I believe that many engineers will often see the macro definition shown below, according to the macro definition, and these macro definitions seem to have some initialization functions. Some statements. .
As shown in the figure above, through the trace discovery of the source code, these init_xxx_export's macro definition is ultimately calling the init_export macro definition, and this macro definition is to put the initialization function in the custom RTI_FN symbol section, the source code is The RTDef.h header file is shown below.
Place the initialization function in a custom symbol section, what effect? The answer is that in this way, these initialization functions can be implicitly called without manually adding the function to the initialization of RT-Thread.
What is implicit call? Implicit call means that when we add a system component or external device to the project code, this component or device needs to perform initialization, and this initialization function, we don't need to start the main function or RT-Thread. Directly add calls in the function, which avoids the modification of the startup process code of RT-Thread.
Let's take a look at the RT-Thread's launch function call process, pay attention to the contents of the red box, as shown below.
Inside the start function, RT_Components_Board_init () and RT_Components_init () These two functions are specifically used to process the prototypes and comments of automatic initialization, the two functions, as shown below.
As can be seen from the above function prototype, these two functions are from the symbol segment interval, which continues to traverse the initialization function in the symbol segment via the for loop, and get the pointer to these initialization functions, and then call to achieve the device or The purpose of the components initialization.
The RT_Components_Board_init () function is executed first, this function is used to initialize the hardware related to the chip, which traverses the list of functions declared with the init_board_export (fn).
The RT_Components_Init () function is that after the system is started, this function is used in the MAIN thread, which is used to initialize other functions lists with init_xxx_export (fn) declaration.
At present, the RT-THREAD core is used to implement the macro definition interface of the automatic initialization function, as shown in the following figure.
In summary, the automatic initialization process to be used in RT-THREAD can be summarized as follows.
Why can I be automatically called after the initialization function adds a symbolic segment? What is the symbol section? What is the benefit of using this way?
Add a function to the symbol section, in fact, using the __attribute __((X))) keyword using the MDK compiler, declares the function, and the function declared through the section keyword, when the compiler is linked, These functions will be collected automatically and put them in a centralized area to view the following. Map files can be seen.
As shown in the red box above, RT_HW_PIN_INIT and RT_HW_USART_INIT are functions that use the init_board_export (fn) declared, so they are stored in the interval in which the orange vertical line is located, using the rt_components_board_init () function to traverse this range.
As shown in the blue box and green box above, they are functions that use init_component_export (fn) and init_app_export (fn), which are stored in the range where red vertical line is located, using the rt_components_init () function to this interval Traverse.
From the above analysis, it can be seen that the way the initialization function is stored in the way, the advantage is that when I need to add a new initialization function, I don't need to change the startup code of RT-Thread, directly through the section keyword. , Add the initialization function to the corresponding symbol section.
The above is the automatic initial mechanism analysis of RT-Thread, is because of this mechanism, so when we cut the kernel or component, it is not necessary to modify the initialization function of RT-Thread, or initialize the components. .
Editor: lq, Read full text, original text title: [RT-THREAD topic 3] RT-THREAD startup process analysis RT-THREAD automatic initialization mechanism analysis
Article Source: [Micro Signal: RTTHREAD, WeChat public number: Lilda Terrain] Welcome to add attention! Please indicate the source of the article.
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