CRC32是什么？

CRC32:CRC本身是“冗余校验码”的意思，CRC32则表示会产生一个32bit（8位十六进制数）的校验值。由于CRC32产生校验值时源数据块的每一个bit（位）都参与了计算，所以数据块中即使只有一位发生了变化，也会得到不同的CRC32值.

CRC是一种数据错误检查技术，它可以确保最初写入镜像文件的数据与从镜像文件中使用的数据保持一致。
CRC32表示使用32位来保存错误检查信息，在创建镜像文件的时候，CRC32的详细信息将嵌入到该文件中，以确保在将该文件还原到磁盘时能够检测到它是否已经损坏。

显示CRC32出错，可能镜像文件损坏了

值得注意的是最好不要对Ghost镜像文件所存放的分区进行碎片整理，否则很容易损坏ghost镜像文件。


嵌入式网络通讯，没有CRC校验怎么行呢。
下面是软Crc和STM32片内CRC对比，片内CRC不大好做累加。（出之石头哥）

#include "Sys.h"
#include "conf.h"

static uint DataBuffer[] =
{
    0x00001021, 0x20423063, 0x408450a5, 0x60c670e7, 0x9129a14a, 0xb16bc18c,
    0xd1ade1ce, 0xf1ef1231, 0x32732252, 0x52b54294, 0x72f762d6, 0x93398318,
    0xa35ad3bd, 0xc39cf3ff, 0xe3de2462, 0x34430420, 0x64e674c7, 0x44a45485,
    0xa56ab54b, 0x85289509, 0xf5cfc5ac, 0xd58d3653, 0x26721611, 0x063076d7,
    0x569546b4, 0xb75ba77a, 0x97198738, 0xf7dfe7fe, 0xc7bc48c4, 0x58e56886,
    0x78a70840, 0x18612802, 0xc9ccd9ed, 0xe98ef9af, 0x89489969, 0xa90ab92b,
    0x4ad47ab7, 0x6a961a71, 0x0a503a33, 0x2a12dbfd, 0xfbbfeb9e, 0x9b798b58,
    0xbb3bab1a, 0x6ca67c87, 0x5cc52c22, 0x3c030c60, 0x1c41edae, 0xfd8fcdec,
    0xad2abd0b, 0x8d689d49, 0x7e976eb6, 0x5ed54ef4, 0x2e321e51, 0x0e70ff9f,
    0xefbedfdd, 0xcffcbf1b, 0x9f598f78, 0x918881a9, 0xb1caa1eb, 0xd10cc12d,
    0xe16f1080, 0x00a130c2, 0x20e35004, 0x40257046, 0x83b99398, 0xa3fbb3da,
    0xc33dd31c, 0xe37ff35e, 0x129022f3, 0x32d24235, 0x52146277, 0x7256b5ea,
    0x95a88589, 0xf56ee54f, 0xd52cc50d, 0x34e224c3, 0x04817466, 0x64475424,
    0x4405a7db, 0xb7fa8799, 0xe75ff77e, 0xc71dd73c, 0x26d336f2, 0x069116b0,
    0x76764615, 0x5634d94c, 0xc96df90e, 0xe92f99c8, 0xb98aa9ab, 0x58444865,
    0x78066827, 0x18c008e1, 0x28a3cb7d, 0xdb5ceb3f, 0xfb1e8bf9, 0x9bd8abbb,
    0x4a755a54, 0x6a377a16, 0x0af11ad0, 0x2ab33a92, 0xed0fdd6c, 0xcd4dbdaa,
    0xad8b9de8, 0x8dc97c26, 0x5c644c45, 0x3ca22c83, 0x1ce00cc1, 0xef1fff3e,
    0xdf7caf9b, 0xbfba8fd9, 0x9ff86e17, 0x7e364e55, 0x2e933eb2, 0x0ed11ef0
};

u8 inited = 0;

void Init()
{
  /* Enable CRC clock */
  RCC->AHBENR |= RCC_AHBPeriph_CRC;
  
  inited = 1;
}

// 硬件实现的Crc
uint SUPPORT_ComputeCRC2( const void* rgBlock, int len, uint crc )
{
    uint* ptr = (uint*)rgBlock;

        if (!inited) Init();
        
    len >>= 2;
    CRC_ResetDR();
    // STM32的初值是0xFFFFFFFF，而软Crc初值是0
        CRC->DR = crc ^ 0xFFFFFFFF;
    //CRC->DR = 0xFFFFFFFF;
    while(len-- > 0)
    {
        CRC->DR =__REV(*ptr++);    //字节顺序倒过来,注意不是位序,不是用__RBIT指令
    }
    return CRC->DR;
    //UINT32 rs = CRC->DR;
    //return c_CRCTable[ ((crc >> 24) ^ rs) & 0xFF ] ^ (crc << 8);
}

void TestCrc()
{
    debug_printf("\r\n\r\n");
    debug_printf("TestCrc Start......\r\n");

    uint size = ArrayLength(DataBuffer);
    
