feat(ex03): it works hehe

ex03/src/main.c

@@ -0,0 +1,21 @@
+#include <avr/interrupt.h>
+#include <avr/io.h>
+
+#include "mystd.h"
+#include "timer.h"
+#include "uart.h"
+#include "utils.h"
+
+int main(void) {
+	uart_init();
+	// enable the S_REG
+	SREG  |= _BV(SREG_I);
+	while (true) {
+	}
+}
+
+
+// UART_RX COMPLETE
+void __attribute__((signal)) __vector_18(void) {
+	uart_tx(UDR0);
+}

ex03/src/timer.c

@@ -0,0 +1,38 @@
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include "mystd.h"
+#include "utils.h"
+
+#define PRESCALER 256
+#define TIMER_FREQ (F_CPU / PRESCALER)
+
+// at a high level:
+// Set the OC1B (PB2) pin as output
+// set the TIMER1 mode to COMPARE (CTC)
+// say to compare against OC1A
+// set the value to be compated at X count
+// say the presacler for the timer is 512
+//
+// all these information are on page ~140
+void timer1_init(void) {
+	// Set PB1 (OC1A) as output
+	DDRB   |= _BV(PB1);
+
+	// CTC mode (WGM12 = 1)
+	TCCR1B |= _BV(WGM12);
+
+	// Toggle OC1B on compare match (COM1B0 = 1)
+	// TCCR1A |= _BV(COM1A0);
+
+	// Set compare values
+	OCR1A	= TIMER_FREQ / 2;
+
+	// Start timer with prescaler 256 (CS12)
+	TCCR1B |= _BV(CS12);
+	
+	// set OCR1A interrupt
+	TIMSK1 = _BV(1);
+
+	sei();
+}

ex03/src/uart.c

@@ -0,0 +1,49 @@
+#include "uart.h"
+#include <avr/io.h>
+#include "mystd.h"
+#include "utils.h"
+
+#define BAUD_RATE  115200
+
+#define UBRR_VALUE ((F_CPU / (8UL * BAUD_RATE)) - 1)
+
+// uart is 115200 baud rate, 8 bits per word, no parrity and 1 stop bit
+// 115200 8N1
+void uart_init(void) {
+	// Set baud rate
+	UBRR0H	= (uint8_t)(UBRR_VALUE >> 8);
+	UBRR0L	= (uint8_t)(UBRR_VALUE);
+
+	UCSR0A |= _BV(U2X0);
+	// Enable transmitter
+	UCSR0B	= _BV(TXEN0) | _BV(RXEN0) | _BV(RXCIE0);
+
+	// Set frame format: 8 data bits, no parity, 1 stop bit
+	UCSR0C	= _BV(UCSZ01) | _BV(UCSZ00);
+
+	// Set TX (PD1) as output
+	DDRD   |= _BV(PD1);
+}
+
+void uart_tx(char data) {
+	// wait for transmit buffer to be empty
+	while (!(UCSR0A & _BV(UDRE0)))
+		;
+	// load data into transmit register
+	UDR0 = data;
+}
+
+char uart_rx(void) {
+	while (!(UCSR0A & _BV(RXC0)))
+		;
+	return UDR0;
+}
+
+void uart_sendstring(const char* str) {
+	if (!str)
+		return;
+	while (*str) {
+		uart_tx(*str);
+		str++;
+	}
+}

ex03/src/utils.c

@@ -0,0 +1,19 @@
+#include "utils.h"
+
+// this just burns cycles.
+// the volatile is important, it means that the cpu can't optimize any
+// read/writes for the value
+static inline void spin_loop(volatile uint16_t counts) {
+	while (counts)
+		counts--;
+}
+
+void delay_ms(uint16_t ms) {
+	while (ms) {
+		// this value was taken using a delay of 500ms, and just recording the led
+		// blinking. it seems to be high enough such that each loop of delay_loop
+		// takes 1ms :D
+		spin_loop((F_CPU) / 5000);
+		ms--;
+	}
+}