feat(ex03): it works hehe

ex03/.clang-format

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+AccessModifierOffset: 0
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+  Enabled: true
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+  PadOperators: true
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+  AcrossEmptyLines: true
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+  AlignFunctionPointers: true
+  PadOperators: true
+AlignConsecutiveShortCaseStatements:
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+  AcrossEmptyLines: true
+  AcrossComments: true
+  AlignCaseArrows: true
+  AlignCaseColons: true
+ColumnLimit: 100
+NamespaceIndentation: All
+CommentPragmas: ""
+IncludeCategories:
+  - Regex: ^<.*\.h>
+    Priority: 1
+    SortPriority: 0
+    CaseSensitive: false
+  - Regex: ^<.*
+    Priority: 2
+    SortPriority: 0
+    CaseSensitive: false
+  - Regex: .*
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+    CaseSensitive: false
+IndentPPDirectives: AfterHash
+IndentWidth: 4
+TabWidth: 4
+UseTab: Always
+Language: Cpp
+IndentAccessModifiers: true

ex03/.gitignore

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+*.o
+*.hex
+*.bin
+*.elf
+build/
+/avr-libc
+compile_commands.json
+.cache/

ex03/Makefile

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+# Makefile
+MCU=atmega328p
+F_CPU=16000000
+CC=avr-gcc
+OBJCOPY=avr-objcopy
+CFLAGS=-std=c99 -Wall -Wextra -g -Os -mmcu=$(MCU) -DF_CPU=$(F_CPU) -Iinclude
+IFLAGS=
+TARGET=main
+SERIAL=-P /dev/ttyUSB0 -b 115200
+
+
+SRC_DIR=src
+OBJ_DIR=build
+
+SRC_FILES=main.c utils.c uart.c timer.c
+OBJ_FILES=$(patsubst %.c,%.o,$(SRC_FILES))
+
+SRC=$(addprefix $(SRC_DIR)/,$(SRC_FILES))
+OBJ=$(addprefix $(OBJ_DIR)/,$(OBJ_FILES))
+
+ELF_FILE=$(OBJ_DIR)/$(TARGET).elf
+HEX_FILE=$(OBJ_DIR)/$(TARGET).hex
+
+all: flash
+
+re: fclean all
+
+fclean: clean
+	rm -f $(HEX_FILE)
+	rm -f $(ELF_FILE)
+clean:
+	rm -rf $(OBJ_DIR)
+
+hex: $(HEX_FILE)
+
+flash: hex
+	avrdude -p $(MCU) -c arduino -U flash:w:$(HEX_FILE):i $(SERIAL) 
+
+
+$(OBJ_DIR)/%.o: $(SRC_DIR)/%.c 
+	@mkdir -p $(shell dirname $@)
+	$(CC) $(CFLAGS) $(IFLAGS) -c $< -o $@
+
+$(ELF_FILE): $(OBJ)
+	$(CC) $(CFLAGS) $(OBJ) -o $@
+
+$(HEX_FILE): $(ELF_FILE)
+	$(OBJCOPY) -j .text -j .data -O ihex $< $@
+
+print:
+	@echo $(SRC)
+	@echo $(OBJ)
+	@echo $(ELF_FILE)
+	@echo $(HEX_FILE)
+

ex03/include/mystd.h

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+#ifndef MYSTDINT_H
+#define MYSTDINT_H
+
+typedef unsigned int uint16_t;
+typedef signed int	 int16_t;
+
+typedef unsigned char uint8_t;
+typedef signed char	  int8_t;
+
+typedef uint8_t bool;
+
+#define true  (1)
+#define false (0)
+
+#endif /* MYSTDINT_H */

ex03/include/timer.h

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+#ifndef TIMER_H
+#define TIMER_H
+
+#include "mystd.h"
+
+void timer1_init(void);
+
+#endif /* TIMER_H */

ex03/include/uart.h

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+#ifndef UART_H
+#define UART_H
+
+#include "mystd.h"
+
+void uart_init(void);
+
+void uart_tx(char data);
+void uart_sendstring(const char* str);
+
+char uart_rx(void);
+
+#endif /* UART_H */

ex03/include/utils.h

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+#ifndef UTILS_H
+#define UTILS_H
+
+#include "mystd.h"
+
+void delay_ms(uint16_t count);
+
+#endif /* UTILS_H */

ex03/src/main.c

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+#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

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+
+#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

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+#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

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+#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--;
+	}
+}