        // SUPPORT_ComputeCRC是软校验，SUPPORT_ComputeCRC2是硬件实现，要求硬件实现的结果跟软件实现一致
        uint crc = Sys.Crc(DataBuffer, size*4, 0);
        uint crc2 = SUPPORT_ComputeCRC2(DataBuffer, size*4, 0);
        debug_printf("CRC1:0x%08x  CRC2:0x%08x \r\n", crc, crc2);
        
        uint data = 0xA5A5A5A5;
        crc = Sys.Crc(&data, 4, 0);
        crc2 = SUPPORT_ComputeCRC2(&data, 4, 0);
        // 要求crc==crc2
        debug_printf("CRC1:0x%08x  CRC2:0x%08x \r\n", crc, crc2);

        // 增量计算CRC
        crc = Sys.Crc(DataBuffer, size*4, 1234);
        crc2 = SUPPORT_ComputeCRC2(DataBuffer, size*4, 1234);
        // 要求crc==crc2
        debug_printf("CRC1:0x%08x  CRC2:0x%08x \r\n", crc, crc2);
    
    debug_printf("\r\nTestFlash Finish!\r\n");
}

SmartOS的实现代码：

//
// CRC 32 table for use under ZModem protocol, IEEE 802
// G(x) = x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1
//
static const uint c_CRCTable[ 256 ] =
{
    0x00000000, 0x04C11DB7, 0x09823B6E, 0x0D4326D9, 0x130476DC, 0x17C56B6B, 0x1A864DB2, 0x1E475005,
    0x2608EDB8, 0x22C9F00F, 0x2F8AD6D6, 0x2B4BCB61, 0x350C9B64, 0x31CD86D3, 0x3C8EA00A, 0x384FBDBD,
    0x4C11DB70, 0x48D0C6C7, 0x4593E01E, 0x4152FDA9, 0x5F15ADAC, 0x5BD4B01B, 0x569796C2, 0x52568B75,
    0x6A1936C8, 0x6ED82B7F, 0x639B0DA6, 0x675A1011, 0x791D4014, 0x7DDC5DA3, 0x709F7B7A, 0x745E66CD,
    0x9823B6E0, 0x9CE2AB57, 0x91A18D8E, 0x95609039, 0x8B27C03C, 0x8FE6DD8B, 0x82A5FB52, 0x8664E6E5,
    0xBE2B5B58, 0xBAEA46EF, 0xB7A96036, 0xB3687D81, 0xAD2F2D84, 0xA9EE3033, 0xA4AD16EA, 0xA06C0B5D,
    0xD4326D90, 0xD0F37027, 0xDDB056FE, 0xD9714B49, 0xC7361B4C, 0xC3F706FB, 0xCEB42022, 0xCA753D95,
    0xF23A8028, 0xF6FB9D9F, 0xFBB8BB46, 0xFF79A6F1, 0xE13EF6F4, 0xE5FFEB43, 0xE8BCCD9A, 0xEC7DD02D,
    0x34867077, 0x30476DC0, 0x3D044B19, 0x39C556AE, 0x278206AB, 0x23431B1C, 0x2E003DC5, 0x2AC12072,
    0x128E9DCF, 0x164F8078, 0x1B0CA6A1, 0x1FCDBB16, 0x018AEB13, 0x054BF6A4, 0x0808D07D, 0x0CC9CDCA,
    0x7897AB07, 0x7C56B6B0, 0x71159069, 0x75D48DDE, 0x6B93DDDB, 0x6F52C06C, 0x6211E6B5, 0x66D0FB02,
    0x5E9F46BF, 0x5A5E5B08, 0x571D7DD1, 0x53DC6066, 0x4D9B3063, 0x495A2DD4, 0x44190B0D, 0x40D816BA,
    0xACA5C697, 0xA864DB20, 0xA527FDF9, 0xA1E6E04E, 0xBFA1B04B, 0xBB60ADFC, 0xB6238B25, 0xB2E29692,
    0x8AAD2B2F, 0x8E6C3698, 0x832F1041, 0x87EE0DF6, 0x99A95DF3, 0x9D684044, 0x902B669D, 0x94EA7B2A,
    0xE0B41DE7, 0xE4750050, 0xE9362689, 0xEDF73B3E, 0xF3B06B3B, 0xF771768C, 0xFA325055, 0xFEF34DE2,
    0xC6BCF05F, 0xC27DEDE8, 0xCF3ECB31, 0xCBFFD686, 0xD5B88683, 0xD1799B34, 0xDC3ABDED, 0xD8FBA05A,
    0x690CE0EE, 0x6DCDFD59, 0x608EDB80, 0x644FC637, 0x7A089632, 0x7EC98B85, 0x738AAD5C, 0x774BB0EB,
    0x4F040D56, 0x4BC510E1, 0x46863638, 0x42472B8F, 0x5C007B8A, 0x58C1663D, 0x558240E4, 0x51435D53,
    0x251D3B9E, 0x21DC2629, 0x2C9F00F0, 0x285E1D47, 0x36194D42, 0x32D850F5, 0x3F9B762C, 0x3B5A6B9B,
    0x0315D626, 0x07D4CB91, 0x0A97ED48, 0x0E56F0FF, 0x1011A0FA, 0x14D0BD4D, 0x19939B94, 0x1D528623,
    0xF12F560E, 0xF5EE4BB9, 0xF8AD6D60, 0xFC6C70D7, 0xE22B20D2, 0xE6EA3D65, 0xEBA91BBC, 0xEF68060B,
    0xD727BBB6, 0xD3E6A601, 0xDEA580D8, 0xDA649D6F, 0xC423CD6A, 0xC0E2D0DD, 0xCDA1F604, 0xC960EBB3,
    0xBD3E8D7E, 0xB9FF90C9, 0xB4BCB610, 0xB07DABA7, 0xAE3AFBA2, 0xAAFBE615, 0xA7B8C0CC, 0xA379DD7B,
    0x9B3660C6, 0x9FF77D71, 0x92B45BA8, 0x9675461F, 0x8832161A, 0x8CF30BAD, 0x81B02D74, 0x857130C3,
    0x5D8A9099, 0x594B8D2E, 0x5408ABF7, 0x50C9B640, 0x4E8EE645, 0x4A4FFBF2, 0x470CDD2B, 0x43CDC09C,
    0x7B827D21, 0x7F436096, 0x7200464F, 0x76C15BF8, 0x68860BFD, 0x6C47164A, 0x61043093, 0x65C52D24,
    0x119B4BE9, 0x155A565E, 0x18197087, 0x1CD86D30, 0x029F3D35, 0x065E2082, 0x0B1D065B, 0x0FDC1BEC,
    0x3793A651, 0x3352BBE6, 0x3E119D3F, 0x3AD08088, 0x2497D08D, 0x2056CD3A, 0x2D15EBE3, 0x29D4F654,
    0xC5A92679, 0xC1683BCE, 0xCC2B1D17, 0xC8EA00A0, 0xD6AD50A5, 0xD26C4D12, 0xDF2F6BCB, 0xDBEE767C,
    0xE3A1CBC1, 0xE760D676, 0xEA23F0AF, 0xEEE2ED18, 0xF0A5BD1D, 0xF464A0AA, 0xF9278673, 0xFDE69BC4,
    0x89B8FD09, 0x8D79E0BE, 0x803AC667, 0x84FBDBD0, 0x9ABC8BD5, 0x9E7D9662, 0x933EB0BB, 0x97FFAD0C,
    0xAFB010B1, 0xAB710D06, 0xA6322BDF, 0xA2F33668, 0xBCB4666D, 0xB8757BDA, 0xB5365D03, 0xB1F740B4
};

