frame.c

一个将数据打包成以太网帧的示例程序

#include "stdio.h" 
#include "conio.h" 
#include "stdlib.h" 
#include "io.h" 
#include "fcntl.h" 
#include "string.h" 
#include "alloc.h" 
#define BUFFER_MAX 1500 
#define BUFFER_MIN 46 
#define PREAMBLE_LEN 8 
#define DEST_LEN 6 
#define SOURCE_LEN 6 
#define FLIE_LENGTH_LEN 2 
#define FCS_LEN 4 
char preamble[8]={0x55,0x55,0x55,0x55,0x55,0x55,0x55,0xD5};/* 前导码 */ 
char addr_dest[6]={0x0,0x0,0x0,0x0,0x0,0x0}; 
char addr_source[6]={0x0,0x0,0x0,0x0,0x0,0x0}; 
long *fcs; 
char *fill_data; 
char *infilename[10]; 
char *outfilename[10]; 
void fill(int x); /*填充函数 */ 
void framer(); 
void init_crc32_table(); 
void GenerateCRC32(char* DataBuf,unsigned long len); 
unsigned long crc32_table[256]; 
unsigned long ulPolynomial = 0x04c11db7; 
void main(int argc,char *argv[]) /* 主函数 */ 
{ 
	clrscr(); 
	if(argc<3) 
	{ 
		printf("command number error!"); 

	} 

	stpcpy(infilename,argv[1]); 
	stpcpy(outfilename,argv[2]);
	
	init_crc32_table(); 

	framer(); 

	printf("framer success!"); 

	getch(); 
} 


void framer() /* 封装函数 */ 
{ 
	char *buff_p; 
	unsigned int buff_length; 
	int read_handle,write_handle; /* 声明文件句柄 */ 
	long file_back,file_length; 
	long file_offset; 
	int conditional=1; 
	int * c; 

	if((read_handle=open(infilename,O_BINARY|O_RDONLY))<0) /* 以只读方式打开文件，并返回句柄 */ 
		printf("open input file error!"); 

	if((write_handle=open(outfilename,O_BINARY|O_WRONLY|O_CREAT))<0) /* 以只写方式打开文件，并返回句柄 */ 
		printf("open output file error!"); 

	file_length=filelength(read_handle); /*文件长度*/ 
	file_back=file_length; /*file_back是文件剩余读取长度*/ 

	while(conditional) /* 循环取数据，直到文件尾 */ 
	{ 

		file_offset=file_length-file_back; /*文件当前位置*/ 
		file_offset=lseek(read_handle,file_offset,SEEK_SET); 

		if(file_back>BUFFER_MAX) 
		{ 
			buff_length=PREAMBLE_LEN+DEST_LEN+SOURCE_LEN+FLIE_LENGTH_LEN+BUFFER_MAX+FCS_LEN; /*定义缓冲区长度*/ 

			buff_p=(char *) malloc(buff_length); 
			
			memcpy(buff_p,preamble,PREAMBLE_LEN); /* 缓冲区加入前导码和界定符 */ 
			memcpy(buff_p+PREAMBLE_LEN,addr_dest,DEST_LEN); /* 加入目的地址 */ 
			memcpy(buff_p+PREAMBLE_LEN+DEST_LEN,addr_source,SOURCE_LEN); /* 加入源地址 */ 

			*c=BUFFER_MAX&0xFFFF; 

			memcpy(buff_p+PREAMBLE_LEN+DEST_LEN+SOURCE_LEN,c,FLIE_LENGTH_LEN); /* 加入长度字段 */ 

			read(read_handle,buff_p+PREAMBLE_LEN+DEST_LEN+SOURCE_LEN+FLIE_LENGTH_LEN,BUFFER_MAX); /* 加入数据 */ 

			GenerateCRC32(buff_p+PREAMBLE_LEN,DEST_LEN+SOURCE_LEN+FLIE_LENGTH_LEN+BUFFER_MAX); 

			memcpy(buff_p+PREAMBLE_LEN+DEST_LEN+SOURCE_LEN+FLIE_LENGTH_LEN+BUFFER_MAX,fcs,FCS_LEN); /* 加入效验码 */ 

			write(write_handle,buff_p,buff_length); 

			file_back=file_back-BUFFER_MAX; 

			conditional=1; 

		} 
		else if(file_back<BUFFER_MIN) 
		{ 

			buff_length=PREAMBLE_LEN+DEST_LEN+SOURCE_LEN+FLIE_LENGTH_LEN+BUFFER_MIN+FCS_LEN; 
			buff_p=(char *) malloc(buff_length); 

			memcpy(buff_p,preamble,PREAMBLE_LEN); 
			memcpy(buff_p+PREAMBLE_LEN,addr_dest,DEST_LEN); 
			memcpy(buff_p+PREAMBLE_LEN+DEST_LEN,addr_source,SOURCE_LEN); 

