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piripic
Joined: 15 Jan 2008
Posts: 25
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| Problem with fast CRC16 |
 Posted: Mon Sep 08, 2008 2:14 am |
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Hi,
I am testing the fast CRC16 algorithm, the two functions never return the same result also initializing the variable MyCRC to 0xFFFF, where I mistake ?
Here my test code:
| Code: | #include <18F24K20.h>
#device adc=8
#FUSES NOWDT, HS, NOPROTECT, NOBROWNOUT, NOPUT, NOCPD, STVREN
#FUSES NODEBUG, NOLVP, NOWRT, NOWRTD, IESO, FCMEN, NOPBADEN, WRTC
#FUSES NOWRTB, NOEBTR, NOEBTRB, NOCPB, LPT1OSC, MCLR
#use delay(clock=8000000)
#use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8,errors)
unsigned int16 FSR0;
#locate FSR0 = 0x0FE9
unsigned int8 POSTINC0;
#locate POSTINC0 = 0x0FEE
#define MYDIM 2
int8 MyArray[MYDIM]; // Global Array
int16 crc_1021(int16 old_crc, int8 data)
{
int16 crc;
int16 x;
x = make8(old_crc,1) ^ data; //x = ((old_crc>>8) ^ data) & 0xff;
x ^= x>>4;
crc = (old_crc << 8) ^ (x << 12) ^ (x <<5) ^ x;
crc &= 0xffff;
return crc;
}
//-----------------------------------------------------------------------------
// Calculate the CRC16 value of a specified buffer.
//
// A very fast CRC-16 routine based on the CCITT polynome 0x1021.
// This implementation is very small and fast. Using some specific features of
// the polynome the resulting code is even faster than table driven algorithms.
//
// Original Code: Ashley Roll www.digitalnemesis.com
// Optimisations: Scott Dattalo www.dattalo.com
//-----------------------------------------------------------------------------
int16 Calc_Crc16(int8 *Buffer, int16 Len) // Note: save 5 instructions by
{ // changing 'int16 Len' to 'int8 Len'.
int8 Index;
union
{
int8 uByte[2];
int16 uWord;
} CRC16;
CRC16.uWord = 0xFFFF; // Initialise CRC to 0xFFFF
FSR0 = Buffer; // Copy Buffer address to pointer register FSR0
do
{
#ASM
movf POSTINC0,w // load w with next databyte
xorwf CRC16.uByte[0],w // (a^x):(b^y)
movwf Index //
andlw 0xf0 // W = (a^x):0
swapf Index,f // Index = (b^y):(a^x)
xorwf Index,f // Index = (a^b^x^y):(a^x) = i2:i1
// High byte
movf Index,W
andlw 0xf0
xorwf CRC16.uByte[1],W
movwf CRC16.uByte[0]
rlcf Index,W // use rlf for PIC16
rlcf Index,W // use rlf for PIC16
xorwf CRC16.uByte[0],f
andlw 0xe0
xorwf CRC16.uByte[0],f
swapf Index,F
xorwf Index,W
movwf CRC16.uByte[1]
#ENDASM
} while (--Len);
return CRC16.uWord;
}
// ********** M A I N P r o g . ***********
void main()
{
int8 i;
int16 MyCRC=0;
for(i=0 ; i<MYDIM ; i++) {
MyArray[i] = i+1; // fill the array
}
//----calc CRC16 By C function-----------------
for(i=0 ; i<MYDIM ; i++) {
MyCRC = crc_1021(MyCRC,MyArray[i]);
}
printf("C CRC16 value is %Lu\n\r", MyCRC); // Send the result (C function)
//----calc CRC16 by assembly function----------
MyCRC = Calc_Crc16(&MyArray[0],MYDIM);
printf("ASM CRC16 value is %Lu\n\r", MyCRC); // Send the result (assembly function)
while(1) ;
} |
Any ideas ? thanks
Claudio
