The adc-uart sampling is only about 9k.

Question

I am using the SAADC example to check the sampling rate between ADC and UART.

I am using an Arduino serial plotter and logic analyzer to check the correct data.

To check this, the following settings were made.

1 Hz, 3.3 Vp-p

0.nRF52832
Baud rate 1000000
ADC Sampling bit 12bit
Modify the source code to check the optimized Arduino float output value (data [4byte] + newline character [2byte] = 6byte)

Source code

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/** @file
 * @defgroup nrf_adc_example main.c
 * @{
 * @ingroup nrf_adc_example
 * @brief ADC Example Application main file.
 *
 * This file contains the source code for a sample application using ADC.
 *
 * @image html example_board_setup_a.jpg "Use board setup A for this example."
 */

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include "nrf.h"
#include "nrf_drv_saadc.h"
#include "nrf_drv_ppi.h"
#include "nrf_drv_timer.h"
#include "boards.h"
#include "app_error.h"
#include "nrf_delay.h"
#include "app_util_platform.h"
#include "nrf_pwr_mgmt.h"

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

#define SAMPLES_IN_BUFFER 1
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;


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_us_to_ticks(&m_timer, 110);
    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)
{
    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;
        //NRF_LOG_INFO("ADC event number: %d", (int)m_adc_evt_counter);

        for (i = 0; i < SAMPLES_IN_BUFFER; i++)
        {
            NRF_LOG_RAW_INFO("%d\n", p_event->data.done.p_buffer[i]);
        }
        m_adc_evt_counter++;
    }
}


void saadc_init(void)
{
    ret_code_t err_code;
    nrf_saadc_channel_config_t channel_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);

    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);

}


/**
 * @brief Function for main application entry.
 */
int main(void)
{
    uint32_t err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();

    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.");

    while (1)
    {
        nrf_pwr_mgmt_run();
        NRF_LOG_FLUSH();
    }
}


/** @} */

1. Logic Analyzer

2. Arduino serial plotter

Baud rate 1000000

I have confirmed that data is transmitted well in the sampling cycle of 110us, but it fails in communication at 70us.

Data transmitted normally [sampling cycle 110us]

I want to change the sampling from 110 to 70. (Increase data sampling)

Dropped log out (sampling cycle 70us)

In theory, it turns out a speed of about 20k. (Ignore start/stop bits)
The calculation formula is as follows: 1000000 [Baud rate] / 8[data bit] / 6[char count] = 20,833

I used the following formula to check the number of samples.

Data transmission period (ms) = [sampling time] * [buffer count]
Number of interrupts per second = 1 / [Data transmission period (ms)] * 1000
ADC sampling count = [Number of interrupts per second] * [buffer count]

4606.adc-uart calc.xlsx

Karl Ylvisaker · Accepted Answer

odenwar said: How do you handle the above method? 
 Please keep in mind that I have no prior knowledge of the 'Arduino optimized float' implementation you reference - but it sounds to me like it is just a regular float type (4 bytes) with 2 bytes tacked on at the end, to delimitate the float, is this correct? If so, you expect to send these two static bytes at the end of every float (every sample) you send. If you instead just do not send them, but add them at the receiver side (which might be an arduino?) instead, you save yourself the trouble of sending the two end characters over and over - since they always will be present. So, you just send the 4 meaningful float bytes, and every time the Arduino receives a new float (every 4 bytes), it adds the delimination characters to the end. I might have misunderstood you earlier, and I am unable to find any direct reference to 'Arduino optimized float', so my suggestion might not be applicable. Please let me know if I should elaborate on this, or if any part of my suggestion is unclear. 
 odenwar said: I'll check it out during business hours. 
 Great, I look forward to hearing how it goes! Please also see my earlier suggestion about increasing the sample buffer size. Best regards, Karl

The adc-uart sampling is only about 9k.

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