ESP32ADC采样率配置（基于ESP-IDF）

最近要使用ESP32进行ADC采样，需要对ESP32的ADC采样率进行设置，查阅后发现网上这方面的资料非常少，所以把配置过程写下来以供大家参考

文章目录

一、ESP32的ADC外设

二、示例代码修改

三、ADC采样率获取

四、采样率配置

五、实验验证

六、可能出现的问题

一、ESP32的ADC外设

打开ESP32的技术规格书第34页，可见ESP32具有2个12位的逐次逼近型ADC，他有RTC和DIG两个控制器，其中RTC控制器最大采样率为200KSPS，DIG控制器为2MSPS,如果我们需要采样频率较高的信号，就必须使用DIG控制器。

打开ESP32的技术参考手册第577页找到DIG控制器，可见我们为了追求最大的采样率，应该考虑使用DMA配合ADC使用。

二、示例代码修改

打开ESP-IDF的官方ADC_DMA示例程序，这里我用的是VSCODE+ESP-IDF（v4.4）插件，由于我使用的是ESP32芯片，所以我将所有用于适配其他芯片部分的代码删除，删除后的示例代码如下：

#include <string.h>
#include <stdio.h>
#include "sdkconfig.h"
#include "esp_log.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "freertos/semphr.h"
#include "driver/adc.h"

#define TIMES 1000 //一次的采样点数*2
#define GET_UNIT(x) ((x >> 3) & 0x1)

#if CONFIG_IDF_TARGET_ESP32
#define ADC_RESULT_BYTE 2
#define ADC_CONV_LIMIT_EN 1                  // For ESP32, this should always be set to 1
#define ADC_CONV_MODE ADC_CONV_SINGLE_UNIT_1 // ESP32 only supports ADC1 DMA mode
#define ADC_OUTPUT_TYPE ADC_DIGI_OUTPUT_FORMAT_TYPE1
#endif

#if CONFIG_IDF_TARGET_ESP32
static uint16_t adc1_chan_mask = BIT(7);
static uint16_t adc2_chan_mask = 0;
static adc_channel_t channel[1] = {ADC1_CHANNEL_7}; //设置ADC引脚
#endif

static uint32_t ret_num = 0;
static uint8_t result[TIMES] = {0}; //采样结果存放数组

static const char *TAG = "{adc}";
int countNum;

static void continuous_adc_init(uint16_t adc1_chan_mask, uint16_t 
adc2_chan_mask, adc_channel_t *channel, uint8_t channel_num)
{
    adc_digi_init_config_t adc_dma_config = {
        .max_store_buf_size = 1024,
        .conv_num_each_intr = TIMES,
        .adc1_chan_mask = adc1_chan_mask,
        .adc2_chan_mask = adc2_chan_mask,
    };
    ESP_ERROR_CHECK(adc_digi_initialize(&adc_dma_config));

    adc_digi_configuration_t dig_cfg = {
        .conv_limit_en = ADC_CONV_LIMIT_EN,
        .conv_limit_num = 250,
        .sample_freq_hz = 100000, //采样率
        .conv_mode = ADC_CONV_MODE,
        .format = ADC_OUTPUT_TYPE,
    };

    adc_digi_pattern_config_t adc_pattern[SOC_ADC_PATT_LEN_MAX] = {0};
    dig_cfg.pattern_num = channel_num;
    for (int i = 0; i < channel_num; i++)
    {
        uint8_t unit = GET_UNIT(channel[i]);
        uint8_t ch = channel[i] & 0x7;
        adc_pattern[i].atten = ADC_ATTEN_DB_11; //衰减倍率
        adc_pattern[i].channel = ch;
        adc_pattern[i].unit = unit;
        adc_pattern[i].bit_width = SOC_ADC_DIGI_MAX_BITWIDTH; //采样位数

