make_crc.c

abstract rtos

#include "syscfg.h"
#include "aos.h"

#define CRC16_POLY      0x1021      /* CRC-CCITT 16 is based on the polynomial x^16+x^12+x^5+1,
                                       and the reference value is 0x1021 */
U16     crc_tab[256];               
U8      gucIsTableInit;

extern VOID clear_watch_dog(VOID);


VOID init_crc_tab( VOID )
{
    U16     i, j;
    U16     value;



    if ( gucIsTableInit )
        return;

    for ( i=0; i<256; i++ )
    {
        value = (U16)(i << 8);
        for ( j=0; j<8; j++ )
        {
            if ( (value&0x8000) != 0 )
                value = (U16)((value<<1) ^ CRC16_POLY);
            else
                value <<= 1;
        }

        crc_tab[i] = value;
    }
    gucIsTableInit = 1;

}


VOID make_crc( U8 *buffer, U32 count, U16 *crc )
{
    U16 temp;

    temp = *crc;

    while ( count-- != 0 )
    {
        if (count % 10000 == 0)
        {
            clear_watch_dog();
        }
        temp = (U16)(( temp<<8 ) ^ crc_tab[ ( temp>>8 ) ^ *buffer++ ]);
    }

    *crc = temp;
    return ;
}


U16 aos_CalCRC ( U8 *ptr, U32 count )
 {
    U16 crc = 0;

    init_crc_tab();
    make_crc( ptr, count, &crc );
    return  ( crc & 0xFFFF ) ;
}