uint TSys::Crc(const void* buf, uint len, uint crc)
{
    byte* ptr = (byte*)buf;
    while(len-- > 0)
    {
        crc = c_CRCTable[ ((crc >> 24) ^ (*ptr++)) & 0xFF ] ^ (crc << 8);
    }

    return crc;
}

// 硬件实现的Crc
uint TSys::Crc(const void* buf, uint len)
{
#ifdef STM32F4
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_CRC, ENABLE);
#else
  RCC_AHBPeriphClockCmd(RCC_AHBPeriph_CRC, ENABLE);
#endif

    CRC_ResetDR();
    // STM32的初值是0xFFFFFFFF，而软Crc初值是0
    //CRC->DR = __REV(crc ^ 0xFFFFFFFF);
    //CRC->DR = 0xFFFFFFFF;
    uint* ptr = (uint*)buf;
    len >>= 2;
    while(len-- > 0)
    {
        CRC->DR =__REV(*ptr++);    // 字节顺序倒过来,注意不是位序,不是用__RBIT指令
    }
    uint crc = CRC->DR;

#ifdef STM32F4
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_CRC, DISABLE);
#else
  RCC_AHBPeriphClockCmd(RCC_AHBPeriph_CRC, DISABLE);
#endif

    return crc;
}

static const ushort c_CRC16Table[] =
{
0x0000, 0xCC01, 0xD801, 0x1400, 0xF001, 0x3C00, 0x2800, 0xE401,
0xA001, 0x6C00, 0x7800, 0xB401, 0x5000, 0x9C01, 0x8801, 0x4400,
};

ushort TSys::Crc16(const void* buf, uint len, ushort crc)
{
    if (!buf || !len) return 0;

    for (int i = 0; i < len; i++)
    {
        byte b = ((byte*)buf)[i];
        crc = (ushort)(c_CRC16Table[(b ^ crc) & 0x0F] ^ (crc >> 4));
        crc = (ushort)(c_CRC16Table[((b >> 4) ^ crc) & 0x0F] ^ (crc >> 4));
    }
    return crc;
}