AVR_ATMEGA_USART/avr_usart.c

/*
 * Author: Jake Goodwin
 * Date: 2023
 * Description: Small library to communicate with the AT-09 bluetooth module. 
 */

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/sleep.h>
#include <util/delay.h>
#include "avr_at-09.h"


//#############################
//Globals
//#############################

int main() {
    unsigned char* tx_buffer[16];
    unsigned char* rx_buffer[16];
 
    led_blink();
    led_blink(); 
    led_blink(); 
    _delay_ms(1000);

    init_usart0(); 

    //enable interrupts
    sei();
    
    while(1) {
        led_blink();
    }
    
    return 0;
}



//#############################
//FUNCTIONS
//#############################

/*
 * Input: None
 * Output: None
 * Description: init usart0 hardware in async mode
 */
void init_usart0(void) {
    DDRB |= (1<<TX_DDR)|(0<<RX_DDR);
    PORTD |= (0<<TX_PIN)|(0<<RX_PIN); 
    
    //setup stuff for usart communications.
    
    //set baud rate, this is 9600Baud with a 1Mhz clock
    //so it should be equal to 6 or 0x006
    UBRR0H |= (uint8_t) (BT_UBRR>>8);
    UBRR0L |= (uint8_t) BT_UBRR;
    
    //Enable recv and Transmit pins, overrides other uses.
    //IN the usart control and status register 0B
    UCSR0B = (1<<RXEN0) | (1<<TXEN0);

    //setting the data frame format
    //We leave the 2MSB zero for async serial. And we also don't enable
    //parity bits for now. We set a 2bit stop bit and 8bit char size.
    UCSR0C = (1<<USBS0) | (3<<UCSZ00); 
}


/*
 * Input: a 8bit char
 * Output: None
 * Description: Sends a char over usart0
 */
void tx_usart0(unsigned char data) {
    //first wait for the transmit buffer to be empty
    while(!(UCSR0A & (1<<UDRE0))) {
       ;//Equiv of continue
    }

    //now that it's empty, fill buffer with TX data.
    UDR0 = data;
}



/*
 * Input:None 
 * Output: a 8bit char
 * Description: Recvs a char over usart0
 */
unsigned char rx_usart0(void) {
    //first wait for the data to be received.
    while(!(UCSR0A & (1<<RXC0))) {
        ;//Equiv of continue
    }

    //now return the data
    return (unsigned char) UDR0;
}


/*
 * Input: None
 * Output: None
 * Description: Toggles the pin for the LED indicator.
 */
static void led_blink(void) {
    //Set the DDR for output.
    DDRC |= (1<<LED_PIN);

    PORTC ^= (1<<LED_PIN);
    _delay_ms(250);
    PORTC ^= (1<<LED_PIN);
    _delay_ms(250);
    
}