Remote Access Control

crc.c File Reference

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Detailed Description

Source file for CRC public and support functions.

This file contains the function implementation for the CRC generation functions. Refer to the crc.h file for more details.

• File: crc.c
• Compiler: IAR EWAVR 4.11B
• Supported devices: ATtiny45/85
• AppNote: AVR411 - Secure Rolling Code Algorithm for Wireless Link

Author:

Atmel Corporation: http://www.atmel.com
Support email: avr@atmel.com

Name

Revision

1193

Date

2006-10-31 14:21:08 +0100 (ti, 31 okt 2006)

Copyright (c) 2006, Atmel Corporation All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

3. The name of ATMEL may not be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY ATMEL ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE EXPRESSLY AND SPECIFICALLY DISCLAIMED. IN NO EVENT SHALL ATMEL BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Definition in file crc.c.

#include "crc.h"
#include "common.h"
#include "config.h"

Include dependency graph for crc.c:

Go to the source code of this file.

Functions
void	calcCRC (byte nextByte)
void	initCRC (void)
Variables
byte	CRCReg [3]

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Function Documentation

void calcCRC

(

byte

nextByte

)

Process one byte of the message. Also used for the last two 0-bytes.

Definition at line 67 of file crc.c.

References CRC_POLY, and CRCReg.

Referenced by transmitTeachMessage().

{
        byte reg0 = CRCReg[0];
        byte reg1 = CRCReg[1];
        byte tempByte = nextByte;
        byte count = 8;
        do {
                if( reg0 >> 7 ) {
                        reg0 = (reg0 << 1) | (reg1 >> 7);
                        reg1 = (reg1 << 1) | (tempByte >> 7);
                        tempByte <<= 1;

                        reg0 ^= CRC_POLY >> 8;
                        reg1 ^= CRC_POLY & 0xff;
                } else {
                        reg0 = (reg0 << 1) | (reg1 >> 7);
                        reg1 = (reg1 << 1) | (tempByte >> 7);
                        tempByte <<= 1;
                }
        } while( --count );

        CRCReg[0] = reg0;
        CRCReg[1] = reg1;
}

void initCRC

(

void

)

Initializes CRCReg before processing a message.

Definition at line 58 of file crc.c.

References CRCReg.

Referenced by transmitTeachMessage().

{
        CRCReg[0] = 0xff;
        CRCReg[1] = 0xff;
        CRCReg[2] = 0x00; // Always 0x00. See comment in crc.h file.
}

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Variable Documentation

byte CRCReg[3]

Stores CRC value during calculation.

Definition at line 54 of file crc.c.

Referenced by calcCRC(), initCRC(), and transmitTeachMessage().