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This document describes how to port the device C-SDK to the target hardware platform. C-SDK adopts modular design to separate the core protocol service and hardware abstraction layer (HAL). When porting across platforms, you generally only need to modify and adapt the HAL.

C-SDK Architecture

Architecture diagram

Architecture description

The SDK is designed into four layers from top to bottom: platform service layer, core protocol layer, network layer, and hardware abstraction layer.

• Service layer
  This layer is above the network protocol layer and implements features such as device connection authentication, device shadow, gateway, dynamic registration, log reporting, and OTA.
• Protocol layer
  The network protocols over which devices can interact with the IoT Hub platform include MQTT, CoAP, and HTTP.
• Network layer
  This layer implements network protocol stacks based on TLS/SSL (TLS/DTLS), POSIX_socket (TCP/UDP), and AT_socket. Different services can use different protocol stack API functions as needed.
• Hardware abstraction layer
  To implement the abstract encapsulation of underlying operations of different hardware platforms, it is necessary to conduct porting for the specific software and hardware platforms, which is divided into two parts of required and optional HAL APIs.

HAL Porting

HAL mainly has several major parts for porting, including those related to the OS, network and TLS, time and print, and device information.
In the platform/os directory, the SDK demonstrates the implementation of HAL in four scenarios: Linux, Windows, FreeRTOS, and nonOS. You can refer to the corresponding directory to port for the target platform.

OS APIs

Network and TLS HAL APIs

Network APIs provide either-or adaptation and porting. For devices that have network communication capabilities and integrate TCP/IP network protocol stacks, you need to implement the POSIX_socket network HAL APIs. For devices using TLS/SSL for encrypted communication, you also need to implement the TLS HAL APIs. For devices with MCU + universal TCP_AT module, you can choose the AT_Socket framework provided by the SDK and implement relevant AT module APIs.

HAL APIs based on POSIX_socket

Among them, TCP/UDP APIs are implemented based on POSIX socket functions. TLS APIs are dependent on the mbedtls library. Before porting, you must ensure that the mbedtls library is available on the system. If you use other TLS/SSL libraries, please refer to the relevant implementation of platform/tls/mbedtls for porting and adapting.
UDP/DTLS functions need to be ported only when CoAP communication is enabled.

HAL APIs based on AT_socket
After AT_socket is selected by enabling the compilation macro AT_TCP_ENABLED, 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_AT_UART_freertos.c to port for the target platform.

Time and print HAL APIs

Device information HAL APIs

To connect a device to the IoT Hub platform, you need to create product and device information on the platform and save such information in a non-volatile storage medium on the device. You can refer to platform/os/linux/HAL_Device_linux.c for implementation.