4e1f08b567
- prepared for use of CRC8 - organized code in more files - recv stats message now contains crc errors and io errors
111 lines
2.6 KiB
NASM
111 lines
2.6 KiB
NASM
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; ***************************************************************************
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; code
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.cseg
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; ---------------------------------------------------------------------------
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; add checksum byte to buffer
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;
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; IN:
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; - X : pointer to packet buffer
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; OUT:
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; - CFLAG: set if okay, clear otherwise
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; MODIFIED REGS: R16, R17, R18, X
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comCalcAndAddChecksumByte:
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adiw xh:xl, COM_MSG_OFFS_MSGLEN
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ld r18, X ; read msg len
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inc r18 ; account for dest address
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inc r18 ; account for msg len bytes
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sbiw xh:xl, COM_MSG_OFFS_MSGLEN
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rcall cproCalcXor ; (R16, R17, R18, 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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; ---------------------------------------------------------------------------
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; check message in buffer
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;
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; IN:
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; - X : pointer to packet buffer
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; OUT:
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; - CFLAG: set if okay, clear otherwise
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; MODIFIED REGS: R16, R17, R18, X
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cproCheckMessageInBuffer:
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adiw xh:xl, COM_MSG_OFFS_MSGLEN
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ld r18, X ; read msg len
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inc r18 ; account for dest address
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inc r18 ; account for msg len bytes
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sbiw xh:xl, COM_MSG_OFFS_MSGLEN
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rcall cproCalcXor ; (R16, R17, R18, X)
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ld r17, X
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cp r16,r17 ; should be equal
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brne cproCheckMessageInBuffer_error
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sec
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ret
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cproCheckMessageInBuffer_error:
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clc
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ret
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; ---------------------------------------------------------------------------
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; calc xor checksum
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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: xor checksum
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; - X : point directly behind the checked area
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; MODIFIED REGS: R16, R17, R18, X
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cproCalcXor:
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clr r16
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cproCalcXor_loop1:
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ld r17, X+
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eor r16, r17
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dec r18
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brne cproCalcXor_loop1
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ret
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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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; - r19: polynomial to use (e.g. 0x97: HD=4 up to 119 bytes, e.g. detects all 1 to 3 bit errors)
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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, R20, X
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cproCalcCrc8:
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ldi r16, 0xff ; crc
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cproCalcCrc8_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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cproCalcCrc8_loop2:
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lsl r16
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brcc cproCalcCrc8_l1
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eor r16, r19
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cproCalcCrc8_l1:
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dec r20
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brne cproCalcCrc8_loop2
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dec r18
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brne cproCalcCrc8_loop1
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ret
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