47 lines
1.3 KiB
NASM
47 lines
1.3 KiB
NASM
; ***************************************************************************
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; copyright : (C) 2023 by Martin Preuss
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; email : martin@libchipcard.de
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;
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; ***************************************************************************
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; * This file is part of the project "AqHome". *
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; * Please see toplevel file COPYING of that project for license details. *
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; ***************************************************************************
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.cseg
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; ---------------------------------------------------------------------------
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; @routine crc8Calc @global
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; calc crc8 checksum using given polynomial
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;
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; @return r16 crc8 checksum
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; @return X points directly after last checked byte
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; @param X pointer to data to calc crc8 for
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; @param r18 number of bytes to calc crc8 for
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; @param r19 polynomial to use
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; @clobbers: R16, R17, R18, R20, R21, X
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crc8Calc:
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clr r16 ; start crc
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crc8Calc_loop1:
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ld r17, X+ ; running var
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ldi r20, 8 ; counter for loop2
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crc8Calc_loop2: ; r16=crc so far, r17=current inbyte
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mov r21, r16
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lsr r16
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eor r21, r17
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lsr r17
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andi r21, 1
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breq crc8Calc_withoutPoly
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eor r16, r19
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crc8Calc_withoutPoly:
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dec r20
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brne crc8Calc_loop2
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dec r18
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brne crc8Calc_loop1
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ret
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; @end
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