54 lines
1.3 KiB
NASM
54 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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; ***************************************************************************
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; defines
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.equ CRC8_POLYNOMIAL = 0x97 ; HD=4 up to 119 bytes, e.g. detects all 1 to 3 bit errors
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.cseg
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; ---------------------------------------------------------------------------
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; calc crc8 checksum using given polynomial
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;
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; IN:
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; - X : pointer to data to calc crc8 for
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; - r18: number of bytes to calc crc8 for
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; OUT:
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; - r16: crc8 checksum
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; - X : point directly behind the checked area
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; MODIFIED REGS: R16, R17, R18, R19, R20, X
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crc8Calc:
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ldi r16, 0xff ; crc
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ldi r19, CRC8_POLYNOMIAL
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crc8Calc_loop1:
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ld r17, X+ ; running var
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eor r16, r17
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ldi r20, 8 ; counter for loop2
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crc8Calc_loop2:
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lsl r16
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brcc crc8Calc_l1
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eor r16, r19
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crc8Calc_l1:
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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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