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add openbeacon-compatible crc (CCITT-16)

This commit is contained in:
Stefan `Sec` Zehl 2011-07-08 00:10:53 +02:00
parent fc7b630902
commit b0f5c3e9b6
3 changed files with 30 additions and 1 deletions
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3
firmware/Makefile
View File

@ -8,7 +8,7 @@ OBJS = main.o
VPATH +=
OBJS +=
OBJS += basic/basic.o basic/reinvoke_isp.o basic/delayms.o basic/voltage.o
OBJS += basic/keyin.o basic/uuid.o
OBJS += basic/keyin.o basic/uuid.o basic/crc.o
LIBS += core/libcore.a lcd/liblcd.a applications/libapp.a filesystem/libfat.a usb/libusb.a funk/libfunk.a
##########################################################################
@ -106,3 +106,4 @@ $(OUTFILE).elf: $(OBJS) $(SYS_OBJS) $(LIBS) $(LPCFIX) $(LD_TEMP)
.PHONY: $(LD_TEMP) lcd/liblcd.a applications/libapp.a filesystem/libfat.a usb/libusb.a

4
firmware/basic/basic.h
View File

@ -152,4 +152,8 @@ uint16_t GetUUID16(void);
// for core/iap/iap.c (no official definition)
void iap_entry(uint32_t param_tab[], uint32_t result_tab[]);
// crc.c
uint16_t crc16(char * buf, int len);
#endif

24
firmware/basic/crc.c Normal file
View File

@ -0,0 +1,24 @@
#include "basic.h"
// Calculate the CRC for transmitted and received data using
// the CCITT 16bit algorithm (X^16 + X^12 + X^5 + 1).
uint16_t crc16(char * buf, int len){
unsigned int crc=0xffff;
for(int i=0;i<len;i++){
crc = (unsigned char)(crc >> 8) | (crc << 8);
crc ^= buf[i];
crc ^= (unsigned char)(crc & 0xff) >> 4;
crc ^= (crc << 8) << 4;
crc ^= ((crc & 0xff) << 4) << 1;
};
return crc;
};
/* Note:
It is best not to alter this code. For example, (crc<<8)<<4 does
not generate the same code as crc<<12. Although the result of the
computation is the same, the latter generates much more code and
executes slower.
*/