        // ESP_LOGI(TAG, "adc_pattern[%d].atten is :%x", i, adc_pattern[i].atten);
        //  ESP_LOGI(TAG, "adc_pattern[%d].channel is :%x", i, adc_pattern[i].channel);
        // ESP_LOGI(TAG, "adc_pattern[%d].unit is :%x", i, adc_pattern[i].unit);
    }
    dig_cfg.adc_pattern = adc_pattern;
    ESP_ERROR_CHECK(adc_digi_controller_configure(&dig_cfg));
}

#if !CONFIG_IDF_TARGET_ESP32
static bool check_valid_data(const adc_digi_output_data_t *data)
{
    const unsigned int unit = data->type2.unit;
    if (unit > 2)
        return false;
    if (data->type2.channel >= SOC_ADC_CHANNEL_NUM(unit))
        return false;

    return true;
}
#endif

void app_main(void)
{
    

    memset(result, 0xcc, TIMES);

    continuous_adc_init(adc1_chan_mask, adc2_chan_mask, channel, sizeof(channel) / sizeof(adc_channel_t));
    adc_digi_start();

    
  while(1)
  {
        adc_digi_read_bytes(result, TIMES, &ret_num, ADC_MAX_DELAY);
        for (int i = 0; i < ret_num; i += ADC_RESULT_BYTE)
        {
            adc_digi_output_data_t *p = (void *)&result[i];
            // ESP_LOGI(TAG, "%d", p->type1.data);
            // printf("{value}%d\n", p->type1.data);
            // vTaskDelay(10/ portTICK_PERIOD_MS);
        }
  }
    
}

三、ADC采样率获取

首先ADC的采样率等于单位时间采样的点数，所以需要定义一个变量为countNum，这个变量用于累计单位时间的采样点的个数，把countNum放到ADC采样部分，每完成一次ADC采样就加一，使用freertos中的任务创建函数xTaskCreate(countTask, “countTask”, 1024 * 10, NULL, 2, NULL);，在这个函数中，使用死循环，每间隔一秒打印一次countNum的值，因为这个任务与ADC采样并行运行，所以countNum即为ADC的采样率，代码如下

void countTask(void *param)//创建获取采样率任务
{

    while (1)
    {

        vTaskDelay(1000 / portTICK_PERIOD_MS);
        printf("{count}%d\n", countNum);
        countNum = 0;
    }
}

 adc_digi_read_bytes(result, TIMES, &ret_num, ADC_MAX_DELAY);//ADC采样数据读取
        for (int i = 0; i < ret_num; i += ADC_RESULT_BYTE)
        {
            adc_digi_output_data_t *p = (void *)&result[i];
            value[i] = p->type1.data;

            // ESP_LOGI(TAG, "%d", p->type1.data);
            // printf("{value}%d\n", p->type1.data);
            countNum++;//采样率计数
            // vTaskDelay(10/ portTICK_PERIOD_MS);
        }

四、采样率配置

对ESP32ADC的配置实际上就是对ADC的DIG控制器的配置，在adc.h中可以找到adc_digi_init_config_t和adc_digi_configuration_t结构体的定义，修改这些结构体中的成员就可以改变ADC的相关参数。

typedef struct adc_digi_init_config_s {
    uint32_t max_store_buf_size;    ///< Max length of the converted data that driver can store before they are processed.
    uint32_t conv_num_each_intr;    ///< Bytes of data that can be converted in 1 interrupt.
    uint32_t adc1_chan_mask;        ///< Channel list of ADC1 to be initialized.
    uint32_t adc2_chan_mask;        ///< Channel list of ADC2 to be initialized.
} adc_digi_init_config_t;

