热文：C/C++关于实现CAN信号的获取方法

2023-06-18 15:05:22 来源：脚本之家

CAN基础知识

标准的CAN 数据为8字节，即64位，但是CAN FD的最大数据可为64字节，为512位，其中的帧ID分为标准帧和扩展帧，其中用11位标准帧，用29位表示扩展帧。

CAN 信号

信号具体指的是CAN数据的多少位到多少位间代表一个具体的信号，如5位到16位表示车辆的行驶速度，即完整的CAN数据可以表示多个信号。

(相关资料图)

can信号获取:

#include 
#include 
unsigned char msbmask[] = {
	0xFF, 0xFE, 0xFC, 0xF8,
	0xF0, 0xE0, 0xC0, 0x80
};
unsigned char lsbmask[] = {
	0x01, 0x03, 0x07, 0x0F,
	0x1F, 0x3F, 0x7F, 0xFF
};
#define BITSET(p,n)  ((p) |= (1u <<(n)))
#define BITCLR(p,n)  ((p) &= ~(1u <<(n)))
#define BITGET(i,n)  ((i) & (1u << (n)))
typedef struct {
	unsigned char* can_data_ptr;
	int  len;
	int msb_pos;
	int lsb_pos;
}can_signal;
static can_signal cansingal;
int can_data_assignment(unsigned char* candata, int msbpos, int lsbpos, int lens)
{
	cansingal.can_data_ptr = (unsigned char*)malloc(lens);
	memcpy((void *)cansingal.can_data_ptr, (const void *)candata,lens);
	cansingal.len = lens;
	cansingal.msb_pos = msbpos;
	cansingal.lsb_pos = lsbpos;
	return 0;
 }
unsigned int can_data_transfer_signal()
{
	int a = 0;
	int b = 0;
	int c = 0;
	int d = 0;
	unsigned  int singal = 0;
	printf("%d %d\n", cansingal.lsb_pos, cansingal.msb_pos);
	printf("%02x %02x %02x %02x\n", cansingal.can_data_ptr[0], cansingal.can_data_ptr[1], cansingal.can_data_ptr[2], cansingal.can_data_ptr[3]);
	a = cansingal.lsb_pos / 8;
	b = cansingal.lsb_pos % 8;
	printf("a %d b %d\n", a, b);
	cansingal.can_data_ptr[a] = cansingal.can_data_ptr[a] & msbmask[b];
	c= cansingal.msb_pos / 8;
	d = cansingal.msb_pos % 8;
	printf("c %d d %d\n", c, d);
	cansingal.can_data_ptr[c] = cansingal.can_data_ptr[c] & lsbmask[d];
	printf("%02x %02x %02x %02x\n", cansingal.can_data_ptr[0], cansingal.can_data_ptr[1], cansingal.can_data_ptr[2], cansingal.can_data_ptr[3]);
	for (int i = cansingal.lsb_pos, j = 0; i <= cansingal.msb_pos; ++i, ++j)
	{
		a = i / 8;
		b = i % 8;
		if ( BITGET(cansingal.can_data_ptr[a], b) )
		{
			BITSET(singal, j);
		}
		else
		{
			BITCLR(singal,j);
		}
	}
	return singal;
}
void can_data_free(void)
{
	free(cansingal.can_data_ptr);
	cansingal.len = 0;
	cansingal.lsb_pos = 0;
	cansingal.msb_pos = 0;
	return;
}
int main(int argc, char* argv[])
{
	unsigned char candata[4] = { 0x44, 0xFE, 0x23, 0x81};
	printf("%02x %02x %02x %02x\n", candata[0], candata[1], candata[2], candata[3]);
	can_data_assignment(candata,31,14,4);
	unsigned int c = can_data_transfer_signal();
	can_data_free();
	printf("%d\n", c);
	system("pause");
	return 0;
}

如上图，can数据的其中4字节为0x44,0xFE，0x23,0x81, 分别对应0到32位的数据，现在获取14位到31位的数据，形成具体的信号值。

运行结果：

C语言涉及到知识

位操作、指针与数组的操作、MSB LSB的表索引。

数组与指针关系：

指针操作 +1 即 p + 1是指向下一位的地址，若p指向的类型为int类型，则p+1 指向下一个int类型数据的地址，若p指向的是个结构体，则p+1指向相对应结构体下一个元素的地址。

其中p[i] = *(p+i)

#include 
int main(int argc, char *argv[]){
    int a[] = {1, 3, 5, 7, 9};
    int *p, i, n;
    p = a;
    n = sizeof(a) / sizeof(int);
    printf("%p %p %p\n", a, a+1, a+2);
    for(i = 0; i < n; i++){
        printf("%d %d %d\n", a[i], *(p+i), *(a+i), p[i]);
    }
    puts("");
    return 0;
}