CRC（循环冗余校验）

1. CRC 循环冗余校验在线计算器

http://www.ip33.com/crc.html

2. 代码

uint16_t CRC16_ModBus(const uint8_t *data, uint16_t length)
{
    const uint16_t POLY = 0xA001;
    uint16_t crc = 0xFFFF;
    
    for (uint16_t i = 0; i < length; i++)
    {
        crc ^= data[i];
        for (uint16_t j = 0; j < 8; j++)
        {
            if ((crc & 0x0001) != 0)
            {
                crc >>= 1;
                crc ^= POLY;
            }
            else
            {
                crc >>= 1;
            }
        }
    }

    return crc;
}

3. 主函数调用

int main(void)
{
	u8 USART_RX_BUF_2[7] = {0x06, 0x00, 0x06, 0x31, 0x02, 0x24, 0x01};
	uint16_t ret = CRC16_ModBus(USART_RX_BUF_2, 7);
	printf("ret：0x%x *******************\r\n", ret);
}

4. 串口日志

5. 串口中断服务函数

/*
 * CRC-16/MODBUS (x16+x15+x2+1): USART_RX_BUF[2 ~ len - 2]  -> USART_RX_BUF[len], USART_RX_BUF[len - 1]
 * eg. receive data: 55 AA 06 00 06 31 02 24 01 FC 80
 *                   55 AA: header
 *                   06: data len (00 06 31 02 24 01)
 *                   01: 1Hz freq
 *                   FC 80: CRC16-MODBUS calculate by data (00 06 31 02 24 01)
 */
void USART1_IRQHandler(void)
{
    if (USART_GetITStatus(USART1, USART_IT_RXNE) != RESET) // determine if it is a receive interrupt, RXNE: RX not empty
    {
        uint8_t data = USART_ReceiveData(USART1);

        if (rx_index == 0 && data != 0x55) // USART_RX_BUF[0] must be 0x55
        {
            return;
        }
        else if (rx_index == 1 && data != 0xAA) // USART_RX_BUF[1] must be 0xAA
        {
            rx_index = 0;
            return;
        }
        else if (rx_index == 2) // USART_RX_BUF[2] is receive data length
        {
            if (data == 0 || data > (USART_REC_LEN - 5)) // data len is illegal
            {
                rx_index = 0;
                return;
            }
        }

        USART_RX_BUF[rx_index] = data; // save the received data to a buffer (USART_RX_BUF)
        rx_index++;

        if (rx_index == (USART_RX_BUF[2] + 5)) // received data len is expected, 5 = 0x55 + 0xAA + buff[2] + CRC(buf[len - 1], buf[len - 2])
        {
            // 进行 CRC 校验
            uint16_t crc = 0xFFFF;
            for (uint16_t i = 2; i < (rx_index - 2); i++)
            {
                crc ^= USART_RX_BUF[i];
                for (uint16_t j = 0; j < 8; j++)
                {
                    if ((crc & 0x0001) != 0)
                    {
                        crc >>= 1;
                        crc ^= 0xA001;
                    }
                    else
                    {
                        crc >>= 1;
                    }
                }
            }
            uint16_t crc_received = USART_RX_BUF[rx_index - 2] | (USART_RX_BUF[rx_index - 1] << 8);
            if (crc_received != crc) // CRC 校验失败
            {
                rx_index = 0;
                return;
            }

            // 处理接收到的数据
            for (uint16_t i = 3; i < (rx_index - 2); i++)
            {
                // 进行相应的处理
            }
            
            rx_index = 0; // 重置数组下标，为下次接收做准备
        }
    }
}

6. 使用C 在线编程工具测试CRC接口 – 菜鸟工具

6.1 C 在线工具 | 菜鸟工具

https://c.runoob.com/compile/11/

6.2 在线编程测试CRC 接口

#include <stdio.h>

typedef unsigned char uint8_t;
typedef unsigned short uint16_t;
typedef unsigned int uint32_t;

// 06 00 06 31 02 33 01
uint8_t array[] = {0x06, 0x00, 0x06, 0x31, 0x02, 0x33, 0x01};
uint16_t ret;

uint16_t CRC16_ModBus(const uint8_t *data, uint16_t length)
{
    const uint16_t POLY = 0xA001;
    uint16_t crc = 0xFFFF;
    
    for (uint16_t i = 0; i < length; i++)
    {
        crc ^= data[i];
        for (uint16_t j = 0; j < 8; j++)
        {
            if ((crc & 0x0001) != 0)
            {
                crc >>= 1;
                crc ^= POLY;
            }
            else
            {
                crc >>= 1;
            }
        }
    }

    return crc;
}

int main()
{
	uint8_t len = sizeof(array);
	
	ret = CRC16_ModBus(array, 7);
	printf("ret = 0x%x \n", ret);
   
   return 0;
}

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