typedef struct {
    bool conv_limit_en;                      ///< To limit ADC conversion times. Conversion stops after finishing `conv_limit_num` times conversion
    uint32_t conv_limit_num;                 ///< Set the upper limit of the number of ADC conversion triggers. Range: 1 ~ 255.
    uint32_t pattern_num;                    ///< Number of ADC channels that will be used
    adc_digi_pattern_config_t *adc_pattern;    ///< List of configs for each ADC channel that will be used
    uint32_t sample_freq_hz;  /*!< The expected ADC sampling frequency in Hz. Range: 611Hz ~ 83333Hz
                                   Fs = Fd / interval / 2
                                   Fs: sampling frequency;
                                   Fd: digital controller frequency, no larger than 5M for better performance
                                   interval: interval between 2 measurement trigger signal, the smallest interval should not be smaller than the ADC measurement period, the largest interval should not be larger than 4095 */
    adc_digi_convert_mode_t conv_mode;      ///< ADC DMA conversion mode, see `adc_digi_convert_mode_t`.
    adc_digi_output_format_t format;        ///< ADC DMA conversion output format, see `adc_digi_output_format_t`.
} adc_digi_configuration_t;

我在初始化代码中做出了如下修改
（1）增大max_store_buf_size使得ADC一次可以采集更多的点数
（2）增加TIMES的值，方便观察现象
（3）修改sample_freq_hz，即修改采样率，最大可到达2000000hz

adc_digi_init_config_t adc_dma_config = {
        .max_store_buf_size = 4096,//最大采样缓存
        .conv_num_each_intr = TIMES,
        .adc1_chan_mask = adc1_chan_mask,
        .adc2_chan_mask = adc2_chan_mask,
    };

adc_digi_configuration_t dig_cfg = {
        .conv_limit_en = ADC_CONV_LIMIT_EN,
        .conv_limit_num = 250,
        .sample_freq_hz = 100000, //采样率
        .conv_mode = ADC_CONV_MODE,
        .format = ADC_OUTPUT_TYPE,
    };

最后附上完整代码

#include <string.h>
#include <stdio.h>
#include "sdkconfig.h"
#include "esp_log.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "freertos/semphr.h"
#include "driver/adc.h"

#define TIMES 2000 //一次的采样点数*2
#define GET_UNIT(x) ((x >> 3) & 0x1)

#if CONFIG_IDF_TARGET_ESP32
#define ADC_RESULT_BYTE 2
#define ADC_CONV_LIMIT_EN 1                  // For ESP32, this should always be set to 1
#define ADC_CONV_MODE ADC_CONV_SINGLE_UNIT_1 // ESP32 only supports ADC1 DMA mode
#define ADC_OUTPUT_TYPE ADC_DIGI_OUTPUT_FORMAT_TYPE1
#endif

#if CONFIG_IDF_TARGET_ESP32
static uint16_t adc1_chan_mask = BIT(7);
static uint16_t adc2_chan_mask = 0;
static adc_channel_t channel[1] = {ADC1_CHANNEL_7}; //设置ADC引脚
#endif

static uint32_t ret_num = 0;
static uint8_t result[TIMES] = {0}; //采样结果存放数组
static uint16_t value[2000] = {0};

static const char *TAG = "{adc}";
int countNum;

void countTask(void *param)
{

    while (1)
    {

        vTaskDelay(1000 / portTICK_PERIOD_MS);
        printf("{count}%d\n", countNum);
        // printf("{value}%d\n",p->type1.data);
        countNum = 0;
    }
}

static void continuous_adc_init(uint16_t adc1_chan_mask, uint16_t adc2_chan_mask, adc_channel_t *channel, uint8_t channel_num)
{
    adc_digi_init_config_t adc_dma_config = {
        .max_store_buf_size = 4096,//最大采样缓存
        .conv_num_each_intr = TIMES,
        .adc1_chan_mask = adc1_chan_mask,
        .adc2_chan_mask = adc2_chan_mask,
    };
    ESP_ERROR_CHECK(adc_digi_initialize(&adc_dma_config));

