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Overview

Last updated: 2021-08-23 11:33:41

    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

    No. Function Description
    1 HAL_Malloc Dynamically applies for memory block
    2 HAL_Free Releases memory block
    3 HAL_ThreadCreate Creates thread
    4 HAL_ThreadDestroy Terminates thread
    5 HAL_MutexCreate Creates mutex lock
    6 HAL_MutexDestroy Terminates mutex lock
    7 HAL_MutexLock Locks mutex
    8 HAL_MutexUnlock Unlocks mutex
    9 HAL_SemaphoreCreate Creates semaphore
    10 HAL_SemaphoreDestroy Terminates semaphore
    11 HAL_SemaphoreWait Waits for semaphore
    12 HAL_SemaphorePost Releases semaphore
    13 HAL_SleepMs Sleeps

    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.

    No. Function Description
    1 HAL_TCP_Connect Establishes TCP connection
    2 HAL_TCP_Disconnect Closes TCP connection
    3 HAL_TCP_Write Writes data to TCP connection
    4 HAL_TCP_Read Reads data from TCP connection
    5 HAL_TLS_Connect Establishes TLS connection
    6 HAL_TLS_Disconnect Closes TLS connection
    7 HAL_TLS_Write Writes data to TLS connection
    8 HAL_TLS_Read Reads data from TLS connection
    9 HAL_UDP_Connect Establishes UDP connection
    10 HAL_UDP_Disconnect Closes UDP connection
    11 HAL_UDP_Write Writes data to UDP connection
    12 HAL_UDP_Read Reads data from UDP connection
    13 HAL_DTLS_Connect Establishes DTLS connection
    14 HAL_DTLS_Disconnect Closes DTLS connection
    15 HAL_DTLS_Write Writes data to DTLS connection
    16 HAL_DTLS_Read Reads data from DTLS connection

    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.

    No. Function Description
    1 HAL_AT_Uart_Init Initializes AT serial port
    2 HAL_AT_Uart_Deinit Deinitializes AT serial port
    3 HAL_AT_Uart_Send Sends data over AT serial port
    4 HAL_AT_UART_IRQHandler Handles AT serial port receipt interruption

    Time and print HAL APIs

    No. Function Description
    1 HAL_Printf Writes formatted data to standard output stream
    2 HAL_Snprintf Writes formatted data to string
    3 HAL_UptimeMs Retrieves the number of milliseconds that elapsed since the system has started
    4 HAL_DelayMs Blocking delay in milliseconds

    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.

    No. Function Description
    1 HAL_GetDevInfo Reads device information
    2 HAL_SetDevInfo Saves device Information
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