text: // Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //     http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  #include "sdkconfig.h"
  
  #include <string.h>
  #include "bootloader_config.h"
  #include "bootloader_init.h"
  #include "bootloader_utility.h"
  #include "bootloader_common.h"
  #include "esp_image_format.h"
  #include "esp_log.h"
  
  static const char* TAG = "boot";
  
  static esp_err_t select_image (esp_image_metadata_t *image_data);
  static int selected_boot_partition(const bootloader_state_t *bs);
  
  void call_start_cpu(void)
  {
      // 1. Hardware initialization
      if(bootloader_init() != ESP_OK){
          return;
      }
  
      // 2. Select image to boot
      esp_image_metadata_t image_data;
      if(select_image(&image_data) != ESP_OK){
          return;
      }
  
      // 3. Loading the selected image
      bootloader_utility_load_image(&image_data);
  }
  
  // Selects image to boot
  static esp_err_t select_image (esp_image_metadata_t *image_data)
  {
      // 1. Load partition table
      bootloader_state_t bs;// = { 0 };
      memset(&bs, 0, sizeof(bootloader_state_t));
      if (!bootloader_utility_load_partition_table(&bs)) {
          ESP_LOGE(TAG, "load partition table error!");
          return ESP_FAIL;
      }
  
      // 2. Select boot partition
      int boot_index = selected_boot_partition(&bs);
      if(boot_index == INVALID_INDEX) {
          return ESP_FAIL; // Unrecoverable failure (not due to corrupt ota data or bad partition contents)
      }
  
      // 3. Load the app image for booting
      if (!bootloader_utility_load_boot_image(&bs, boot_index, image_data)) {
          return ESP_FAIL;
      }
      return ESP_OK;
  }
  
  /*
   * Selects a boot partition.
   * The conditions for switching to another firmware are checked.
   */
  static int selected_boot_partition(const bootloader_state_t *bs)
  {
      int boot_index = bootloader_utility_get_selected_boot_partition(bs);
      if (boot_index == INVALID_INDEX) {
          return boot_index; // Unrecoverable failure (not due to corrupt ota data or bad partition contents)
      } else {
          // Factory firmware.
  #ifdef CONFIG_BOOTLOADER_FACTORY_RESET
          if (bootloader_common_check_long_hold_gpio(CONFIG_BOOTLOADER_NUM_PIN_FACTORY_RESET, CONFIG_BOOTLOADER_HOLD_TIME_GPIO) == 1) {
              ESP_LOGI(TAG, "Detect a condition of the factory reset");
              bool ota_data_erase = false;
  #ifdef CONFIG_BOOTLOADER_OTA_DATA_ERASE
              ota_data_erase = true;
  #endif
              const char *list_erase = CONFIG_BOOTLOADER_DATA_FACTORY_RESET;
              ESP_LOGI(TAG, "Data partitions to erase: %s", list_erase);
              if (bootloader_common_erase_part_type_data(list_erase, ota_data_erase) == false) {
                  ESP_LOGE(TAG, "Not all partitions were erased");
              }
              return bootloader_utility_get_selected_boot_partition(bs);
          }
  #endif
         // TEST firmware.
  #ifdef CONFIG_BOOTLOADER_APP_TEST
          if (bootloader_common_check_long_hold_gpio(CONFIG_BOOTLOADER_NUM_PIN_APP_TEST, CONFIG_BOOTLOADER_HOLD_TIME_GPIO) == 1) {
              ESP_LOGI(TAG, "Detect a boot condition of the test firmware");
  #ifdef CONFIG_BOOTLOADER_APP_TEST_IN_OTA_1
              /* In this case, test bin will locate in ota_1 by default.
                 This is the solution for small Flash. */
              return 1;
  #else
              if (bs->test.offset != 0) {
                  boot_index = TEST_APP_INDEX;
                  return boot_index;
              } else {
                  ESP_LOGE(TAG, "Test firmware is not found in partition table");
                  return INVALID_INDEX;
              }
  #endif
          }
  #endif
          // Customer implementation.
          // if (gpio_pin_1 == true && ...){
          //     boot_index = required_boot_partition;
          // } ...
      }
      return boot_index;
  }
  