isr uart tx string

#include <avr/io.h>
#include <avr/interrupt.h>



#define BAUD 9600
#define BRC 103 //9600baud

#define tx_buffer_size 128


char serialBuffer[tx_buffer_size];
uint8_t serialReadPosition=0;
uint8_t serialWritePosition=0;

void serialWrite(char c[]);
void serialAppend(char c);

#include <util/delay.h>
#include <avr/interrupt.h>


void serialAppend(char c){

	serialBuffer[serialWritePosition]=c;
	serialWritePosition++;

	if(serialWritePosition>=tx_buffer_size){
		serialWritePosition=0;
	}
}


void serialWrite(char c[]){

	for(uint8_t i=0;i<strlen(c);i++){
		serialAppend(c[i]);
	}

	if (UCSR0A & (1<<UDRE0))
	{
		UDR0=0;
	}

}



void USART_init(){

UBRR0H = (BRC>>8);
UBRR0L = BRC;

UCSR0B|=(1<<TXEN0)|(1<<TXCIE0); //1 bit 8 bit data
//TX setup
UCSR0C |=(1<<UCSZ01)|(1<<UCSZ00);

sei();

}

void send_char(unsigned char data){

	while (!(UCSR0A&(1<<UDRE0)));
	UDR0 =data;

}


int main(void){
USART_init();
_delay_ms(100);
serialWrite("Hello World!");
_delay_ms(2000);
while(1){

}

	return 0;
}



ISR(USART_TX_vect){

	if(serialReadPosition!=serialWritePosition)
	{
		send_char(serialBuffer[serialReadPosition]);
		serialReadPosition++;
	}

	if(serialReadPosition>=tx_buffer_size)
	{
		serialReadPosition=0;
	}
}