Atmega328: USART

usart.c

#ifndef F_CPU
    #define F_CPU 16000000
#endif

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

#define BAUD 9600
#define MYUBRR F_CPU/16/BAUD-1

void USART_init(unsigned int ubrr) {
    UBRR0H = (unsigned char)(ubrr >> 8);
    UBRR0L = (unsigned char)ubrr;
    UCSR0B = 1 << RXEN0 | 1 << TXEN0;
    UCSR0C = 0 << USBS0 | 3 << UCSZ00;
}

void USART_transmit( unsigned char data ) {
    while(!(UCSR0A & (1 << UDRE0)));
    UDR0 = data;
}

void USART_transmit_string(const char *data) {
    unsigned char c;
    while(( c = *data++ )) {
        USART_transmit(c);
        _delay_ms(10);
    }
}

why you delay in USART_transmit_string() ?