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

// mathematics 
#define DIV_ROUND_CLOSEST(n, d)	((((n) < 0) == ((d) < 0)) ? (((n) + (d)/2)/(d)) : (((n) - (d)/2)/(d))) // https://stackoverflow.com/a/18067292

// stringify
#define STRINGIFY_HELPER(x)		#x
#define STRINGIFY(x)			STRINGIFY_HELPER(x)

// concatenate
#define CONCAT_HELPER(x, y)		x ## y
#define CONCAT(x, y)			CONCAT_HELPER(x, y)

// get argument
#define ARG_1(v1, v2)			v1
#define ARG_2(v1, v2)			v2
#define GET_PORT(args)			ARG_1 args
#define GET_BIT(args)			ARG_2 args
// // version with "LED1 B, D1" without parenthesis
// #define ARG_1(v1, ...)			v1
// #define ARG_2(v1, v2, ...)		v2
// #define GET_PORT(...)			ARG_1(__VA_ARGS__)
// #define GET_BIT(...)			ARG_2(__VA_ARGS__)

// actions on registers
#define SET(register, bit)		register |= 1 << bit
#define CLEAR(register, bit)	register &= ~(1 << bit)
#define TEST(register, bit)		(register & 1 << bit)
#define TOGGLE(register, bit)	register ^= 1 << bit

// actions on elements
#define SET_ELEM(elem)			SET(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
// #define SET_ELEM(...)			SET(CONCAT(PORT, GET_PORT(__VA_ARGS__)), GET_BIT(__VA_ARGS__)) // version for "LED1 B, D1" without parenthesis
#define CLEAR_ELEM(elem)		CLEAR(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
#define TEST_ELEM(elem)			TEST(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
#define TOGGLE_ELEM(elem)		TOGGLE(CONCAT(PORT, GET_PORT(elem)), GET_BIT(elem))
#define MODE_OUTPUT(elem)		SET(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
#define MODE_INPUT(elem)		CLEAR(CONCAT(DDR, GET_PORT(elem)), GET_BIT(elem))
#define TOGGLE_PIN(elem)		SET(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem))
#define TEST_PIN(elem)			(TEST(CONCAT(PIN, GET_PORT(elem)), GET_BIT(elem)))
#define IS_PIN_SET(elem)		(TEST_PIN(elem) == 0)
#define IS_PIN_CLEAR(elem)		(TEST_PIN(elem) == 1)

// bits
#define D1	0
#define D2	1
#define D3	2
#define D4	4
#define SW1	2
#define SW2	4

// elements (port, bit)
// #define LED1	B, D1
#define LED1	(B, D1)
#define LED2	(B, D2)
#define LED3	(B, D3)
#define LED4	(B, D4)
#define BUTTON1	(D, SW1)
#define BUTTON2	(D, SW2)

// 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)

// TIMER
#define PERIOD							2000
#define TIME_MS(ms)						(((F_CPU / PRESCALE_VALUE) * ms) / 1000)
#define PRESCALE_VALUE					1024		// can be 1, 8, 64, 256, 1024
// table 16-5 : prescale sets
#define PRESCALE_SET(value)  \
										((value) == 1   ? (0<<CS12 | 0<<CS11 | 1<<CS10) : \
										 (value) == 8   ? (0<<CS12 | 1<<CS11 | 0<<CS10) : \
										 (value) == 64  ? (0<<CS12 | 1<<CS11 | 1<<CS10) : \
										 (value) == 256 ? (1<<CS12 | 0<<CS11 | 0<<CS10) : \
										 (value) == 1024? (1<<CS12 | 0<<CS11 | 1<<CS10) : \
														  (0<<CS12 | 0<<CS11 | 0<<CS10))
// Table 16-4 : Waveform Generation Mode Bit Description
#define CTC_TOP_OCR1A_IN_TCCR1B			(0<<WGM13 | 1<<WGM12)
#define CTC_TOP_OCR1A_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
#define CTC_TOP_ICR1_IN_TCCR1B			(1<<WGM13 | 1<<WGM12)
#define CTC_TOP_ICR1_IN_TCCR1A									(0<<WGM11 | 0<<WGM10)
#define FAST_PWM_TOP_OCR1A_IN_TCCR1B	(1<<WGM13 | 1<<WGM12)
#define FAST_PWM_TOP_OCR1A_IN_TCCR1A							(1<<WGM11 | 1<<WGM10)
#define FAST_PWM_TOP_ICR1_IN_TCCR1B		(1<<WGM13 | 1<<WGM12)
#define FAST_PWM_TOP_ICR1_IN_TCCR1A								(1<<WGM11 | 0<<WGM10)
// 16.11.8 : Timer/Counter1 Interrupt Mask Register
#define INTERRUPT_ENABLE_CHANNEL_A		(1 << OCIE1A)
#define INTERRUPT_DISABLE_CHANNEL_A		(0 << OCIE1A)

// END MACROS

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_ENABLED | 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 UDRn buffer is empty, (UDREn flag in UCSRnA register set to 1 when buffer empty)
	UDR0 = (unsigned char) c;													// 20.11.1 : Put data into buffer, UDRn – USART I/O Data Register (read and write)
}

char uart_rx(void) {
	while (TEST(UCSR0A, RXC0) == 0);											// 20.11.2 : do nothing until there are unread data in the receive buffer (UDRn), (RXCn flag in UCSRnA register set to 1 when buffer has data)
	return UDR0;																// 20.11.1 : get data in buffer, UDRn – USART I/O Data Register (read and write)
}

// send back caracters received on serial port
// `screen /dev/ttyUSB0 115200`
int main() {
	uart_init();

	char received_char;
	while(1) {
		received_char = uart_rx();
		uart_tx(received_char);
	}
}