110 lines
3.1 KiB
NASM
110 lines
3.1 KiB
NASM
; ***************************************************************************
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; copyright : (C) 2026 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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#ifndef AQH_AVR_NETWORK_MSG_CRC_ASM
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#define AQH_AVR_NETWORK_MSG_CRC_ASM
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; ---------------------------------------------------------------------------
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; @routine NETMSG_CalcAndAddChecksumByte @global
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;
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; @return CFLAG set if okay, clear otherwise
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; @return X points behind checksum byte pos upon return
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; @param X pointer to packet buffer (points behind checksum upon return)
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; @clobbers R16, R17, R18, R19, R20, X
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NETMSG_CalcAndAddChecksumByte:
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rcall netMsgCalcMsgChecksum ; (R16, R17, R18, R19, R20, X)
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st X+, r16 ; add checksum byte
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sec
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ret
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; @end
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; ---------------------------------------------------------------------------
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; @routine NETMSG_CheckMessageInBuffer
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;
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; check message in buffer
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;
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; @return CFLAG set if okay, clear otherwise
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; @param X pointer to packet buffer
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; @clobbers R16, R17 (R18, R19, R20, X)
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NETMSG_CheckMessageInBuffer:
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rcall netMsgCalcMsgChecksum ; (R16, R17, R18, R19, R20, X)
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ld r17, X
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cp r16, r17 ; should be equal
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brne netMsgCheckMessageInBuffer_error
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sec
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ret
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netMsgCheckMessageInBuffer_error:
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clc
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ret
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; @end
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; ---------------------------------------------------------------------------
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; @routine netMsgCalcMsgChecksum
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;
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; calc checksum from msg buffer (except crc byte)
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;
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; @return r16 crc8 checksum
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; @return X points to position of checksum byte
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; @param X pointer to packet buffer (points to checksum byte upon return)
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; @clobbers R18 (R16, R17, R19, R20, X)
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netMsgCalcMsgChecksum:
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adiw xh:xl, NETMSG_OFFS_MSGLEN
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ld r18, X ; read msg len
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sbiw xh:xl, NETMSG_OFFS_MSGLEN
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inc r18 ; account for dest address
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inc r18 ; account for msg len byte
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rjmp netMsgCrcCalc ; (R16, R17, R18, R19, R20, X)
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; @end
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; ---------------------------------------------------------------------------
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; @routine netMsgCrcCalc @global
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; calc checksum using given polynomial
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;
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; @return r16 calculated 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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; @clobbers R16, R17, R18, R19, R20, X
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netMsgCrcCalc:
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ldi r16, 0xff ; start crc
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ldi r19, NETMSG_CRC8_POLYNOMIAL
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netMsgCrcCalc_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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netMsgCrcCalc_loop2:
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lsl r16
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brcc netMsgCrcCalc_l1
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eor r16, r19
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netMsgCrcCalc_l1:
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dec r20
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brne netMsgCrcCalc_loop2
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dec r18
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brne netMsgCrcCalc_loop1
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ret
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; @end
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#endif
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