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This document describes how to port IoT Hub C-SDK to the FreeRTOS + lwIP platform.

FreeRTOS Porting Overview

As a micro-kernel system, FreeRTOS mainly provides core OS mechanisms such as task creation and scheduling and inter-task communication. Different device platforms also should be equipped with different software components before they can form a complete embedded operating platform, including C runtime libraries (such as Newlib or ARM CMSIS library) and TCP/IP network protocol stacks (such as lwIP). In addition, the compilation and development environments vary by device platform, so when porting C-SDK, you need to adapt it according to the specific conditions of different devices.

Note：

The SDK provides a reference implementation based on FreeRTOS + lwIP + Newlib in platform/os/freertos, which has been verified and tested on Espressif's ESP8266 platform.

Code Extraction

Because different RTOS-based platforms have different compilation methods, it is generally impossible to directly use the SDK's CMake or Make to compile. Therefore, the SDK provides the code extraction feature. It allows you to extract the relevant code into a separate folder based on your needs. The code hierarchy in the folder is concise, making it easy for you to copy and integrate it into your own development environment.

1. Change the platform in CMakeLists.txt to FreeRTOS and enable the code extraction feature:

   set(BUILD_TYPE                  "release")
   set(PLATFORM                     "freertos")
   set(EXTRACT_SRC ON)
   set(FEATURE_AT_TCP_ENABLED OFF)
   

2. Run the following command on Linux:

   mkdir build
   cd build
   cmake ..
   

3. You can find the relevant code files in output/qcloud_iot_c_sdk with the following directory hierarchy:

    qcloud_iot_c_sdk
   ├── include
   │   ├── config.h
   │   ├── exports
   ├── platform
   └── sdk_src
     └── internal_inc
   

Note：

• include directory: contains the SDK APIs and variable parameters, where config.h is the compilation macros generated according to the compilation options. For more information, please see API and Variable Parameter Description.
• platform directory: contains platform-related code, which can be modified and adapted according to the specific conditions of the device. For more information on functions, please see Overview.
• sdk_src directory: contains the SDK core logic and protocol-related code, which generally don't need to be modified, where internal_inc is the header file used internally by the SDK.

4. You can copy qcloud_iot_c_sdk to the compilation and development environment of your target platform and then modify the compilation options as needed.

Porting Sample

Build a demo project based on Espressif's ESP8266 RTOS platform in the Linux development environment.

1. Please refer to ESP8266_RTOS_SDK to obtain the RTOS_SDK and cross compiler and create a project.
2. Copy the qcloud_iot_c_sdk directory extracted above to components/qcloud_iot.
3. In components/qcloud_iot, create a compilation configuration file component.mk with the following content:

   #
   # Component Makefile
   #
   COMPONENT_ADD_INCLUDEDIRS := \
   qcloud_iot_c_sdk/include \
   qcloud_iot_c_sdk/include/exports \
   qcloud_iot_c_sdk/sdk_src/internal_inc
   COMPONENT_SRCDIRS := \
   qcloud_iot_c_sdk/sdk_src \
   qcloud_iot_c_sdk/platform
   

At this point, you can compile qcloud_iot_c_sdk as a component and then call the IoT Hub C-SDK APIs in your code to connect devices and send/receive messages.