feature(adc): add adc example

examples/peripherals/adc/main/adc_example_main.c

@@ -0,0 +1,55 @@
+/* adc example
+
+   This example code is in the Public Domain (or CC0 licensed, at your option.)
+
+   Unless required by applicable law or agreed to in writing, this
+   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+   CONDITIONS OF ANY KIND, either express or implied.
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+#include "driver/adc.h"
+#include "esp_log.h"
+
+static const char *TAG = "adc example";
+
+static void adc_task()
+{
+    int x;
+    uint16_t adc_data[100];
+
+    while (1) {
+        if (ESP_OK == adc_read(&adc_data[0])) {
+            ESP_LOGI(TAG, "adc read: %d\r\n", adc_data[0]);
+        }
+
+        ESP_LOGI(TAG, "adc read fast:\r\n");
+
+        if (ESP_OK == adc_read_fast(adc_data, 100)) {
+            for (x = 0; x < 100; x++) {
+                printf("%d\n", adc_data[x]);
+            }
+        }
+
+        vTaskDelay(1000 / portTICK_RATE_MS);
+    }
+}
+
+void app_main()
+{
+    // 1. init adc
+    adc_config_t adc_config;
+
+    // Depend on menuconfig->Component config->PHY->vdd33_const value
+    // When measuring system voltage(ADC_READ_VDD_MODE), vdd33_const must be set to 255.
+    adc_config.mode = ADC_READ_TOUT_MODE;
+    adc_config.clk_div = 8; // ADC sample collection clock = 80MHz/clk_div = 10MHz
+    ESP_ERROR_CHECK(adc_init(&adc_config));
+
+    // 2. Create a adc task to read adc value
+    xTaskCreate(adc_task, "adc_task", 1024, NULL, 5, NULL);
+}