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DocumentationIoT HubDevice Connection ManualConnection Based on SDK for CSDK for C Use InstructionsUsage Overview
Usage Overview
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Last updated: 2024-12-27 16:55:24
Usage Overview
Last updated: 2024-12-27 16:55:24
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IoT Hub device SDK for C relies on a secure and powerful data channel to enable IoT developers to quickly connect devices to the cloud for two-way communication.
Note:
After v3.1.0, the SDK refactored and optimized the compilation environment, code, and directory structure, increasing the availability and portability.

Scope of Application of SDK for C

Featuring a modular design, the SDK for C separates the core protocol service from the hardware abstraction layer and provides flexible configuration options and multiple compilation methods, making it suitable for development platforms and use environments of different devices.

Network communication-capable devices on Linux/Windows

For devices that have network communication capabilities and run on standard Linux/Windows, such as PCs, servers, and gateway devices, as well as advanced embedded devices such as Raspberry Pi, you can directly compile and run the SDK on them.
For embedded Linux devices that require cross compilation, if the toolchain of the development environment has glibc or similar libraries which can provide system calls, including socket communication, SELECT sync IO, dynamic memory allocation, functions for getting time/sleeping/generating random number/printing, as well as critical data protection such as the mutex mechanism (only when multiple threads are required), only simple adaptation (e.g., changing the cross compiler settings in CMakeLists.txt or make.settings) is required before the SDK can be compiled and run.

Network communication-capable devices on RTOS

For IoT devices that have network communication capabilities and run on RTOS, the SDK for C needs to be adapted to different RTOS systems for porting. Currently, it has been adapted to multiple IoT-oriented RTOS platforms, including FreeRTOS, RT-Thread, and TencentOS tiny.
When porting the SDK to an RTOS device, if the platform provides C runtime libraries like Newlib and embedded TCP/IP protocol stacks like lwIP, adaptation for porting can be done easily.

Devices with MCU + communication module

For MCUs that have no network communication capabilities, the "MCU + communication module" combination is often used. Communication modules (including Wi-Fi/2G/4G/NB-IoT) generally provide serial port-based AT instruction protocols for MCUs to communicate over the network. For this scenario, the SDK for C encapsulates the AT-socket network layer, where the core protocol and service layer don't need to be ported. In addition, it provides FreeRTOS-based and nonOS HAL implementation methods.
In addition, IoT Hub provides a dedicated AT instruction set. If the communication module implements this instruction set, it will be easier for devices to connect and communicate, and less code will be required. For this scenario, please refer to the SDK for MCU AT dedicated to the Tencent Cloud customized AT module.

SDK Directory Structure Overview

The directory structure and top-level documents are described as follows:
Name
Description
CMakeLists.txt
CMake compilation and description file
CMakeSettings.json
CMake configuration file on Visual Studio
cmake_build.sh
Compilation script with CMake on Linux
make.settings
Configuration file compiled directly by Makefile on Linux
Makefile
Direct compilation with Makefile on Linux
device_info.json
Device information file. If DEBUG_DEV_INFO_USED = OFF, the device information will be parsed from this file
docs
Documentation directory, i.e., the use instructions of the SDKs for different platforms
external_libs
Third-party package components, such as Mbed TLS
samples
Application demos
include
External header files provided to users
platform
Platform source code files. Currently, implementations are provided for different OS (Linux/Windows/FreeRTOS/nonOS), TLS (Mbed TLS), and AT module
sdk_src
Core communication protocols and service code of the SDK
tools
Compilation and code generation script tools supporting the SDK

SDK Compilation Method Description

The SDK for C supports three compilation methods:
CMake
Makefile
Code extraction
For more information on the compilation methods and compilation configuration options, please see Compilation Configuration Description and Compilation Environment (Linux and Windows).

SDK Demos

The samples directory of the SDK for C contains demos showing how to use the features. For more information on how to run the demos, please see the corresponding documents in the SDK documentation directory. For more information on device connection to and message sending/receiving in IoT Hub over MQTT, please see Getting Started with MQTT.

Notes

API changes for OTA update

Starting from SDK v3.0.3, OTA update supports checkpoint restart. When the firmware download process is interrupted due to network exceptions or other issues, the downloaded part of the firmware can be saved, so that the download can start from where interrupted instead of from the beginning when it is resumed. After this new feature was supported, the methods of using relevant OTA APIs changed. If you have upgraded from v3.0.2 or below, you should modify your logic code; otherwise, firmware download will fail. For more information on how to modify it, please see samples/ota/ota_mqtt_sample.c.

Code name changes

To improve the code readability and comply with the naming conventions, SDK v3.1.0 incorporated changes to certain variables, functions, and macro names. If you have upgraded from v3.0.3 or below, you can run the tools/update_from_old_SDK.sh script on Linux to replace the names in your own code, and then you can use the new version of the SDK directly.
Old Name
New Name
QCLOUD_ERR_SUCCESS
QCLOUD_RET_SUCCESS
QCLOUD_ERR_MQTT_RECONNECTED
QCLOUD_RET_MQTT_RECONNECTED
QCLOUD_ERR_MQTT_MANUALLY_DISCONNECTED
QCLOUD_RET_MQTT_MANUALLY_DISCONNECTED
QCLOUD_ERR_MQTT_CONNACK_CONNECTION_ACCEPTED
QCLOUD_RET_MQTT_CONNACK_CONNECTION_ACCEPTED
QCLOUD_ERR_MQTT_ALREADY_CONNECTED
QCLOUD_RET_MQTT_ALREADY_CONNECTED
MAX_SIZE_OF_DEVICE_SERC
MAX_SIZE_OF_DEVICE_SECRET
devCertFileName
dev_cert_file_name
devPrivateKeyFileName
dev_key_file_name
devSerc
device_secret
MAX_SIZE_OF_PRODUCT_KEY
MAX_SIZE_OF_PRODUCT_SECRET
product_key
product_secret
DEBUG
eLOG_DEBUG
INFO
eLOG_INFO
WARN
eLOG_WARN
ERROR
eLOG_ERROR
DISABLE
eLOG_DISABLE
Log_writter
IOT_Log_Gen
qcloud_iot_dyn_reg_dev
IOT_DynReg_Device
IOT_SYSTEM_GET_TIME
IOT_Get_SysTime
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