TELECOMMAND MANAGER V1
Dependencies: mbed SLCD mbed-rtos
crc.h@1:df31097c8442, 2015-06-06 (annotated)
- Committer:
- shreeshas95
- Date:
- Sat Jun 06 04:27:40 2015 +0000
- Revision:
- 1:df31097c8442
- Parent:
- 0:b5b370873460
- Child:
- 2:994e741028c7
before namespace (in class format)
Who changed what in which revision?
User | Revision | Line number | New contents of line |
---|---|---|---|
shreeshas95 | 0:b5b370873460 | 1 | #define WIDTH 16 |
shreeshas95 | 0:b5b370873460 | 2 | #define TOPBIT (1 << 15) |
shreeshas95 | 0:b5b370873460 | 3 | #define POLYNOMIAL 0x1021 |
shreeshas95 | 0:b5b370873460 | 4 | |
shreeshas95 | 1:df31097c8442 | 5 | namespace CRC{ |
shreeshas95 | 1:df31097c8442 | 6 | typedef uint16_t crctype; |
shreeshas95 | 1:df31097c8442 | 7 | crctype crcGenerate(const unsigned char message[], int nBytes){ |
shreeshas95 | 0:b5b370873460 | 8 | crctype remainder = 0xffff; |
shreeshas95 | 0:b5b370873460 | 9 | int byte; |
shreeshas95 | 0:b5b370873460 | 10 | char bit; |
shreeshas95 | 0:b5b370873460 | 11 | |
shreeshas95 | 0:b5b370873460 | 12 | for( byte = 0 ; byte < nBytes ; byte++ ){ |
shreeshas95 | 0:b5b370873460 | 13 | /* |
shreeshas95 | 0:b5b370873460 | 14 | Bring the data byte by byte |
shreeshas95 | 0:b5b370873460 | 15 | each time only one byte is brought |
shreeshas95 | 0:b5b370873460 | 16 | 0 xor x = x |
shreeshas95 | 0:b5b370873460 | 17 | */ |
shreeshas95 | 0:b5b370873460 | 18 | remainder = remainder ^ ( message[byte] << (WIDTH-8) ); |
shreeshas95 | 0:b5b370873460 | 19 | |
shreeshas95 | 0:b5b370873460 | 20 | for( bit = 8 ; bit > 0 ; bit--){ |
shreeshas95 | 0:b5b370873460 | 21 | /* |
shreeshas95 | 0:b5b370873460 | 22 | for each bit, xor the remainder with polynomial |
shreeshas95 | 0:b5b370873460 | 23 | if the MSB is 1 |
shreeshas95 | 0:b5b370873460 | 24 | */ |
shreeshas95 | 0:b5b370873460 | 25 | if(remainder & TOPBIT){ |
shreeshas95 | 0:b5b370873460 | 26 | remainder = (remainder << 1) ^ POLYNOMIAL; |
shreeshas95 | 0:b5b370873460 | 27 | /* |
shreeshas95 | 0:b5b370873460 | 28 | each time the remainder is xor-ed with polynomial, the MSB is made zero |
shreeshas95 | 0:b5b370873460 | 29 | hence the first digit of the remainder is ignored in the loop |
shreeshas95 | 0:b5b370873460 | 30 | */ |
shreeshas95 | 0:b5b370873460 | 31 | } |
shreeshas95 | 0:b5b370873460 | 32 | else{ |
shreeshas95 | 0:b5b370873460 | 33 | remainder = (remainder << 1); |
shreeshas95 | 0:b5b370873460 | 34 | } |
shreeshas95 | 0:b5b370873460 | 35 | } |
shreeshas95 | 0:b5b370873460 | 36 | } |
shreeshas95 | 0:b5b370873460 | 37 | |
shreeshas95 | 0:b5b370873460 | 38 | return remainder; |
shreeshas95 | 0:b5b370873460 | 39 | } |
shreeshas95 | 0:b5b370873460 | 40 | }; |