Merge pull request #34 from martinwag/add-custom-crc

Compiler switch enables providing own CRC16 implemetation.

CANopen.c

@@ -52,6 +52,9 @@
    be generated with calloc(). */
 /* #define CO_USE_GLOBALS */
 
+/* If defined, the user provides an own implemetation for calculating the
+ * CRC16 CCITT checksum. */
+/* #define CO_USE_OWN_CRC16 */
 
 #ifndef CO_USE_GLOBALS
     #include <stdlib.h> /*  for malloc, free */

stack/crc16-ccitt.c

@@ -43,6 +43,7 @@
  * to do so, delete this exception statement from your version.
  */
 
+#ifndef CO_USE_OWN_CRC16
 
 #include "crc16-ccitt.h"
 
@@ -114,3 +115,5 @@ unsigned short crc16_ccitt(
     }
     return crc;
 }
+
+#endif /* CO_USE_OWN_CRC16 */

stack/crc16-ccitt.h

@@ -72,6 +72,9 @@
  *
  * @return Calculated CRC.
  */
+#ifdef CO_USE_OWN_CRC16
+extern
+#endif
 unsigned short crc16_ccitt(
         const unsigned char     block[],
         unsigned int            blockLength,