Sending SAADC Data via Bluetooth in nrf52832

[Masoumeh]

Hi, 

Hope you are well. 

I want to send the saadc data with ble to my pc. I used the below code. I am getting the data in the right format but  i am loosing some data in the process. I need a sampling frequency more than 20kHz for my work. can you help me to understand why I am loosing some data? I think that the problem is due to the saadc_samplin_event_init() function. I did not change any of the configuration for this part and it is the same as the saadc example in sdk17. 

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#include <stdbool.h>
#include <stdint.h>
#include <string.h>
#include "sdk_common.h"
#include "nrf.h"
#include "nrf_esb.h"
#include "nrf_error.h"
#include "nrf_esb_error_codes.h"
#include "nrf_delay.h"
#include "nrf_gpio.h"
#include "nrf_clock.h"
#include "boards.h"
#include "nrf_delay.h"
#include "app_util.h"

/** user's code begins 1. 
*/
#include <stdio.h>
#include "nrf_drv_saadc.h"
#include "nrf_drv_ppi.h"
#include "nrf_drv_timer.h"
#include "app_error.h"
#include "app_util_platform.h"
#include "nrf_pwr_mgmt.h"
/** user's code ends 1. 
*/

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

/** user's code begins 2. 
*/

#define SAMPLES_IN_BUFFER 15
volatile uint8_t state = 1;

static const nrf_drv_timer_t m_timer = NRF_DRV_TIMER_INSTANCE(0);
static nrf_saadc_value_t     m_buffer_pool[2][SAMPLES_IN_BUFFER];
static nrf_ppi_channel_t     m_ppi_channel;
static uint32_t              m_adc_evt_counter;

static nrf_esb_payload_t        tx_payload = NRF_ESB_CREATE_PAYLOAD(0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00);
static nrf_esb_payload_t        rx_payload;
uint8_t flag=0;

void timer_handler(nrf_timer_event_t event_type, void * p_context)
{

}

void saadc_sampling_event_init(void)
{
    ret_code_t err_code;

    err_code = nrf_drv_ppi_init();
    APP_ERROR_CHECK(err_code);

    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    timer_cfg.bit_width = NRF_TIMER_BIT_WIDTH_32;
    err_code = nrf_drv_timer_init(&m_timer, &timer_cfg, timer_handler);
    APP_ERROR_CHECK(err_code);

    /* setup m_timer for compare event every 400ms */
    uint32_t ticks = nrf_drv_timer_ms_to_ticks(&m_timer, 400);
    nrf_drv_timer_extended_compare(&m_timer,
                                   NRF_TIMER_CC_CHANNEL0,
                                   ticks,
                                   NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
                                   false);
    nrf_drv_timer_enable(&m_timer);

    uint32_t timer_compare_event_addr = nrf_drv_timer_compare_event_address_get(&m_timer,
                                                                                NRF_TIMER_CC_CHANNEL0);
    uint32_t saadc_sample_task_addr   = nrf_drv_saadc_sample_task_get();

    /* setup ppi channel so that timer compare event is triggering sample task in SAADC */
    err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_ppi_channel_assign(m_ppi_channel,
                                          timer_compare_event_addr,
                                          saadc_sample_task_addr);
    APP_ERROR_CHECK(err_code);
}


void saadc_sampling_event_enable(void)
{
    ret_code_t err_code = nrf_drv_ppi_channel_enable(m_ppi_channel);

    APP_ERROR_CHECK(err_code);
}


void saadc_callback(nrf_drv_saadc_evt_t const * p_event) //ok
{
    if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
    {
        ret_code_t err_code;

        err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);
        APP_ERROR_CHECK(err_code);

        int i;
			
				for (i = 0; i < SAMPLES_IN_BUFFER; i++)
			  {
					tx_payload.data[i*2+1] =  (uint8_t)(p_event->data.done.p_buffer[i]);
					tx_payload.data[(i*2)+2] = (uint8_t)(p_event->data.done.p_buffer[i] >> 8);
			  }
				tx_payload.data[0]=m_adc_evt_counter++;
				nrf_esb_write_payload(&tx_payload);
    }
}


void saadc_init(void) //ok
{
    ret_code_t err_code;
    nrf_saadc_channel_config_t channel_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN4);

    err_code = nrf_drv_saadc_init(NULL, saadc_callback);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_channel_init(4, &channel_config);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);
		
		nrf_saadc_continuous_mode_enable(80);

