在Arduino上实现CRC8以写入MLX90614

问题描述

更新:我什至无法获得此计算器来重现所示的SMBus PEC在此数据表的图8和9中>！

UPDATE: I can't even get this calculator to reproduce the SMBus PECs illustrated in figures 8 and 9 of this datasheet!

因此，我正在将arduino与Melexis温度传感器连接，并且一切正常-除了我似乎无法使CRC检查正常工作之外.

So I'm interfacing an arduino with a Melexis temperature sensor, and it's going okay--aside from the fact that I can't seem to get the CRC check to work.

我已经成功完成了读取操作(尽管我的软件忽略了数据包错误代码)，但是我尝试了许多CRC8的实现来检查PEC字节无济于事.我现在使用的代码块来自OneWire:

I've gotten read operations to complete successfully (although my software ignores the packet error code) but I have tried a lot of implementations of CRC8 to check the PEC byte to no avail. The code block I am using now came from OneWire:

uint8_t OneWire::crc8(const uint8_t *addr, uint8_t len)
{
    uint8_t crc = 0;

    while (len--) {
        uint8_t inbyte = *addr++;
        for (uint8_t i = 8; i; i--) {
            uint8_t mix = (crc ^ inbyte) & 0x01;
            crc >>= 1;
            if (mix) crc ^= 0x8C;
            inbyte >>= 1;
        }
    }
    return crc;
}

我改写为只考虑一个字节:

I rewrote it to consider just the one byte:

int smbCRC(int message) {

    uint8_t crc = 0;

  uint8_t inbyte = message & 0xFF;
  for (uint8_t i = 8; i; i--) {
    uint8_t mix = (crc ^ inbyte) & 0x01;
    crc >>= 1;
    if (mix) crc ^= 0x8C;
    inbyte >>= 1;
  }

    return crc;
}

但是其CRC与MLX数据表的CRC不匹配(来自此处).当我像这样用CRC8打印int时:

But its CRC does not match that of the MLX datasheet (Figure 8 from here for example). When I print an int with its CRC8 like so:

int message = 0x3aD2;
lcd.print(String(message,HEX) + " " + String(smbCRC(message),HEX));

尽管数据表显示正确的PEC为0x30，但我仍返回"3ad2 eb".我要去哪里错了?看来这可能是由于CRC的执行错误或我对CRC输入的错误假设所致，而且我不确定从哪里开始进行故障排除.

I get back "3ad2 eb", though the datasheet says the correct PEC is 0x30. Where am I going wrong? It seems like this could be caused by a bad implementation of CRC or bad assumptions on my part about the CRC input, and I'm not sure where to start troubleshooting.

推荐答案

我尚未检查您的CRC实现，但MLX数据表中存在错误，或者至少写得不好.您必须包括所有I2C帧的数据，以便进行PEC的计算，而不仅仅是答复的数据.对于读字命令，您必须包括[SA_W，Command，SA_R，LSB，MSB]，对于写字命令[SA_W，Command，LSB，MSB].

I haven't checked your CRC implementation but there is a mistake in the MLX datasheet or at least it's badly written. You have to include all the I2C frame's data for the PEC's calculation not just the replied data.For a read word command you have to include [SA_W, Command, SA_R, LSB, MSB] and for a write word command [SA_W, Command, LSB, MSB].

因此，对于他们的第一个示例，必须在[0xB4，0x07，0xB5，0xD2，0x3A]上进行计算，而不仅仅是在[0xD2，0x3A]上进行计算，这样您就可以得到预期的0x30.

So, for their first example the calculation must be made on [ 0xB4, 0x07, 0xB5, 0xD2, 0x3A ] and not just on [ 0xD2, 0x3A ] and this way you get the expected 0x30.

