avr: provide polynomial for crc function.

avr/modules/com2/crc.asm

@@ -51,16 +51,14 @@ com2CheckMessageInBuffer_error:
 
 
 ; ---------------------------------------------------------------------------
-; com2CalcMsgChecksum
+; @routine com2CalcMsgChecksum
 ;
 ; calc checksum from msg buffer (except crc byte)
 ;
-; IN:
-; - X  : pointer to packet buffer (points to checksum byte upon return)
-; OUT:
-; - r16: crc8 checksum
-; - X  : points to position of checksum byte
-; MODIFIED REGS: R16, R18, (R17, R20, X)
+; @return r16 crc8 checksum
+; @return X   points to position of checksum byte
+; @param X  pointer to packet buffer (points to checksum byte upon return)
+; @clobbers R16, R18, R19, (R17, R20, X)
 
 com2CalcMsgChecksum:
   adiw xh:xl, COM2_MSG_OFFS_MSGLEN
@@ -68,6 +66,8 @@ com2CalcMsgChecksum:
   sbiw xh:xl, COM2_MSG_OFFS_MSGLEN
   inc r18                             ; account for dest address
   inc r18                             ; account for msg len byte
+  ldi r19, COM2_CRC8_POLYNOMIAL       ; polynomial
   rjmp crc8Calc                       ; (R16, R17, R18, R20, X)
+; @end
 
 

avr/modules/com2/defs.asm

@@ -45,3 +45,4 @@
 .equ COM2_ERROR_COLLISION          = 5
 
 
+.equ COM2_CRC8_POLYNOMIAL          = 0x97 ; HD=4 up to 119 bytes, e.g. detects all 1 to 3 bit errors