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fb25b48308
I have a problem with CRC though: sometimes it works, sometimes not, I have no clue why, I must be doing something wrong with the CRC calculation routine...
36 lines
1.2 KiB
C
36 lines
1.2 KiB
C
//-----------------------------------------------------------------------------
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// Routines to compute the CRCs (two different flavours, just for confusion)
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// required for ISO 14443, swiped directly from the spec.
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//-----------------------------------------------------------------------------
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#define CRC_14443_A 0x6363 /* ITU-V.41 */
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#define CRC_14443_B 0xFFFF /* ISO/IEC 13239 (formerly ISO/IEC 3309) */
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static unsigned short UpdateCrc14443(unsigned char ch, unsigned short *lpwCrc)
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{
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ch = (ch ^ (unsigned char) ((*lpwCrc) & 0x00FF));
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ch = (ch ^ (ch << 4));
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*lpwCrc = (*lpwCrc >> 8) ^ ((unsigned short) ch << 8) ^
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((unsigned short) ch << 3) ^ ((unsigned short) ch >> 4);
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return (*lpwCrc);
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}
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static void ComputeCrc14443(int CrcType, BYTE *Data, int Length,
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BYTE *TransmitFirst, BYTE *TransmitSecond)
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{
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unsigned char chBlock;
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unsigned short wCrc=CrcType;
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do {
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chBlock = *Data++;
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UpdateCrc14443(chBlock, &wCrc);
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} while (--Length);
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if (CrcType == CRC_14443_B)
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wCrc = ~wCrc; /* ISO/IEC 13239 (formerly ISO/IEC 3309) */
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*TransmitFirst = (BYTE) (wCrc & 0xFF);
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*TransmitSecond = (BYTE) ((wCrc >> 8) & 0xFF);
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return;
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}
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