Basler A600f Manual do Utilizador descarregar pdf (Página 151)

Smart Features

BASLER A600

f 6-17

DRAFT

CRC Checksum Chunk Layout

The CRC checksum is an exception to the normal chunk structure. The CRC chunk is always 32

bits wide and is always the last chunk appended to the image data. The lower 16 bits of the chunk

are filled with the checksum and the upper 16 bits of the chunk are filled with zeros.

Using the Checksum to Check the Data Integrity

When the checksum smart feature is enabled, the following two C functions can be used to check

if an acquired frame contains a valid CRC checksum. The user must pass the acquired image

buffer and the buffer’s length in bytes to the CheckBuffer() function. The CheckBuffer() function

uses the CRC16() function to calculate the checksum.

These two samples are intended to aid you in developing the code for your application. They are

provided solely as examples.

/** \brief Calculates a 16 bit CRC checksum

* \param pData Pointer to the data buffer

* \param nbyLength Size of the buffer in bytes

* \return The CRC checksum

unsigned short CRC16(const unsigned char *pData, unsigned long nbyLength )

{

unsigned long i, j, c, bit;

unsigned long crc = 0;

for (i=0; i<nbyLength; i++) {

c = (unsigned long)*pData++;

for (j=0x80; j; j>>=1) {

bit = crc & 0x8000;

crc <<= 1;

if (c & j) bit^= 0x8000;

if (bit) crc^= 0x1021;

}

return (unsigned short) (crc & 0xffff);

}

Bit Description

[ 0 ... 7 ] CRC Checksum low byte

[ 8 ... 15 ] CRC Checksum high byte

[ 16 ... 23 ] 0x00

[ 24 ... 31 ] 0x00

1 2 ... 146 147 148 149 150 151 152 153 154 155 156 ... 179 180

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Basler A600f Manual do Utilizador Página 151