    adc_digi_configuration_t dig_cfg = {
        .conv_limit_en = ADC_CONV_LIMIT_EN,
        .conv_limit_num = 250,
        .sample_freq_hz = 100000, //采样率
        .conv_mode = ADC_CONV_MODE,
        .format = ADC_OUTPUT_TYPE,
    };

    adc_digi_pattern_config_t adc_pattern[SOC_ADC_PATT_LEN_MAX] = {0};
    dig_cfg.pattern_num = channel_num;
    for (int i = 0; i < channel_num; i++)
    {
        uint8_t unit = GET_UNIT(channel[i]);
        uint8_t ch = channel[i] & 0x7;
        adc_pattern[i].atten = ADC_ATTEN_DB_11; //衰减倍率
        adc_pattern[i].channel = ch;
        adc_pattern[i].unit = unit;
        adc_pattern[i].bit_width = SOC_ADC_DIGI_MAX_BITWIDTH; //采样位数

        // ESP_LOGI(TAG, "adc_pattern[%d].atten is :%x", i, adc_pattern[i].atten);
        //  ESP_LOGI(TAG, "adc_pattern[%d].channel is :%x", i, adc_pattern[i].channel);
        // ESP_LOGI(TAG, "adc_pattern[%d].unit is :%x", i, adc_pattern[i].unit);
    }
    dig_cfg.adc_pattern = adc_pattern;
    ESP_ERROR_CHECK(adc_digi_controller_configure(&dig_cfg));
}

#if !CONFIG_IDF_TARGET_ESP32
static bool check_valid_data(const adc_digi_output_data_t *data)
{
    const unsigned int unit = data->type2.unit;
    if (unit > 2)
        return false;
    if (data->type2.channel >= SOC_ADC_CHANNEL_NUM(unit))
        return false;

    return true;
}
#endif

void app_main(void)
{
    xTaskCreate(countTask, "countTask", 1024 * 10, NULL, 2, NULL); //创建任务

    memset(result, 0xcc, TIMES);

    continuous_adc_init(adc1_chan_mask, adc2_chan_mask, channel, sizeof(channel) / sizeof(adc_channel_t));
    adc_digi_start();

    
  
        adc_digi_read_bytes(result, TIMES, &ret_num, ADC_MAX_DELAY);
        for (int i = 0; i < ret_num; i += ADC_RESULT_BYTE)
        {
            adc_digi_output_data_t *p = (void *)&result[i];
            value[i] = p->type1.data;

            // ESP_LOGI(TAG, "%d", p->type1.data);
            // printf("{value}%d\n", p->type1.data);
            countNum++;
            // vTaskDelay(10/ portTICK_PERIOD_MS);
        }
        for (int i = 0; i < ret_num; i += ADC_RESULT_BYTE)
        {
            printf("{value}%d\n", value[i]);
        }
    
}

五、实验验证

首先将采样率配置为1000000hz，即sample_freq_hz = 100000，将esp32与信号发生器连接，信号发生器设置频率为1kHz，一次采样点数为1000，按下复位键开始一次采样1000个点，存入数组中，接着将数组中的值输出至串口绘图软件观察

可见esp32采样到了10个波形，这说明adc的采样率已经配置为了100000hz

六、可能出现的问题

（1）不能将串口输出与ADC采集放在同一个循环中，否则ADC采样率会被串口发送程序拉低，必须独立开。
（2）对于ESP32来说，最好先关闭看门狗，防止ADC读取数据时重启。
（3）数组建立时前面必须加上static，否则单片机内存会爆炸。
（4）rtc控制器与dig控制器最大的区别在于采样率，dig可以配合DMA达到非常高的采样率，但是无法将采样率配置的很低，rtc控制器则相反，可以根据需要使用不同的控制器。
（5）如果将sample_freq_hz = 200000，会发现countNum并不是200000，这是正常现象，因为freertos的多任务系统会降低采样率，但得益于ESP32的240MHz主频，影响一般不大。
（6）ADC2无法和WiFi同时使用。