NRF52840 SPIM3 extended config ss_duration not changing CSN inactive duration?

Question

By changing ss_duration the duration CSN is high doesn't seem to be effected?

ss_duration = 2

CSN

SCK

ss_duration = 64

CSN

SCK

Setup

SPI Config

#define SS_DURATION_SHORT 2
#define SS_DURATION_LONG 64

nrfx_spim_config_t spi_config = NRFX_SPIM_DEFAULT_CONFIG;
spi_config.ss_pin = DEVICE_CS;
spi_config.miso_pin = SPI_MISO;
spi_config.mosi_pin = NRFX_SPIM_PIN_NOT_USED;
spi_config.sck_pin = SPI_SCK;
spi_config.ss_active_high = false;
spi_config.frequency = NRF_SPIM_FREQ_1M;
spi_config.mode = NRF_SPIM_MODE_0;
spi_config.bit_order = NRF_SPIM_BIT_ORDER_MSB_FIRST;
spi_config.dcx_pin = NRFX_SPIM_PIN_NOT_USED;
spi_config.use_hw_ss = true;
spi_config.ss_duration = SS_DURATION_SHORT;

nrfx_spim_init(&spi, &spi_config, NULL, NULL);

spi.p_reg->RXD.PTR = (uint32_t)sample_buffer;
spi.p_reg->RXD.MAXCNT = sizeof(sample_buffer[0]); //Size of transaction
spi.p_reg->RXD.LIST = 1; //Use ARRAY List

PPI

SPIM3 END EVENT -> SPIM3 START TASK

SPIM3 END EVENT -> TIMER2 COUNT TASK

Example Code Below

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/** @file
 *
 * @defgroup blinky_example_main main.c
 * @{
 * @ingroup blinky_example
 * @brief Blinky Example Application main file.
 *
 * This file contains the source code for a sample application to blink LEDs.
 *
 */

#include <stdbool.h>
#include <stdint.h>
#include "nrf_delay.h"

//Nordic
#include "nrf_gpio.h"
#include "nrfx_spim.h"
#include "nrfx_timer.h"
#include "nrfx_ppi.h"
#include "nrf_drv_ppi.h"

#define SAMPLES 1001
#define SAMPLE_BUFFER_SIZE SAMPLES + 100

static uint8_t sample_buffer[SAMPLE_BUFFER_SIZE][3];
static volatile uint32_t sample_buffer_count = 0;

static const nrfx_spim_t spi = NRFX_SPIM_INSTANCE(3);
static const nrfx_timer_t count_timer = NRFX_TIMER_INSTANCE(2);

static nrf_ppi_channel_t spi_start_ppi_channel;
static nrf_ppi_channel_t spi_sample_ppi_channel;
static nrf_ppi_channel_t spi_count_ppi_channel;

#define DEVICE_CS NRF_GPIO_PIN_MAP(1,10)
#define SPI_MISO NRF_GPIO_PIN_MAP(1,11)
#define SPI_SCK NRF_GPIO_PIN_MAP(0,28)

#define SS_DURATION_SHORT 2
#define SS_DURATION_LONG 64

static void start() {
  //Enable sample looping channel
  nrf_drv_ppi_channel_enable(spi_sample_ppi_channel);

  //Reset pointer
  spi.p_reg->RXD.PTR = (uint32_t)sample_buffer;

  nrf_spim_task_trigger(spi.p_reg, NRF_SPIM_TASK_START);
}

static void timer_handler(nrf_timer_event_t event_type, void * p_context) {

}


static volatile uint32_t sample_buffer_count;

/**
 * @brief Function for application main entry.
 */
int main(void)
{
  nrf_gpio_cfg_output(DEVICE_CS);
  nrf_gpio_cfg_output(SPI_SCK);
  nrf_gpio_cfg_input(SPI_MISO, NRF_GPIO_PIN_NOPULL);

  nrfx_spim_config_t spi_config = NRFX_SPIM_DEFAULT_CONFIG;
  spi_config.ss_pin         = DEVICE_CS;
  spi_config.miso_pin       = SPI_MISO;
  spi_config.mosi_pin       = NRFX_SPIM_PIN_NOT_USED;
  spi_config.sck_pin        = SPI_SCK;
  spi_config.ss_active_high = false;
  spi_config.frequency      = NRF_SPIM_FREQ_1M;
  spi_config.mode           = NRF_SPIM_MODE_0;
  spi_config.bit_order      = NRF_SPIM_BIT_ORDER_MSB_FIRST;
  spi_config.dcx_pin = NRFX_SPIM_PIN_NOT_USED;
  spi_config.use_hw_ss = true;
  spi_config.ss_duration = SS_DURATION_LONG;

  nrfx_spim_init(&spi, &spi_config, NULL, NULL);

  spi.p_reg->RXD.PTR = (uint32_t)sample_buffer;
  spi.p_reg->RXD.MAXCNT = sizeof(sample_buffer[0]); //Size of transaction
  spi.p_reg->RXD.LIST = 1; //Use ARRAY List

  uint32_t err_code = nrf_drv_ppi_init();


  //Sample
  err_code = nrf_drv_ppi_channel_alloc(&spi_sample_ppi_channel);
  APP_ERROR_CHECK(err_code);
  
  uint32_t spi_end_evt_addr        = nrfx_spim_end_event_get(&spi);
  uint32_t spi_start_task_addr       = nrfx_spim_start_task_get(&spi);

  //Trigger SPI start on a SPI end
  err_code = nrf_drv_ppi_channel_assign(spi_sample_ppi_channel, spi_end_evt_addr, spi_start_task_addr);
  APP_ERROR_CHECK(err_code);
  
  err_code = nrf_drv_ppi_channel_enable(spi_sample_ppi_channel);
  APP_ERROR_CHECK(err_code);



  //Count
  //Setup timer in counter mode
  nrfx_timer_config_t timer_cfg = NRFX_TIMER_DEFAULT_CONFIG;
  timer_cfg.frequency = NRF_TIMER_FREQ_16MHz;
  timer_cfg.bit_width = NRF_TIMER_BIT_WIDTH_32;
  timer_cfg.mode = NRF_TIMER_MODE_LOW_POWER_COUNTER;

  err_code = nrfx_timer_init(&count_timer, &timer_cfg, timer_handler);

  

  //Count PPI
  err_code = nrf_drv_ppi_channel_alloc(&spi_count_ppi_channel);
  APP_ERROR_CHECK(err_code);

  uint32_t timer_count_evt_addr       = nrfx_timer_task_address_get(&count_timer, NRF_TIMER_TASK_COUNT);

  err_code = nrf_drv_ppi_channel_assign(spi_count_ppi_channel, spi_end_evt_addr, timer_count_evt_addr);
  APP_ERROR_CHECK(err_code);
  
  err_code = nrf_drv_ppi_channel_enable(spi_count_ppi_channel);
  APP_ERROR_CHECK(err_code);


  //Start Sampling
  start();


  while(true) {

    nrfx_timer_capture(&count_timer, NRF_TIMER_CC_CHANNEL1);
    sample_buffer_count = nrfx_timer_capture_get(&count_timer, NRF_TIMER_CC_CHANNEL1);

    if(sample_buffer_count >= SAMPLES) {
      //Stop SPI
      nrf_drv_ppi_channel_disable(spi_sample_ppi_channel);

      //Reset counter timer
      nrfx_timer_clear(&count_timer);

      nrf_delay_ms(100);

      //Start Again
      start();
    }

  }

}

/**
 *@}
 **/

Regards,

Jonathan