235A_PP1_PIN, NRF_GPIO_PIN_PULLUP);
    nrf_gpio_cfg_input(TDA5235A_PP2_PIN, NRF_GPIO_PIN_PULLUP);

    nrf_drv_gpiote_in_config_t in_config = GPIOTE_CONFIG_IN_SENSE_HITOLO(true);
    in_config.pull = NRF_GPIO_PIN_PULLUP;
    err_code = nrf_drv_gpiote_in_init(TDA5235A_PP2_PIN, &in_config, tda5235_int_handler);
    APP_ERROR_CHECK(err_code);
    nrf_drv_gpiote_in_event_enable(TDA5235A_PP2_PIN, true);

    // for data sample correction
    err_code = nrf_drv_gpiote_in_init(TDA5235A_PP1_PIN, &in_config, tda5235_sample_handler);
    APP_ERROR_CHECK(err_code);
    nrf_drv_gpiote_in_event_enable(TDA5235A_PP1_PIN, true);
}

[Ted]

Susheel Nuguru The unit of timer library is in mini-second. I cannot use timer library, because my sample time is 104uS. It more faster than the functions they was provided by timer library. I change TIMER2->CC register and set it back to 0x680 (104uS) for next sampling. The data still cannot be read correctly. Do you have any suggestions?

void tda5235_sample_handler(nrf_drv_gpiote_pin_t pin, nrf_gpiote_polarity_t action)
{
NRF_TIMER2->CC[0] = 0x240;     // --> correct time, after falling edge of data.
NRF_TIMER2->TASKS_CLEAR = 1;
lf_rf_task.items.rewrite_sample_time = 1;
}

void m_timer2_event_handler(nrf_timer_event_t event_type, void* p_context)
{
if(lf_rf_task.items.rewrite_sample_time == 1)
{
NRF_TIMER2->CC[0] = 0x680;   //set it back to 0x680 (104uS)
NRF_TIMER2->TASKS_CLEAR = 1;
lf_rf_task.items.rewrite_sample_time = 0;
......

}