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avr: refactor ctc calculation code.

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This commit is contained in:
Martin Preuss
2024-09-05 18:48:11 +02:00
parent cea3137b5a
commit 7745accfae
1 changed files with 28 additions and 15 deletions
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43
avr/modules/com2/crc.asm
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@@ -14,19 +14,15 @@
; add checksum byte to buffer
;
; IN:
; - X : pointer to packet buffer
; - X : pointer to packet buffer (points behind checksum upon return)
; OUT:
; - CFLAG: set if okay, clear otherwise
; - X : points behind checksum byte pos upon return
; MODIFIED REGS: R16, R17, R18, R19, X
com2CalcAndAddChecksumByte:
adiw xh:xl, COM2_MSG_OFFS_MSGLEN
ld r18, X ; read msg len
sbiw xh:xl, COM2_MSG_OFFS_MSGLEN
inc r18 ; account for dest address
inc r18 ; account for msg len byte
rcall crc8Calc ; (R16, R17, R18, R20, X)
st X, r16 ; add checksum byte
rcall com2CalcMsgChecksum
st X+, r16 ; add checksum byte
sec
ret
@@ -39,15 +35,10 @@ com2CalcAndAddChecksumByte:
; - X : pointer to packet buffer
; OUT:
; - CFLAG: set if okay, clear otherwise
; MODIFIED REGS: R16, R17, R18, R19, R20, X
; MODIFIED REGS: R16, R17 (R18, R20, X)
com2CheckMessageInBuffer:
adiw xh:xl, COM2_MSG_OFFS_MSGLEN
ld r18, X ; read msg len
sbiw xh:xl, COM2_MSG_OFFS_MSGLEN
inc r18 ; account for dest address
inc r18 ; account for msg len byte
rcall crc8Calc ; (R16, R17, R18, R20, X)
rcall com2CalcMsgChecksum ; R16, R18, (R17, R20, X)
ld r17, X
cp r16, r17 ; should be equal
brne com2CheckMessageInBuffer_error
@@ -58,3 +49,25 @@ com2CheckMessageInBuffer_error:
ret
; ---------------------------------------------------------------------------
; 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)
com2CalcMsgChecksum:
adiw xh:xl, COM2_MSG_OFFS_MSGLEN
ld r18, X ; read msg len
sbiw xh:xl, COM2_MSG_OFFS_MSGLEN
inc r18 ; account for dest address
inc r18 ; account for msg len byte
rjmp crc8Calc ; (R16, R17, R18, R20, X)