QDEC doesn't sample fast signals

Question

Hi,

I am using mechanical QDEC which doesn't have LED and simply A and B pins. After going through forum I set the QDEC confguration as follows.

nrf_drv_qdec_config_t qdec_config =
{
	.reportper = NRF_QDEC_REPORTPER_40,             /**< Report period in samples. */
    .sampleper = NRF_QDEC_SAMPLEPER_8192us,         /**< Sampling period in microseconds. */
    .psela = ENC_2_A,                          		/**< Pin number for A input. */
    .pselb = ENC_2_B,                          		/**< Pin number for B input. */
    .pselled = 0xFFFFFFFF,                      	/**< Pin number for LED output. */
    .ledpre = 10,                                   /**< Time (in microseconds) how long LED is switched on before sampling. */
    .ledpol = NRF_QDEC_LEPOL_ACTIVE_LOW,           	/**< Active LED polarity. */
    .dbfen = true,                                  /**< State of debouncing filter. */
    .sample_inten = true,                           /**< Enabling sample ready interrupt. */
    .interrupt_priority = 3,                        /**< QDEC interrupt priority. */
};

Then changed function in nrfx_qdec.c

nrfx_err_t nrfx_qdec_init(nrfx_qdec_config_t const * p_config,
                          nrfx_qdec_event_handler_t  event_handler)

{
...
...
...
    nrf_qdec_sampleper_set(p_config->sampleper);
//    nrf_gpio_cfg_input(p_config->pselled, NRF_GPIO_PIN_NOPULL);
//    nrf_gpio_cfg_input(p_config->psela, NRF_GPIO_PIN_NOPULL);
//    nrf_gpio_cfg_input(p_config->pselb, NRF_GPIO_PIN_NOPULL);
    nrf_qdec_pio_assign(p_config->psela, p_config->pselb, p_config->pselled);
...
...
...
}

Now I am getting values only if encoder is moving very slow and not at normal operation. At normal operation I get m_accread = 1 & m_accdblread = 0 which is incorrect.

Also I get negative value for forward movement and positive for reverse. I have attached proper connections at A and B and also defined them correctly.

Normal operation frequency would be around 2560Hz.

What could possibly go wrong or how to resolve this issue?

SDK 15.2

Regards