这是带有查找表的CRC的简单C实现(非Arduino，但适应起来必须非常简单):

Here is a simple C implementation of the CRC with a lookup table (non Arduino but it must be quite simple to adapt):

static const uint8_t crc_table[] = {
    0x00, 0x07, 0x0e, 0x09, 0x1c, 0x1b, 0x12, 0x15, 0x38, 0x3f, 0x36, 0x31,
    0x24, 0x23, 0x2a, 0x2d, 0x70, 0x77, 0x7e, 0x79, 0x6c, 0x6b, 0x62, 0x65,
    0x48, 0x4f, 0x46, 0x41, 0x54, 0x53, 0x5a, 0x5d, 0xe0, 0xe7, 0xee, 0xe9,
    0xfc, 0xfb, 0xf2, 0xf5, 0xd8, 0xdf, 0xd6, 0xd1, 0xc4, 0xc3, 0xca, 0xcd,
    0x90, 0x97, 0x9e, 0x99, 0x8c, 0x8b, 0x82, 0x85, 0xa8, 0xaf, 0xa6, 0xa1,
    0xb4, 0xb3, 0xba, 0xbd, 0xc7, 0xc0, 0xc9, 0xce, 0xdb, 0xdc, 0xd5, 0xd2,
    0xff, 0xf8, 0xf1, 0xf6, 0xe3, 0xe4, 0xed, 0xea, 0xb7, 0xb0, 0xb9, 0xbe,
    0xab, 0xac, 0xa5, 0xa2, 0x8f, 0x88, 0x81, 0x86, 0x93, 0x94, 0x9d, 0x9a,
    0x27, 0x20, 0x29, 0x2e, 0x3b, 0x3c, 0x35, 0x32, 0x1f, 0x18, 0x11, 0x16,
    0x03, 0x04, 0x0d, 0x0a, 0x57, 0x50, 0x59, 0x5e, 0x4b, 0x4c, 0x45, 0x42,
    0x6f, 0x68, 0x61, 0x66, 0x73, 0x74, 0x7d, 0x7a, 0x89, 0x8e, 0x87, 0x80,
    0x95, 0x92, 0x9b, 0x9c, 0xb1, 0xb6, 0xbf, 0xb8, 0xad, 0xaa, 0xa3, 0xa4,
    0xf9, 0xfe, 0xf7, 0xf0, 0xe5, 0xe2, 0xeb, 0xec, 0xc1, 0xc6, 0xcf, 0xc8,
    0xdd, 0xda, 0xd3, 0xd4, 0x69, 0x6e, 0x67, 0x60, 0x75, 0x72, 0x7b, 0x7c,
    0x51, 0x56, 0x5f, 0x58, 0x4d, 0x4a, 0x43, 0x44, 0x19, 0x1e, 0x17, 0x10,
    0x05, 0x02, 0x0b, 0x0c, 0x21, 0x26, 0x2f, 0x28, 0x3d, 0x3a, 0x33, 0x34,
    0x4e, 0x49, 0x40, 0x47, 0x52, 0x55, 0x5c, 0x5b, 0x76, 0x71, 0x78, 0x7f,
    0x6a, 0x6d, 0x64, 0x63, 0x3e, 0x39, 0x30, 0x37, 0x22, 0x25, 0x2c, 0x2b,
    0x06, 0x01, 0x08, 0x0f, 0x1a, 0x1d, 0x14, 0x13, 0xae, 0xa9, 0xa0, 0xa7,
    0xb2, 0xb5, 0xbc, 0xbb, 0x96, 0x91, 0x98, 0x9f, 0x8a, 0x8d, 0x84, 0x83,
    0xde, 0xd9, 0xd0, 0xd7, 0xc2, 0xc5, 0xcc, 0xcb, 0xe6, 0xe1, 0xe8, 0xef,
    0xfa, 0xfd, 0xf4, 0xf3
};

uint8_t
crc8(uint8_t *p, uint8_t len)
{
        uint16_t i;
        uint16_t crc = 0x0;

        while (len--) {
                i = (crc ^ *p++) & 0xFF;
                crc = (crc_table[i] ^ (crc << 8)) & 0xFF;
        }

        return crc & 0xFF;
}

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