In the process of writing this 8*8 button program, whether in the process of writing or referring to other people's programs, I found that I have a lot of basic knowledge points and programming specifications for C language, and some of them are my previous programming habits. Not good, some are the performance of the basic knowledge is not solid, so summed up.
First, the relationship between .H files and .C files:
So far, the programs I have written are very simple programs. I never thought of writing .H files myself. I don't know what the .H files are for, and what is related to .C files. Just recently wrote the keyboard program, refer to other people's programs, found that the strict procedures written by others have a "KEY.H", which defines the functions written in the .C file, such as Keyhit (), Keyscan ()Wait.
After looking up the information, the .H file is the header file, which is estimated to be the meaning of the Head. This is the need to standardize the program's structured design. It can realize the modularization of large programs and the connection debugging of the root modules.
1. Introduction to .H file:
In the design of the MCU C program, the project is generally structured and structured according to functional modularity. A project is divided into multiple functions, and the related program of each function is placed in a C program document, which is called a module, and the corresponding file name is the module name. A module usually consists of two documents, one for the header file *.h, which describes the data structure and function prototype in the module; the other is the C file *.c, the definition of the data instance or object, and the function algorithm specific achieve.
2. The role of the .H file
As a project design, in addition to a detailed description of the overall function of the project, each module is defined in detail, that is, the header files of all modules are given. Usually the H header file defines the function of each function in the module, as well as the requirements of the input and output parameters. The specific implementation of the module is completed by the project design, programming and debugging according to the H file. For confidentiality and security, the module is implemented and provided to other members of the project in the form of a connectable file OBJ or a library file LIB. Since the source program documentation is not provided, it can be publicly released on the one hand to ensure the ownership of the developer; on the other hand, it can prevent others from intentionally or unintentionally modifying the non-conformity, resulting in version confusion. Therefore, the H header file is the basis for the detailed design of the project and the division of the team work, and is also a functional description of the module test. To reference the data or algorithm in the module, just use the include include module H header file.
3. The basic composition of the .H file
/*The following is the keyboard driver's header document*/
#ifndef _KEY_H_ //Anti-duplicate reference, if _KEY_H_ is not defined, compile the following sentence
#define _KEY_H_ //This symbol is unique, indicating that the symbol _KEY_H_ is defined as long as it is referenced once, ie #i nclude
//////////////////////////////////////////////////////////// ///////////////
Char keyhit( void ); //click key
Unsigned char Keyscan( void ); //take the key value
//////////////////////////////////////////////////////////// ///////////////
#endif
Second, try to use macro definition #define
When I started looking at other people's programs, I found that at the beginning of the program, there were a lot of #define statements after the file was included. At that time, I thought that it would not be a hassle to replace so many identifiers. I didn't understand the benefits of this writing. Originally, using a identifier to indicate a constant is conducive to future modification and maintenance. When you modify it, you only need to change it at the beginning of the program. All the places used in the program are modified to save time.
#define KEYNUM 65//Number of buttons for Keycode[KEYNUM]
#define LINENUM 8//Keyboard lines
#define ROWNUM 8//Keyboard Columns
Note:
1, the macro name is generally capitalized
2, the macro definition is not a C statement, no semicolon at the end
Third, do not arbitrarily define variable types
When writing a program before, when a new variable is needed, whether it is outside the function or outside the function, it is defined directly at the beginning of the program. Although it is not a principle error, it is not advisable.
Let's talk about the related concepts of variable types in C:
From the scope of the variable, it is divided into local variables and global variables:
1, global variables: is a variable defined outside the function, like the variables I defined at the beginning of the program are global variables, here I made a big taboo, using too many global variables.
There are two problems: First, the global variables occupy resources in the entire execution process of the program; second, too many global variables make the program's versatility worse, because global variables are one of the reasons for coupling between modules.
2, local variables: variables defined inside the function, only valid inside the function.
There are two types of time from the variable value of the variable:
1. Static storage variables: A fixed storage space is allocated during program running.
2. Dynamic storage variables: The storage space is dynamically allocated as needed during program execution.
Specifically, it includes four storage methods: auto static register extern
1, local variables, without explanation, the default is auto type, that is, dynamic storage, if you do not assign an initial value, it will be an indeterminate value. When a local variable is defined as a static type, its value is constant within the function, and the initial value defaults to 0.
Static unsigned char sts;//button state variable
Static unsigned char Nowkeycode; / / key code at this time
Static unsigned char Prekeycode;//last key code
Static unsigned char Keydowntime;//Rectangle keyboard press debounce time variable
Static unsigned char Keyuptime;//Rectangle keyboard release debounce time variable
Static unsigned char Onoffdowntime; / / shutdown button press debounce time variable
Static unsigned char Onoffuptime; / / shutdown button release debounce time variable
Static unsigned char onoff_10ms; / / determine the shutdown key interrupt number variable, the cumulative 150 times is about 3S, because the two into the 10ms interrupt
2, global variables, allocated as static storage at compile time, can be referenced by each function in this file. If there are multiple files, if you refer to variables in another file in one file, use extern in this file. However, if a global variable is defined as static, it can only be used in this file.
Fourth, the use of special keywords const volatile
1, const
Const is used to declare a read-only variable
Const unsigned char a=1; / / define a = 1, the compiler is not allowed to modify the value of a
Role: to protect parameters that do not want to be modified
Const unsigned char Key_code[KEYNUM]={0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,
0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10,
0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18,
0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x20,
0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,
0x29, 0x2A, 0x2B, 0x2C, 0x2D, ​​0x2E, 0x2F, 0x30,
0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38,
0x39, 0x3A, 0x3B, 0x3C, 0x3D, 0x3E, 0x3F, 0x40,
0x41
};//Key code
Const unsigned char Line_out[LINENUM]={0xFE,0xFD,0xFB,0xf7,0xEF,0xDF,0xBF,0x7F};//row output coding
Const unsigned char Row_in[ROWNUM]={0xFE,0xFD,0xFB,0xf7,0xEF,0xDF,0xBF,0x7F};//column input encoding
2, volatile
A variable defined as volatile means that the variable may be unexpectedly changed so that the compiler does not assume the value of the variable. To be precise, the optimizer must carefully re-read the value of this variable each time it uses this variable instead of using the backup stored in the register.
Static int i=0;
Int main(void)
{
...
While (1)
{
If (i)
Dosomething();
}
}
/* Interrupt service routine. */
Void ISR_2(void)
{
i=1;
}
The original intention of the program is to call the dosomething function in main when the ISR_2 interrupt is generated. However, since the compiler has not modified i in the main function, it may only perform a read operation from i to a register, and then each time. The if statement uses only the "i copy" in this register, causing the dosomething to never be called. If the variable is added with a volatile modifier, the compiler guarantees that the read and write operations on this variable will not be optimized (sincere execution).
In general, volatile is used in the following places:
1. The variable modified by the interrupt service program for other programs needs to be added with volatile;
2. The flags shared between tasks in a multi-tasking environment should be volatile;
3, the memory mapped hardware registers usually also have to be volatile, because each time it is read and written by the different meaning;
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