}

/** user's code ends 2. 
*/


void nrf_esb_event_handler(nrf_esb_evt_t const * p_event)
{
    switch (p_event->evt_id)
    {
        case NRF_ESB_EVENT_TX_SUCCESS:
            NRF_LOG_DEBUG("TX SUCCESS EVENT");
            break;
        case NRF_ESB_EVENT_TX_FAILED:
            NRF_LOG_DEBUG("TX FAILED EVENT");
            (void) nrf_esb_flush_tx();
            (void) nrf_esb_start_tx();
            break;
        case NRF_ESB_EVENT_RX_RECEIVED:
            NRF_LOG_DEBUG("RX RECEIVED EVENT");
            while (nrf_esb_read_rx_payload(&rx_payload) == NRF_SUCCESS)
            {
                if (rx_payload.length > 0)
                {
                    NRF_LOG_DEBUG("RX RECEIVED PAYLOAD");
                }
            }
            break;
    }
}


void clocks_start( void )
{
    NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
    NRF_CLOCK->TASKS_HFCLKSTART = 1;

    while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);
}


void gpio_init( void )
{
    nrf_gpio_range_cfg_output(8, 15);
    bsp_board_init(BSP_INIT_LEDS);
}


uint32_t esb_init( void )
{
    uint32_t err_code;
    uint8_t base_addr_0[4] = {0xE7, 0xE7, 0xE7, 0xE7};
    uint8_t base_addr_1[4] = {0xC2, 0xC2, 0xC2, 0xC2};
    uint8_t addr_prefix[8] = {0xE7, 0xC2, 0xC3, 0xC4, 0xC5, 0xC6, 0xC7, 0xC8 };

    nrf_esb_config_t nrf_esb_config         = NRF_ESB_DEFAULT_CONFIG;
    nrf_esb_config.protocol                 = NRF_ESB_PROTOCOL_ESB_DPL;
    nrf_esb_config.retransmit_delay         = 600;
    nrf_esb_config.bitrate                  = NRF_ESB_BITRATE_2MBPS;
    nrf_esb_config.event_handler            = nrf_esb_event_handler;
    nrf_esb_config.mode                     = NRF_ESB_MODE_PTX;
    nrf_esb_config.selective_auto_ack       = false;

    err_code = nrf_esb_init(&nrf_esb_config);

    VERIFY_SUCCESS(err_code);

    err_code = nrf_esb_set_base_address_0(base_addr_0);
    VERIFY_SUCCESS(err_code);

    err_code = nrf_esb_set_base_address_1(base_addr_1);
    VERIFY_SUCCESS(err_code);

    err_code = nrf_esb_set_prefixes(addr_prefix, NRF_ESB_PIPE_COUNT);
    VERIFY_SUCCESS(err_code);

    return err_code;
}


int main(void)
{
	
    ret_code_t err_code;
    gpio_init();
  	nrf_gpio_pin_clear(10);

    err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();
	
  	nrf_gpio_cfg_output(27);
		nrf_gpio_pin_clear(27);
	
	
		clocks_start();
	
    err_code = esb_init();
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEBUG("Enhanced ShockBurst Transmitter Example started.");
		
		/** user's code begins 3. 
		*/
		ret_code_t ret_code = nrf_pwr_mgmt_init();
    APP_ERROR_CHECK(ret_code);

    saadc_init();
    saadc_sampling_event_init();
    saadc_sampling_event_enable();
    NRF_LOG_INFO("SAADC HAL simple example started.");	
		nrf_drv_saadc_sample();
		/** usr's code ends 3. 
		*/ 
    while (true)
    { 
				nrf_pwr_mgmt_run();
				NRF_LOG_FLUSH();				
    }
}

[ovrebekk]

Hi 

Do you ever see the NRF_ESB_EVENT_TX_FAILED event occur, or that the call to nrf_esb_write_payload(..) returns an error?

If you are uploading data to the nrf_esb library faster than it is able to send it out, you will at some point fill up the buffers, and if you ignore this error it will lead to packet loss. 

One way to increase data throughput is to increase the size of each packet (on the nRF52 series you can go up to 252 bytes payload), but this will only work if you have nRF52 devices on both sides of the link. 

Best regards
Torbjørn

[Masoumeh]

I am using the nrf24l01+ as the receiver and its packet load is 32 bytes max. so what can be my sampling frequency with these system while my radio is working in 2Mbits/s and my resolution for adc is 12 bits, also i put every 2 samples of the adc in 3 byte of the packet load to optimize the configuration. 

[ovrebekk]

Hi 

I don't think we have done much benchmarking to see how fast you can send packets from an nRF52 device to the nRF24L01+, but it should be possible to send at least one packet every 500us, which corresponds to about 40kHz sampling frequency in your case. 

Just keep in mind that this assumes zero packet loss, and that the data is sent and read out efficiently on both sides of the link. 

As I mentioned earlier it is critical to observe the nrf_esb_write_payload(..) return code and the frequency of NRF_ESB_EVENT_TX_FAILED events in order to see if the data is successfully transferred to the PRX device. 

Best regards
Torbjørn