text: // Copyright 2015-2018 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.
  #pragma once
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  #include "esp_types.h"
  #include "esp_err.h"
  #include "esp_modem_dte.h"
  
  typedef struct modem_dce modem_dce_t;
  typedef struct modem_dte modem_dte_t;
  
  /**
   * @brief Result Code from DCE
   *
   */
  #define MODEM_RESULT_CODE_SUCCESS "OK"              /*!< Acknowledges execution of a command */
  #define MODEM_RESULT_CODE_CONNECT "CONNECT"         /*!< A connection has been established */
  #define MODEM_RESULT_CODE_RING "RING"               /*!< Detect an incoming call signal from network */
  #define MODEM_RESULT_CODE_NO_CARRIER "NO CARRIER"   /*!< Connection termincated or establish a connection failed */
  #define MODEM_RESULT_CODE_ERROR "ERROR"             /*!< Command not recognized, command line maximum length exceeded, parameter value invalid */
  #define MODEM_RESULT_CODE_NO_DIALTONE "NO DIALTONE" /*!< No dial tone detected */
  #define MODEM_RESULT_CODE_BUSY "BUSY"               /*!< Engaged signal detected */
  #define MODEM_RESULT_CODE_NO_ANSWER "NO ANSWER"     /*!< Wait for quiet answer */
  
  /**
   * @brief Specific Length Constraint
   *
   */
  #define MODEM_MAX_NAME_LENGTH (32)     /*!< Max Module Name Length */
  #define MODEM_MAX_OPERATOR_LENGTH (32) /*!< Max Operator Name Length */
  #define MODEM_IMEI_LENGTH (15)         /*!< IMEI Number Length */
  #define MODEM_IMSI_LENGTH (15)         /*!< IMSI Number Length */
  
  /**
   * @brief Specific Timeout Constraint, Unit: millisecond
   *
   */
  #define MODEM_COMMAND_TIMEOUT_DEFAULT (500)      /*!< Default timeout value for most commands */
  #define MODEM_COMMAND_TIMEOUT_OPERATOR (75000)   /*!< Timeout value for getting operator status */
  #define MODEM_COMMAND_TIMEOUT_MODE_CHANGE (3000) /*!< Timeout value for changing working mode */
  #define MODEM_COMMAND_TIMEOUT_HANG_UP (90000)    /*!< Timeout value for hang up */
  #define MODEM_COMMAND_TIMEOUT_POWEROFF (1000)    /*!< Timeout value for power down */
  
  /**
   * @brief Working state of DCE
   *
   */
  typedef enum {
      MODEM_STATE_PROCESSING, /*!< In processing */
      MODEM_STATE_SUCCESS,    /*!< Process successfully */
      MODEM_STATE_FAIL        /*!< Process failed */
  } modem_state_t;
  
  /**
   * @brief DCE(Data Communication Equipment)
   *
   */
  struct modem_dce {
      char imei[MODEM_IMEI_LENGTH + 1];                                                 /*!< IMEI number */
      char imsi[MODEM_IMSI_LENGTH + 1];                                                 /*!< IMSI number */
      char name[MODEM_MAX_NAME_LENGTH];                                                 /*!< Module name */
      char oper[MODEM_MAX_OPERATOR_LENGTH];                                             /*!< Operator name */
      modem_state_t state;                                                              /*!< Modem working state */
      modem_mode_t mode;                                                                /*!< Working mode */
      modem_dte_t *dte;                                                                 /*!< DTE which connect to DCE */
      esp_err_t (*handle_line)(modem_dce_t *dce, const char *line);                     /*!< Handle line strategy */
      esp_err_t (*sync)(modem_dce_t *dce);                                              /*!< Synchronization */
      esp_err_t (*echo_mode)(modem_dce_t *dce, bool on);                                /*!< Echo command on or off */
      esp_err_t (*store_profile)(modem_dce_t *dce);                                     /*!< Store user settings */
      esp_err_t (*set_flow_ctrl)(modem_dce_t *dce, modem_flow_ctrl_t flow_ctrl);        /*!< Flow control on or off */
      esp_err_t (*get_signal_quality)(modem_dce_t *dce, uint32_t *rssi, uint32_t *ber); /*!< Get signal quality */
      esp_err_t (*get_battery_status)(modem_dce_t *dce, uint32_t *bcs,
                                      uint32_t *bcl, uint32_t *voltage);  /*!< Get battery status */
      esp_err_t (*define_pdp_context)(modem_dce_t *dce, uint32_t cid,
                                      const char *type, const char *apn); /*!< Set PDP Contex */
      esp_err_t (*set_working_mode)(modem_dce_t *dce, modem_mode_t mode); /*!< Set working mode */
      esp_err_t (*hang_up)(modem_dce_t *dce);                             /*!< Hang up */
      esp_err_t (*power_up)();                                            /*!< Normal power up */
      esp_err_t (*open)(modem_dce_t *dce);                                /*!< Opening device */
      esp_err_t (*power_down)(modem_dce_t *dce);                          /*!< Normal power down */
      esp_err_t (*deinit)(modem_dce_t *dce);                              /*!< Deinitialize */
  };
  
  #ifdef __cplusplus
  }
  #endif
  