About boot loader at mega128

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#include <mega128a.h>
#include <stdio.h>
#include <stdlib.h>
 
 
 
#ifndef RXB8
#define RXB8 1
#endif
 
#ifndef TXB8
#define TXB8 0
#endif
 
#ifndef UPE
#define UPE 2
#endif
 
#ifndef DOR
#define DOR 3
#endif
 
#ifndef FE
#define FE 4
#endif
 
#ifndef UDRE
#define UDRE 5
#endif
 
#ifndef RXC
#define RXC 7
#endif
 
#define FRAMING_ERROR (1<<FE)
#define PARITY_ERROR (1<<UPE)
#define DATA_OVERRUN (1<<DOR)
#define DATA_REGISTER_EMPTY (1<<UDRE)
#define RX_COMPLETE (1<<RXC)
 
// USART0 Receiver buffer
#define RX_BUFFER_SIZE0 8
char rx_buffer0[RX_BUFFER_SIZE0];
 
#if RX_BUFFER_SIZE0 <= 256
unsigned char rx_wr_index0,rx_rd_index0,rx_counter0;
#else
unsigned int rx_wr_index0,rx_rd_index0,rx_counter0;
#endif
 
// This flag is set on USART0 Receiver buffer overflow
bit rx_buffer_overflow0;
 
// USART0 Receiver interrupt service routine
interrupt [USART0_RXC] void usart0_rx_isr(void)
{
char status,data;
status=UCSR0A;
data=UDR0;
if ((status & (FRAMING_ERROR | PARITY_ERROR | DATA_OVERRUN))==0)
   {
   rx_buffer0[rx_wr_index0++]=data;
#if RX_BUFFER_SIZE0 == 256
   // special case for receiver buffer size=256
   if (++rx_counter0 == 0) rx_buffer_overflow0=1;
#else
   if (rx_wr_index0 == RX_BUFFER_SIZE0) rx_wr_index0=0;
   if (++rx_counter0 == RX_BUFFER_SIZE0)
      {
      rx_counter0=0;
      rx_buffer_overflow0=1;
      }
#endif
   }
}
 
#ifndef _DEBUG_TERMINAL_IO_
// Get a character from the USART0 Receiver buffer
#define _ALTERNATE_GETCHAR_
#pragma used+
char getchar(void)
{
char data;
while (rx_counter0==0);
data=rx_buffer0[rx_rd_index0++];
#if RX_BUFFER_SIZE0 != 256
if (rx_rd_index0 == RX_BUFFER_SIZE0) rx_rd_index0=0;
#endif
#asm("cli")
--rx_counter0;
#asm("sei")
return data;
}
#pragma used-
#endif
 
// USART0 Transmitter buffer
#define TX_BUFFER_SIZE0 8
char tx_buffer0[TX_BUFFER_SIZE0];
 
#if TX_BUFFER_SIZE0 <= 256
unsigned char tx_wr_index0,tx_rd_index0,tx_counter0;
#else
unsigned int tx_wr_index0,tx_rd_index0,tx_counter0;
#endif
 
// USART0 Transmitter interrupt service routine
interrupt [USART0_TXC] void usart0_tx_isr(void)
{
if (tx_counter0)
   {
   --tx_counter0;
   UDR0=tx_buffer0[tx_rd_index0++];
#if TX_BUFFER_SIZE0 != 256
   if (tx_rd_index0 == TX_BUFFER_SIZE0) tx_rd_index0=0;
#endif
   }
}
 
#ifndef _DEBUG_TERMINAL_IO_
// Write a character to the USART0 Transmitter buffer
#define _ALTERNATE_PUTCHAR_
#pragma used+
void putchar(char c)
{
while (tx_counter0 == TX_BUFFER_SIZE0);
#asm("cli")
if (tx_counter0 || ((UCSR0A & DATA_REGISTER_EMPTY)==0))
   {
   tx_buffer0[tx_wr_index0++]=c;
#if TX_BUFFER_SIZE0 != 256
   if (tx_wr_index0 == TX_BUFFER_SIZE0) tx_wr_index0=0;
#endif
   ++tx_counter0;
   }
else
   UDR0=c;
#asm("sei")
}
#pragma used-
#endif
 
// Standard Input/Output functions
#include <stdio.h>
 
// Declare your global variables here
 
void main(void)
{
unsigned char h;
char data;
char a[10];
 
PORTD=0x00;
DDRD=0x01;
 
// USART0 initialization
// Communication Parameters: 8 Data, 1 Stop, No Parity
// USART0 Receiver: On
// USART0 Transmitter: On
// USART0 Mode: Asynchronous
// USART0 Baud Rate: 9600
UCSR0A=0x00;
UCSR0B=0xD8;
UCSR0C=0x06;
UBRR0H=0x00;
UBRR0L=0x67;
 
 
#asm("sei")
 
putchar ('A');
 
 
 
 
while (1)
      { 
      if (data=='A')
      {
            a=='B';
            gets (a,10);
      }
            
      
      
      }
}