diff --git a/ex04/Makefile b/ex04/Makefile
new file mode 100644
index 0000000..db02f82
--- /dev/null
+++ b/ex04/Makefile
@@ -0,0 +1,61 @@
+# Makefile
+MCU=atmega328p
+F_CPU=16000000
+CC=avr-gcc
+OBJCOPY=avr-objcopy
+WFLAGS=-Wall -Wextra
+CFLAGS=--std=c99 -g -Os -mmcu=$(MCU) -ffunction-sections -fdata-sections
+CPPFLAGS=-DF_CPU=$(F_CPU) -MMD -Iinclude
+IFLAGS=
+LDFLAGS=-Wl,--gc-sections
+TARGET=main
+SERIAL=-P /dev/ttyUSB0 -b 115200
+
+SRC_DIR=src
+OBJ_DIR=build
+
+SRC_FILES=main.c utils.c uart.c rgb.c i2c.c aht20.c spi.c
+OBJ_FILES=$(patsubst %.c,%.o,$(SRC_FILES))
+DEP_FILES=$(patsubst %.c,%.d,$(SRC_FILES))
+
+SRC=$(addprefix $(SRC_DIR)/,$(SRC_FILES))
+OBJ=$(addprefix $(OBJ_DIR)/,$(OBJ_FILES))
+DEP=$(addprefix $(OBJ_DIR)/,$(DEP_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) $(CPPFLAGS) $(WFLAGS) $(CFLAGS) $(IFLAGS) -c $< -o $@
+
+$(ELF_FILE): $(OBJ)
+	$(CC) $(CFLAGS) $(LDFLAGS) $(OBJ) -o $@
+
+$(HEX_FILE): $(ELF_FILE)
+	$(OBJCOPY) -j .text -j .data -O ihex $< $@
+
+print:
+	@echo $(SRC)
+	@echo $(OBJ)
+	@echo $(ELF_FILE)
+	@echo $(HEX_FILE)
+
+-include $(DEP);
+
diff --git a/ex04/include/adc.h b/ex04/include/adc.h
new file mode 100644
index 0000000..6e32940
--- /dev/null
+++ b/ex04/include/adc.h
@@ -0,0 +1,74 @@
+#ifndef ADC_H
+#define ADC_H
+
+#include <avr/io.h>
+#include "mystd.h"
+
+typedef enum e_adc_ref {
+	ADC_AREF	  = 0,
+	ADC_AVCC	  = BV(REFS0),
+	ADC_INT		  = BV(REFS0) | BV(REFS1),
+
+	_ADC_REF_MASK = BV(REFS0) | BV(REFS1),
+} e_adc_ref;
+
+typedef enum e_adc_size {
+	ADC_10BIT	   = 0,
+	ADC_8BIT	   = BV(ADLAR),
+	_ADC_SIZE_MASK = BV(ADLAR),
+} e_adc_size;
+
+typedef enum e_adc_prescaler {
+	ADC_PRESCALER_2		= BV(ADPS0),
+	ADC_PRESCALER_4		= BV(ADPS1),
+	ADC_PRESCALER_8		= BV(ADPS1) | BV(ADPS0),
+	ADC_PRESCALER_16	= BV(ADPS2),
+	ADC_PRESCALER_32	= BV(ADPS2) | BV(ADPS0),
+	ADC_PRESCALER_64	= BV(ADPS2) | BV(ADPS1),
+	ADC_PRESCALER_128	= BV(ADPS2) | BV(ADPS1) | BV(ADPS0),
+
+	_ADC_PRESCALER_MASK = BV(ADPS2) | BV(ADPS1) | BV(ADPS0),
+
+} e_adc_prescaler;
+
+typedef enum e_adc_input {
+	ADC_ADC0		= 0,
+	ADC_ADC1		= BV(MUX0),
+	ADC_ADC2		= BV(MUX1),
+	ADC_ADC3		= BV(MUX0) | BV(MUX1),
+	ADC_ADC4		= BV(MUX2),
+	ADC_ADC5		= BV(MUX2) | BV(MUX0),
+	ADC_ADC6		= BV(MUX2) | BV(MUX1),
+	ADC_ADC7		= BV(MUX2) | BV(MUX1) | BV(MUX0),
+	ADC_TEMP		= BV(MUX3),
+	ADC_11V			= BV(MUX3) | BV(MUX2) | BV(MUX1),
+	ADC_0V			= BV(MUX3) | BV(MUX2) | BV(MUX1) | BV(MUX0),
+	_ADC_INPUT_MASK = BV(MUX0) | BV(MUX1) | BV(MUX2) | BV(MUX3),
+} e_adc_input;
+
+static inline uint8_t adc_read_pin(e_adc_input input) {
