Embedded software architecture Division

1、 Module partition

（1） It's modular “ draw ” It means planning , It means how to reasonably divide a large software into a series of functionally independent parts , Cooperate to complete the requirements of the system .

（2）C Language as a structured programming language , The division of modules is mainly based on functions .

2、 Method of module division

（1） A module is a .C file , Or a .h Joining of documents , The header file （.h） Is the declaration of the module interface .

（2） The external functions and data provided by a module to other modules need to be called in .h The document is preceded by extern Keyword declaration .

（3） Functions and local variables used only inside the module need to be in .C The document is preceded by static Statement .

（4） Never be in .h Variables defined in file ： The difference between defining variables and declaring variables is that defining variables will produce memory allocation operations .

        stay .h The variable... Is defined in the file , other .C The file refers to the header file , Will make each .C The file defaults this variable to a local variable , This makes this variable unable to play the role of global sharing .

A bad example ：

/*module1.h*/
int a = 5 ; // In the module 1 The file of .h It's defined in the file int a

/*module1.c*/
#include "module1.h" // In the module 1 The file of .c The file contains modules 1 Of .h file 

/*module2.c*/
#include "module1.h" // In the module 2 The file of .c The file contains modules 1 Of .h file 

/*module3.c*/
#include "module1.h" // In the module 3 The file of .c The file contains modules 1 Of .h file 

  A good example ：

/*module1.h*/
extern int a; // In the module 1 The file of .h The document only states int a

/*module1.c*/
#include "module1.h" // In the module 1 The file of .c The file contains modules 1 Of .h file 
int a = 5;   // In the module 1 The file of .c It's defined in the file int a

/*module2.c*/
#include "module1.h" // In the module 2 The file of .c The file contains modules 1 Of .h file 

/*module3.c*/
#include "module1.h" // In the module 3 The file of .c The file contains modules 1 Of .h file 

3、 The type of module

（1） Hardware driver module ： A specific hardware corresponds to a module

（2） Software function module ： The division of its modules should meet the requirements of low coupling 、 High cohesion requirements , A function corresponds to a module .

4、 Task mode ：

（1） A single task ： Micro serial 、 Macro serial

（2） multitasking ： Micro serial 、 Macro parallel

Serial ： Only one task runs at a time .

parallel ： You run multiple tasks in one time period .

5、 Typical single task architecture

（1） from CPU Start execution at the specified address during reset

（2） Jump to assembly code startup Start execution 、 Partial initialization .

（3） Jump to the user main program main To execute , stay main Done in the function ：

        ① Initialize some hardware devices

        ② Initialize each software module

        ③ Into the dead cycle （ Infinite loop ）, Call the processing function of each module .

        The programming method of dead cycle ：

while(1)
{
    //null
}

Or written ：

for(;;)
{    
    //null
}

6、 Interrupt service routine

（1） Interrupt is an important part of embedded system , But in standard C The language does not contain interrupts , Many compiler developers are working on Standards C Added support for interrupts , Provide a new keyword to identify the interrupt service program （ISR）,

for example ：_ _interrupt

（2） When a function is defined as an interrupt function （ISR） When , The compiler will automatically add the interrupt field stack and stack code required by the interrupt service program for this function .

7、 Characteristics of interrupt service program ：

The interrupt service program needs to meet the following requirements ：

（1） Cannot return value

（2） Cannot interrupt function （ISR） Pass parameters

（3）ISR The program should be as short and concise as possible ; Otherwise, the performance of the program will be affected

（4）printf(char *IpFormatString, ...) Functions cause performance problems , Can't be in ISR Use in a function , Because the execution time of variable parameter functions is relatively long .

8、 Interrupt service program model

        In project development , Design a queue , In the interrupt service program , Just add the interrupt type to the queue , Constantly scan the interrupt queue for interrupts in the infinite loop of the main program , If yes, take out the first interrupt type in the queue , Deal with it accordingly .

typedef struct tagIntQueue    // Queue for storing interrupts 
{
    int intType;    // Interrupt type 
    struct tagIntQueue    *next;    // Queue pointer 
}    IntQueue;

IntQueue* IpIntQueueHead;

_ _interrupt ISRexample()
{
    int intType;    // Interrupt type 
    intType = GetSystemType();    // Get interrupt type 
    QueueAddTail(IpIntQueueHead, intType),    // Add a new interrupt to the end of the queue 
}

9、 Main program model

while(1)
{
    if(!IsIntQueueEmpty())
    {
        intType = GetFirstInt();

        switch(intType)
        {
            
            case xxx:    // Interrupt handling function 
                ....
                break;
            case xxx:
                ....
                break;

        }
    }
}