krishan prajapat / Mbed 2 deprecated COM_MNG_TMTC_SIMPLE_updated

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Dependencies:   mbed-rtos mbed

Fork of COM_MNG_TMTC_SIMPLE by Shreesha S

crc.h@0:f016e9e8d48b, 2015-12-01 (annotated)

Committer:
shreeshas95
Date:
Tue Dec 01 10:56:10 2015 +0000
Revision:
0:f016e9e8d48b
Child:
6:79d422d1ed42
Working without COM_SND_TM

Who changed what in which revision?

UserRevisionLine numberNew contents of line
shreeshas95 0:f016e9e8d48b 1 //EDITS
shreeshas95 0:f016e9e8d48b 2 //changed the initial remainder from 0x0000 to 0xffff according to the standards
shreeshas95 0:f016e9e8d48b 3 //made two seperate functions crc16_gen and crc8_gen
shreeshas95 0:f016e9e8d48b 4
shreeshas95 0:f016e9e8d48b 5 #define TOPBIT16 (1 << 15)
shreeshas95 0:f016e9e8d48b 6 #define TOPBIT8 (1 << 7)
shreeshas95 0:f016e9e8d48b 7 #define POLYNOMIAL16 0x1021
shreeshas95 0:f016e9e8d48b 8 #define POLYNOMIAL8 0xEA
shreeshas95 0:f016e9e8d48b 9
shreeshas95 0:f016e9e8d48b 10 typedef uint16_t crctype16;
shreeshas95 0:f016e9e8d48b 11 crctype16 crc16_gen(const unsigned char message[], unsigned int nBytes){
shreeshas95 0:f016e9e8d48b 12 crctype16 remainder = 0xffff;
shreeshas95 0:f016e9e8d48b 13 int byte;
shreeshas95 0:f016e9e8d48b 14 char bit;
shreeshas95 0:f016e9e8d48b 15
shreeshas95 0:f016e9e8d48b 16 for( byte = 0 ; byte < nBytes ; byte++ ){
shreeshas95 0:f016e9e8d48b 17 /*
shreeshas95 0:f016e9e8d48b 18 Bring the data byte by byte
shreeshas95 0:f016e9e8d48b 19 each time only one byte is brought
shreeshas95 0:f016e9e8d48b 20 0 xor x = x
shreeshas95 0:f016e9e8d48b 21 */
shreeshas95 0:f016e9e8d48b 22 remainder = remainder ^ ( message[byte] << 8 );
shreeshas95 0:f016e9e8d48b 23
shreeshas95 0:f016e9e8d48b 24 for( bit = 8 ; bit > 0 ; bit--){
shreeshas95 0:f016e9e8d48b 25 /*
shreeshas95 0:f016e9e8d48b 26 for each bit, xor the remainder with polynomial
shreeshas95 0:f016e9e8d48b 27 if the MSB is 1
shreeshas95 0:f016e9e8d48b 28 */
shreeshas95 0:f016e9e8d48b 29 if(remainder & TOPBIT16){
shreeshas95 0:f016e9e8d48b 30 remainder = (remainder << 1) ^ POLYNOMIAL16;
shreeshas95 0:f016e9e8d48b 31 /*
shreeshas95 0:f016e9e8d48b 32 each time the remainder is xor-ed with polynomial, the MSB is made zero
shreeshas95 0:f016e9e8d48b 33 hence the first digit of the remainder is ignored in the loop
shreeshas95 0:f016e9e8d48b 34 */
shreeshas95 0:f016e9e8d48b 35 }
shreeshas95 0:f016e9e8d48b 36 else{
shreeshas95 0:f016e9e8d48b 37 remainder = (remainder << 1);
shreeshas95 0:f016e9e8d48b 38 }
shreeshas95 0:f016e9e8d48b 39 }
shreeshas95 0:f016e9e8d48b 40 }
shreeshas95 0:f016e9e8d48b 41
shreeshas95 0:f016e9e8d48b 42 return remainder;
shreeshas95 0:f016e9e8d48b 43 }
shreeshas95 0:f016e9e8d48b 44
shreeshas95 0:f016e9e8d48b 45 typedef uint8_t crctype8;
shreeshas95 0:f016e9e8d48b 46 crctype8 crc8_gen(const unsigned char message[], unsigned int nBytes){
shreeshas95 0:f016e9e8d48b 47
shreeshas95 0:f016e9e8d48b 48 crctype8 remainder = 0xff;
shreeshas95 0:f016e9e8d48b 49
shreeshas95 0:f016e9e8d48b 50 for(int byte = 0 ; byte < nBytes ; byte++ ){
shreeshas95 0:f016e9e8d48b 51 /*
shreeshas95 0:f016e9e8d48b 52 Bring the data byte by byte
shreeshas95 0:f016e9e8d48b 53 each time only one byte is brought
shreeshas95 0:f016e9e8d48b 54 0 xor x = x
shreeshas95 0:f016e9e8d48b 55 */
shreeshas95 0:f016e9e8d48b 56 remainder = remainder ^ ( message[byte] );
shreeshas95 0:f016e9e8d48b 57
shreeshas95 0:f016e9e8d48b 58 for(int bit = 8 ; bit > 0 ; bit--){
shreeshas95 0:f016e9e8d48b 59 /*
shreeshas95 0:f016e9e8d48b 60 for each bit, xor the remainder with polynomial
shreeshas95 0:f016e9e8d48b 61 if the MSB is 1
shreeshas95 0:f016e9e8d48b 62 */
shreeshas95 0:f016e9e8d48b 63 if(remainder & TOPBIT8){
shreeshas95 0:f016e9e8d48b 64 remainder = (remainder << 1) ^ POLYNOMIAL8;
shreeshas95 0:f016e9e8d48b 65 /*
shreeshas95 0:f016e9e8d48b 66 each time the remainder is xor-ed with polynomial, the MSB is made zero
shreeshas95 0:f016e9e8d48b 67 hence the first digit of the remainder is ignored in the loop
shreeshas95 0:f016e9e8d48b 68 */
shreeshas95 0:f016e9e8d48b 69 }
shreeshas95 0:f016e9e8d48b 70 else{
shreeshas95 0:f016e9e8d48b 71 remainder = (remainder << 1);
shreeshas95 0:f016e9e8d48b 72 }
shreeshas95 0:f016e9e8d48b 73 }
shreeshas95 0:f016e9e8d48b 74 }
shreeshas95 0:f016e9e8d48b 75
shreeshas95 0:f016e9e8d48b 76 return remainder;
shreeshas95 0:f016e9e8d48b 77 }