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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 C-SDK encapsulates the AT-socket network layer, where the core protocol and service layer don't need to be ported. This document describes how to port C-SDK for connection to IoT Hub in the target environment of MCU (nonOS) + universal TCP AT module.
Compared with the RTOS scenario, the network data received by at_socket is processed differently. The application layer needs to periodically call IOT_MQTT_Yield to receive the server's downstream data. If the receipt window is missed, there will be data loss. Therefore, in scenarios with complex business logic, we recommended you use RTOS and select the nonOS mode by configuring FEATURE_AT_OS_USED = OFF.

SDK Download

Download the latest version of the device C-SDK.

SDK Feature Configuration

Use the general TCP module to compile and configure the options for nonOS as follows:

Code Extraction

1. Run the following command on Linux:

   mkdir build
   cd build
   cmake ..
   

2. 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.
   • platform directory: contains platform-related code, which can be modified and adapted according to the specific conditions of the device.
   • 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.

3. 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.

HAL Porting

Please refer to Overview first.

For network HAL APIs, the AT_Socket framework provided by the SDK has been selected through the above compilation options. The SDK will call the at_socket API of network_at_tcp.c. You don't need to port the at_socket layer, but you need to implement the AT serial port driver and AT module driver. For the AT module driver, you only need to implement the driver API of the driver structure at_device_op_t in at_device of the AT framework. You can refer to the supported modules in the at_device directory. For the AT serial port driver, you need to implement serial port receipt interruption and then call the callback function at_client_uart_rx_isr_cb in the interruption service program. You can refer to HAL_OS_nonos.c to port for the target platform.

Business Logic Development

You can refer to the routines in the SDK's samples directory for development.