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

#include "utils.h"
#include "bitmanip.h"

// USART
// Table 20-1 : Baud Rate Calculation
#define USART_BAUDRATE			115200
#define BAUD_PRESCALER			(DIV_ROUND_CLOSEST(F_CPU, (16 * USART_BAUDRATE)) - 1)
// Table 20-8 : Mode Selection (USART Mode SELect)
#define ASYNCHRONOUS			(0<<UMSEL01 | 0<<UMSEL00)
#define SYNCHRONOUS				(0<<UMSEL01 | 1<<UMSEL00)
// Table 20-9 : Parity Bit Selection (USART Parity Mode)
#define PARITY_DISABLED			(0<<UPM01 | 0<<UPM00)
#define PARITY_EVEN				(1<<UPM01 | 0<<UPM00)
#define PARITY_ODD				(1<<UPM01 | 1<<UPM00)
// Table 20-10 : Stop Bit Selection (USART Stop Bit Select)
#define STOP_ONE_BIT			(0<<USBS0)
#define STOP_TWO_BIT			(1<<USBS0)
// Table 20-11 : Data Bit Selection (USART Character SiZe)
#define DATA_FIVE_BIT			(0<<UCSZ02 | 0<<UCSZ01 | 0<<UCSZ00)
#define DATA_SIX_BIT			(0<<UCSZ02 | 0<<UCSZ01 | 1<<UCSZ00)
#define DATA_SEVEN_BIT			(0<<UCSZ02 | 1<<UCSZ01 | 0<<UCSZ00)
#define DATA_EIGHT_BIT			(0<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
#define DATA_NINE_BIT			(1<<UCSZ02 | 1<<UCSZ01 | 1<<UCSZ00)
// 20.11.3 : USART Control and Status Register B (UCSRnB)
#define RECEIVER_DISABLED		(0<<RXEN0)
#define RECEIVER_ENABLED		(1<<RXEN0)
#define TRANSMITTER_DISABLED	(0<<TXEN0)
#define TRANSMITTER_ENABLED		(1<<TXEN0)

// END MACROS

// 20.4 Frame Formats : 8N1 : 8 data bits, no parity, 1 stop bit
// 20.5 USART Initialization : (1) setting baud rate, (2) setting frame format, (3) enabling the Transmitter or the Receiver
void uart_init() {
	UBRR0H = (unsigned char) (BAUD_PRESCALER >> 8);								// 20.11.5 : UBRRnL and UBRRnH – USART Baud Rate Registers
	UBRR0L = (unsigned char) BAUD_PRESCALER;

	UCSR0C |= ASYNCHRONOUS | PARITY_DISABLED | STOP_ONE_BIT | DATA_EIGHT_BIT;	// 20.11.4 : set Frame Format
	
	UCSR0B |= RECEIVER_DISABLED | TRANSMITTER_ENABLED;							// 20.11.3 : enable Receiver and/or Transmitter
}

void uart_tx(char c) {
	while (TEST(UCSR0A, UDRE0) == 0);											// 20.11.2 : do nothing until UDR emission buffer is empty, if UDREn flag is 1, UCSRnA register is empty
	UDR0 = (unsigned char) c;													// 20.11.1 : Put data into buffer, UDRn – USART I/O Data Register (read and write)
}

// write Z on serial port, at a 1Hz frequency
// `screen /dev/ttyUSB0 115200`
int main() {
	uart_init();
	while (1) {
		uart_tx('Z');
		_delay_ms(1000);
	}
}