			*c=file_back&0xFFFF; 

			memcpy(buff_p+PREAMBLE_LEN+DEST_LEN+SOURCE_LEN,c,FLIE_LENGTH_LEN); 

			read(read_handle,buff_p+PREAMBLE_LEN+DEST_LEN+SOURCE_LEN+FLIE_LENGTH_LEN,(unsigned)file_back); 

			fill(BUFFER_MIN-file_back); 

			memcpy(buff_p+PREAMBLE_LEN+DEST_LEN+SOURCE_LEN+FLIE_LENGTH_LEN+file_back,fill_data,(unsigned)(BUFFER_MIN-file_back)); /* 加入填充码 */ 

			GenerateCRC32(buff_p+PREAMBLE_LEN,DEST_LEN+SOURCE_LEN+FLIE_LENGTH_LEN+BUFFER_MIN); 

			memcpy(buff_p+PREAMBLE_LEN+DEST_LEN+SOURCE_LEN+FLIE_LENGTH_LEN+BUFFER_MIN,fcs,FCS_LEN); 

			write(write_handle,buff_p,buff_length); 

			conditional=0; 

			free(fill_data); 
		} 
		else 
		{ 
			buff_length=PREAMBLE_LEN+DEST_LEN+SOURCE_LEN+FLIE_LENGTH_LEN+file_back+FCS_LEN; 
			buff_p=(char *) malloc(buff_length); 

			memcpy(buff_p,preamble,PREAMBLE_LEN); 
			memcpy(buff_p+PREAMBLE_LEN,addr_dest,DEST_LEN); 
			memcpy(buff_p+PREAMBLE_LEN+DEST_LEN,addr_source,SOURCE_LEN); 

			*c=file_back&0XFFFF; 

			memcpy(buff_p+PREAMBLE_LEN+DEST_LEN+SOURCE_LEN,c,FLIE_LENGTH_LEN); 

			read(read_handle,buff_p+PREAMBLE_LEN+DEST_LEN+SOURCE_LEN+FLIE_LENGTH_LEN,(unsigned)file_back); 

			GenerateCRC32(buff_p+PREAMBLE_LEN,DEST_LEN+SOURCE_LEN+FLIE_LENGTH_LEN+file_back); 

			memcpy(buff_p+PREAMBLE_LEN+DEST_LEN+SOURCE_LEN+FLIE_LENGTH_LEN+file_back,fcs,FCS_LEN); 

			write(write_handle,buff_p,buff_length); 

			conditional=0; 
		} 
	} 

	free(buff_p); 

	close(read_handle); 

	close(write_handle); 
} 

void fill(int x) 
{ 

	fill_data=(char *) malloc(x); 

	setmem(fill_data,x,0x0); /* 函数未完成，测试使用 */ 
} 
void GenerateCRC32(char* DataBuf,unsigned long len) 
{ 
	unsigned long oldcrc32; 
	unsigned long crc32; 
	unsigned long oldcrc; 
	unsigned int charcnt; 
	char crc_c,t; 

	oldcrc32 = 0x00000000; /*初值为0 */ 
	charcnt=0; 

	while (len--) { 
		t= (oldcrc32 >> 24) & 0xFF; /* 要移出的字节的值 */ 
		oldcrc=crc32_table[t]; /* 根据移出的字节的值查表 */ 
		crc_c=DataBuf[charcnt]; /* 新移进来的字节值 */ 
		oldcrc32= (oldcrc32 << 8) | crc_c; /* 将新移进来的字节值添在寄存器末字节中 */ 
		oldcrc32=oldcrc32^oldcrc; /* 将寄存器与查出的值进行xor运算 */ 
		charcnt++; 
	} 

	crc32=oldcrc32; 
	*fcs=crc32; 
} 


unsigned long Reflect(unsigned long ref, char ch) 
{ 
	unsigned long value=0; 
	int i; 

	/* 交换bit0和bit7，bit1和bit6，类推 */ 
	for(i=1;i < (ch+1);i++) 
	{ 
		if(ref & 1) 
		value |= value << (ch - i); 
		ref >>= 1; 
	} 
	return value; 
} 

void init_crc32_table() 
{ 
	unsigned long temp_crc; 
	int i; 
	int j; 

	/* 256个值 */ 
	for(i = 0; i <= 0xFF; i++) 
	{ 
		temp_crc=Reflect(i, 8); 
		crc32_table[i]= temp_crc<< 24; 

		for (j = 0; j < 8; j++) 
		{ 
			unsigned long t1,t2; 
			unsigned long flag=crc32_table[i]&0x80000000; 
			t1=(crc32_table[i] << 1); 

			if(flag==0) 
				t2=0; 
			else 
				t2=ulPolynomial; 

			crc32_table[i] =t1^t2 ; 
		} 

		crc32_table[i] = Reflect(crc32_table[i], 32); 
	} 
}