Fix me code with CRC algorithm

[member_tdh]

Hi all members!
In my project, i want to sent data between 2 AVR via RS232. I using CRC algorithm to corrected data, but my program is running wrong. I have not understand detail about CRC method yet. I post my code received and transmition, anybody pls help me...!?
Thanks all friends !

//This's Transmit Data Routine:

/*****************************************************
Chip type : ATmega8515
Program type : Application
Clock frequency : 8.000000 MHz
Memory model : Small
External SRAM size : 0
Data Stack size : 128
*****************************************************/

#include <mega8515.h>
#include <delay.h>
#include <stdlib.h>

// Standard Input/Output functions
#include <stdio.h>

#define BYTE unsigned char
#define WORD unsigned int

void Init();

BYTE DiemGui, ViTriLed;
WORD msec;

bit bTransToPc=0;

interrupt [TIM1_OVF] void timer1_ovf_isr(void)
{
TCNT1H=0xFF; //interrupt 1ms
TCNT1L=0x83;

if (++msec==1000)
{
msec=0;
if (++DiemGui>10) DiemGui=5;
if (++ViTriLed>6) ViTriLed=1;
bTransToPc=1;
// putchar('B');
// putchar(DiemGui);
// putchar(ViTriLed);
}

}


void Init()
{
PORTA=0xFF;
DDRA=0xFF;

PORTB=0xFF;
DDRB=0xFF;

PORTC=0xFF;
DDRC=0xFF;

PORTD=0xFF;
DDRD=0xFF;

PORTE=0xFF;
DDRE=0xFF;

// Timer/Counter 1 initialization
// Clock source: System Clock
// Clock value: 125.000 kHz
// Mode: Normal top=FFFFh
// OC1A output: Discon.
// OC1B output: Discon.
// Noise Canceler: Off
// Input Capture on Falling Edge
// Timer 1 Overflow Interrupt: On
// Input Capture Interrupt: Off
// Compare A Match Interrupt: Off
// Compare B Match Interrupt: Off
TCCR1A=0x00;
TCCR1B=0x03;
TCNT1H=0x00;
TCNT1L=0x00;
ICR1H=0x00;
ICR1L=0x00;
OCR1AH=0x00;
OCR1AL=0x00;
OCR1BH=0x00;
OCR1BL=0x00;

// Timer(s)/Counter(s) Interrupt(s) initialization
TIMSK=0x80;

// USART initialization
// Communication Parameters: 8 Data, 1 Stop, No Parity
// USART Receiver: On
// USART Transmitter: On
// USART Mode: Asynchronous
// USART Baud rate: 9600
UCSRA=0x00;
UCSRB=0x18;
UCSRC=0x86;
UBRRH=0x00;
UBRRL=0x33;

// Global enable interrupts
#asm("sei")
}

// Declare your global variables here

void main(void)
{
BYTE b1,b2,b3,b4,checksum;
Init();

ViTriLed=1;
DiemGui=5;


while (1)
{
b1=(DiemGui%10)+0x30;
b2=(DiemGui/10)+0x30;
b3=(ViTriLed%10)+0x30;
b4=(ViTriLed/10)+0x30;
checksum=b1^b2^b3^b4;
putchar('B');
putchar(b1);
putchar(b2);
putchar(b3);
putchar(b4);
putchar(checksum);

};
}


//This's Received Data Routine:

BYTE buffer[10];

void main()
{
BYTE i,crc8;

Init();

//received 5-Bytes
for(i=0;i<5;i++) crc8=crc8_calc(buffer, 5);

while(1)
{


}

}


BYTE crc8_calc(BYTE *byt, WORD size )
{
/* Calculate CRC-8 value; uses The CCITT-8 polynomial,
expressed as X^8 + X^5 + X^4 + 1 */

BYTE crc = (BYTE) 0xff;
WORD index;
BYTE b;

for( index=0; index<size; index++)
{
crc ^= byt[index];
for( b=0; b<8; ++b )
{
if( crc & 0x80 )
crc = (crc << 1) ^ 0x31;
else
crc = (crc << 1);
}
}
return crc;
}

Pls anybody explain how is CRC8 work...?
Thanks all!