12. Tencent cloud IOT device side learning -- NTP function and Implementation

The main purpose of this series is to record the learning notes of Tencent cloud Internet of things device , And on the device side SDK Make a supplementary explanation .

brief introduction

ntp function

ntp The function is simple uplink and downlink topic Matching functions , The device side subscribes to the downlink topic , Send a message to the uplink topic , Trigger the server to send downlink messages , And process according to the downlink message .

As follows: NTP Function as an example , Introduce how to base on iot-hub-device-c-sdk Realize this function .

Module add

stay services/hub/system/ New modules , Need to achieve

• src： Module source code , Provide sdk External interface
• inc： The module uses header files internally , None in this function
• sample： Sample code , Examples of calling interfaces
• test： Unit test case writing
• CMakeLists.txt：cmake Script , Simply set the source code and header file path , Add examples and unit tests （ Later, it can be simplified without modifying the service ）

NTP The function mainly implements two interfaces ：

• IOT_Sys_GetTime： This interface is used to get the time from the server , Mainly do the following three things
  • _system_mqtt_result_topic_check_and_sub： Detect downlink topic Subscription status , If you don't subscribe, subscribe
  • _system_mqtt_get_resource_time_publish： Up topic Release the news , To get time
  • _system_mqtt_result_wait： Timeout waiting for server reply
• IOT_Sys_SyncNTPTime： and IOT_Sys_GetTime similar , The difference is that it passes according to the time before and after receiving the message HAL_Timer_SetSystimeSec and HAL_Timer_SetSystimeMs Set system time .

The source code to achieve （ see system_mqtt.c）, The following is a brief description of the development ideas of such services ：

1. Sync subscription ： Most services need to ensure the success of the subscription , To ensure the success of the subscription , You can call IOT_MQTT_SubscribeSync
2. Message processing ： The old version of the service will be in mqtt client Add a new member to the structure , Obviously, this is not conducive to code maintenance and subsequent function development , So you can subscribe to the usr_data To pass in the context that needs to be processed by the service , At the same time, we need to usr_data Register the release function of , Because this part follows mqtt client Life cycle exists , When mqtt client Be destroyed when the , It needs to be released usr_data.
3. Interface encapsulation ： Different services require different logic perceived by users , Services identified for such agreements , Generally by SDK encapsulate , Only provide data that users need to be aware of , Such as time .

Add... To the external header file

stay include/services/common Add external header file in qcloud_iot_system.h, It mainly provides external interfaces

Compile add

stay config/settings/iot_hub_setting.cmake Add module compilation in , Simply add the corresponding directory to the compilation , It will automatically detect the CMakeLists.txt

add_subdirectory(${PROJECT_SOURCE_DIR}/services/common/system)