Last edited by piripic on Mon Sep 08, 2008 6:53 am; edited 1 time in total |
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piripic
Joined: 15 Jan 2008
Posts: 25
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| resolved |
| Posted: Mon Sep 08, 2008 6:06 am |
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Now is ok; this is the working code:
| Code: | #include <18F24K20.h>
#device adc=8
#FUSES NOWDT, HS, NOPROTECT, NOBROWNOUT, NOPUT, NOCPD, STVREN
#FUSES NODEBUG, NOLVP, NOWRT, NOWRTD, IESO, FCMEN, NOPBADEN, WRTC
#FUSES NOWRTB, NOEBTR, NOEBTRB, NOCPB, LPT1OSC, MCLR
#use delay(clock=8000000)
#use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8,errors)
unsigned int16 FSR0;
#locate FSR0 = 0x0FE9
unsigned int8 POSTINC0;
#locate POSTINC0 = 0x0FEE
#define MYDIM 64
int8 MyArray[MYDIM]; // Global Array
int16 crc_1021(int16 old_crc, int8 data)
{
int16 crc;
int16 x;
x = make8(old_crc,1) ^ data; //x = ((old_crc>>8) ^ data) & 0xff;
x ^= x>>4;
crc = (old_crc << 8) ^ (x << 12) ^ (x <<5) ^ x;
crc &= 0xffff;
return crc;
}
//-----------------------------------------------------------------------------
// Calculate the CRC16 value of a specified buffer.
//
// A very fast CRC-16 routine based on the CCITT polynome 0x1021.
// This implementation is very small and fast. Using some specific features of
// the polynome the resulting code is even faster than table driven algorithms.
//
// Original Code: Ashley Roll www.digitalnemesis.com
// Optimisations: Scott Dattalo www.dattalo.com
//-----------------------------------------------------------------------------
int16 Calc_Crc16(int8 *Buffer, int16 Len) // Note: save 5 instructions by
{ // changing 'int16 Len' to 'int8 Len'.
int8 Index;
union
{
int8 uByte[2];
int16 uWord;
} CRC16;
CRC16.uWord = 0xFFFF; // Initialise CRC to 0xFFFF
FSR0 = Buffer; // Copy Buffer address to pointer register FSR0
do
{
#ASM
movf POSTINC0,w // load w with next databyte
xorwf CRC16.uByte[1],w // (a^x):(b^y)
movwf Index //
andlw 0xf0 // W = (a^x):0
swapf Index,f // Index = (b^y):(a^x)
xorwf Index,f // Index = (a^b^x^y):(a^x) = i2:i1
// High byte
movf Index,W
andlw 0xf0
xorwf CRC16.uByte[0],W
movwf CRC16.uByte[1]
rlcf Index,W // use rlf for PIC16
rlcf Index,W // use rlf for PIC16
xorwf CRC16.uByte[1],f
andlw 0xe0
xorwf CRC16.uByte[1],f
swapf Index,F
xorwf Index,W
movwf CRC16.uByte[0]
#ENDASM
} while (--Len);
return CRC16.uWord;
}
// ********** M A I N P r o g . ***********
void main()
{
int8 i;
int16 MyCRC;
for(i=0 ; i<MYDIM ; i++) {
MyArray[i] = i+1; // fill the array
}
//----calc CRC16 By C function-----------------
MyCRC = 0xFFFF;
for(i=0 ; i<MYDIM ; i++) {
MyCRC = crc_1021(MyCRC,MyArray[i]);
}
printf("C CRC16 value is %Lu\n\r", MyCRC); // Send the result (C function)
//----calc CRC16 by assembly function----------
MyCRC = Calc_Crc16(&MyArray[0],MYDIM);
printf("ASM CRC16 value is %Lu\n\r", MyCRC); // Send the result (assembly function)
while(1) ;
} |
I have inverted the CRC16.uByte index value
Claudio |
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