#define SAMPLES_IN_BUFFER 1
static nrf_saadc_value_t     m_buffer_pool[2][SAMPLES_IN_BUFFER];

void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
    if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
    {
	uint16_t  adc_result;
	uint8_t   adc_result_notify;
	uint16_t  adc_lvl_in_milli_volts;
	uint16_t  batt_lvl_in_milli_volts;
	uint32_t  err_code;
        int i;
        for (i = 0; i < SAMPLES_IN_BUFFER; i++)
        {
            NRF_LOG_INFO("%d", p_event->data.done.p_buffer[i]);
        }
	//calculate some sac value.
	adc_result = p_event->data.done.p_buffer[0];
	adc_lvl_in_milli_volts = ADC_RESULT_IN_MILLI_VOLTS(adc_result);
	NRF_LOG_INFO("adc_lvl:%d",adc_lvl_in_milli_volts);
        batt_lvl_in_milli_volts = BATTERY_IN_MILLI_VOLTS(adc_lvl_in_milli_volts);
	NRF_LOG_INFO("batt_lvl:%d",batt_lvl_in_milli_volts);
	adc_result_notify = (batt_lvl_in_milli_volts - MIN_MILLI_VOLTS) / PERCENT_MILLI_VOLTS;
        err_code = ble_bas_battery_level_update(&m_bas, adc_result_notify);
	NRF_LOG_INFO("battery err_code:%d",err_code);
        if ((err_code != NRF_SUCCESS) &&
        (err_code != NRF_ERROR_BUSY) &&
        (err_code != NRF_ERROR_RESOURCES) &&
        (err_code != NRF_ERROR_FORBIDDEN) &&
        (err_code != NRF_ERROR_INVALID_STATE) &&
        (err_code != BLE_ERROR_GATTS_SYS_ATTR_MISSING))
	{
		APP_ERROR_HANDLER(err_code);
	}
	err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);
        APP_ERROR_CHECK(err_code);
}

void saadc_init(void)
{
    ret_code_t err_code;
    nrf_saadc_channel_config_t channel_config =
    NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(SAADC_CH_PSELP_PSELP_AnalogInput3); //SAADC_CH_PSELP_PSELP_VDD

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

    err_code = nrf_drv_saadc_channel_init(0, &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);
}

static void bsp_event_handler(bsp_event_t event)	
{
	...
	case	BSP_EVENT_ADVERTISING_START:
		err_code = nrf_drv_saadc_sample();
		APP_ERROR_CHECK(err_code);
		...
	...
}