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P25 - adds CRC-9 error detection to confirmed PDU message blocks

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dennis.sheirer
2015-01-18 12:43:10 +00:00
parent 35855b08bb
commit 51d6b328bd
6 changed files with 119 additions and 15 deletions
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61
src/edac/CRCP25.java
View File

@@ -51,6 +51,29 @@ public class CRCP25
0x0400, 0x0800, 0x1000, 0x2000, 0x4000, 0x8000
};
/**
* Confirmed Packet Data Unit CRC-9 checksums, generated by:
*
* long[] table = generate( 135, 9, 0x259l, 0x1FF, false, Parity.NONE );
*/
public static final int[] CRC9_CHECKSUMS = new int[]
{
0x1E7, 0x1F3, 0x1F9, 0x1FC, 0x0D2, 0x045, 0x122, 0x0BD, 0x15E, 0x083,
0x141, 0x1A0, 0x0FC, 0x052, 0x005, 0x102, 0x0AD, 0x156, 0x087, 0x143,
0x1A1, 0x1D0, 0x0C4, 0x04E, 0x00B, 0x105, 0x182, 0x0ED, 0x176, 0x097,
0x14B, 0x1A5, 0x1D2, 0x0C5, 0x162, 0x09D, 0x14E, 0x08B, 0x145, 0x1A2,
0x0FD, 0x17E, 0x093, 0x149, 0x1A4, 0x0FE, 0x053, 0x129, 0x194, 0x0E6,
0x05F, 0x12F, 0x197, 0x1CB, 0x1E5, 0x1F2, 0x0D5, 0x16A, 0x099, 0x14C,
0x08A, 0x069, 0x134, 0x0B6, 0x077, 0x13B, 0x19D, 0x1CE, 0x0CB, 0x165,
0x1B2, 0x0F5, 0x17A, 0x091, 0x148, 0x088, 0x068, 0x018, 0x020, 0x03C,
0x302, 0x035, 0x11A, 0x0A1, 0x150, 0x084, 0x06E, 0x01B, 0x10D, 0x186,
0x0EF, 0x177, 0x1BB, 0x1DD, 0x1EE, 0x0DB, 0x16D, 0x1B6, 0x0F7, 0x17B,
0x1BD, 0x1DE, 0x0C3, 0x161, 0x1B0, 0x0F4, 0x056, 0x007, 0x103, 0x181,
0x1C0, 0x0CC, 0x04A, 0x009, 0x104, 0x0AE, 0x07B, 0x13D, 0x19E, 0x0E3,
0x171, 0x1B8, 0x0F0, 0x054, 0x006, 0x02F, 0x117, 0x18B, 0x1C5, 0x1E2,
0x0DD, 0x16E, 0x09B, 0x14D, 0x1A6
};
/**
* CRC-32 checksums for PDU1 ( HEADER + 1 Block ) messages, generated by:
*
@@ -299,6 +322,40 @@ public class CRCP25
return CRC.FAILED_CRC;
}
/**
* Error detection for CRC-9 protected Confirmed Packet Data blocks. These
* data blocks have a slightly complicated structure because the checksum
* is located between bits 7-15, within a 144 bit block. The checksums
* were generated assuming that the message is contiguous from 0 - 134 bits.
* No data correction is performed.
*/
public static CRC checkCRC9( BitSetBuffer message, int messageStart )
{
int calculated = 0x1FF; //Initial fill of all ones
/* Iterate the set bits and XOR running checksum with lookup value */
for (int i = message.nextSetBit( messageStart );
i >= messageStart && i < messageStart + 144;
i = message.nextSetBit( i+1 ) )
{
/* message bits before the CRC */
if( i < ( messageStart + 7 ) )
{
calculated ^= CRC9_CHECKSUMS[ i - messageStart ];
}
/* message bits after the CRC */
else if( i > ( messageStart + 15 ) )
{
calculated ^= CRC9_CHECKSUMS[ i - messageStart - 9 ];
}
}
int checksum = message.getInt( messageStart + 7, messageStart + 15 );
return ( calculated ^ checksum ) == 0 ? CRC.PASSED : CRC.FAILED_CRC;
}
/**
* Performs Galois 24/12/7 error detection and correction against the 12
@@ -375,13 +432,13 @@ public class CRCP25
public static void main( String[] args )
{
String raw = "0010011000001100101001010111110100010101011010011111110010101100001101111111110100000000000000000001001001101001100000010011101000000000000000001000110101001000000000010010011100111111111000110011110000111000011100000000000000001001111001000101101100001010";
String raw = "000000010110100101010001000000000100010100000000000000000010000000011001001011100000000000000000011111110001000101001011100101110000101000110011";
BitSetBuffer message = BitSetBuffer.load( raw );
mLog.debug( "MSG:" + message.toString() );
CRC results = correctPDU1( message );
CRC results = checkCRC9( message, 0 );
mLog.debug( "COR:" + message.toString() );

15
src/edac/CRCUtil.java
View File

@@ -153,10 +153,17 @@ public class CRCUtil
public static void main( String[] args )
{
mLog.debug( "Starting" );
long polynomial = 0xC75l;
long[] table = generate( 12, 11, polynomial, 0x0, true, Parity.NONE );
// String raw = "000000001010001000000000100010100000000000000000010000000011001001011100000000000000000011111110001000101001011100101110000101000110011101101001";
// BitSetBuffer message = BitSetBuffer.load( raw );
//
// long polynomial = 0x259l;
//
// decode( message, 0, 135, polynomial, 9 );
//
// mLog.debug( message.toString() );
long[] table = generate( 135, 9, 0x259l, 0, false, Parity.NONE );
mLog.debug( toCodeArray( table ) );
mLog.debug( "Finished" );
}