+	ADMUX	= (ADMUX & ~(_ADC_INPUT_MASK | _ADC_SIZE_MASK)) | input | BV(ADLAR);
+	ADCSRA |= BV(ADSC);
+
+	while (ADCSRA & BV(ADSC))
+		;
+	return ADCH;
+}
+
+static inline uint16_t adc_read_pin_10bit(e_adc_input input) {
+	ADMUX	= (ADMUX & ~(_ADC_SIZE_MASK | _ADC_INPUT_MASK)) | (input & _ADC_INPUT_MASK);
+	ADCSRA |= BV(ADSC);
+
+	while (ADCSRA & BV(ADSC))
+		;
+	return ADC;
+}
+
+static inline void adc_init(e_adc_ref v_ref, e_adc_prescaler prescaler) {
+	ADMUX  = (ADMUX & ~(_ADC_REF_MASK)) | v_ref;
+
+	ADCSRA = BV(ADEN) | (prescaler & _ADC_PRESCALER_MASK);
+
+	(void)adc_read_pin(0);
+}
+#endif /* ADC_H */
diff --git a/ex04/include/aht20.h b/ex04/include/aht20.h
new file mode 100644
index 0000000..4878a72
--- /dev/null
+++ b/ex04/include/aht20.h
@@ -0,0 +1,18 @@
+#ifndef AHT20_H
+#define AHT20_H
+
+#include <avr/io.h>
+
+typedef struct aht20_reading {
+		float temperature;
+		float humidity;
+} aht20_reading;
+
+aht20_reading aht20_read_measure(void);
+uint8_t		  aht20_status(void);
+void		  aht20_init(void);
+void		  aht20_print_status(uint8_t status);
+void		  aht20_trigger(void);
+#define AHT20 (0x38)
+
+#endif /* AHT20_H */
diff --git a/ex04/include/apa102.h b/ex04/include/apa102.h
new file mode 100644
index 0000000..584ec8a
--- /dev/null
+++ b/ex04/include/apa102.h
@@ -0,0 +1,40 @@
+#ifndef APA102_H
+#define APA102_H
+
+#include <avr/io.h>
+#include "mystd.h"
+#include "spi.h"
+
+typedef struct rgb {
+		uint8_t r;
+		uint8_t g;
+		uint8_t b;
+} rgb;
+
+static inline void apa102_set_colors(rgb col[], uint8_t brightness[], uint8_t length) {
+	// start frame
+	for (uint8_t i = 0; i < 4; i++)
+		spi_write(0x00);
+	// led data
+	for (uint8_t i = 0; i < length; i++) {
+		spi_write(0xE0 + (brightness[i] & 31));
+		spi_write(col[i].b);
+		spi_write(col[i].g);
+		spi_write(col[i].r);
+	}
+
+	// reset frame
+	for (uint8_t i = 0; i < 4; i++)
+		spi_write(0x00);
+
+	// End frame: 8+8*(leds >> 4) clock cycles
+	for (uint8_t i = 0; i < length; i += 16) {
+		spi_write(0x00);  // 8 more clock cycles
+	}
+}
+
+static inline void apa102_set_color(rgb col, uint8_t brightness) {
+	apa102_set_colors(&col, &brightness, 1);
+}
+
+#endif /* APA102_H */
diff --git a/ex04/include/eeprom.h b/ex04/include/eeprom.h
new file mode 100644
index 0000000..152344f
--- /dev/null
+++ b/ex04/include/eeprom.h
@@ -0,0 +1,70 @@
+#ifndef EEPROM_H
+#define EEPROM_H
+
+#include <avr/io.h>
+#include "interupt.h"
+#include "mystd.h"
+
+static inline void eeprom_wait(void) {
+	while (EECR & BV(EEPE))
+		;
+}
+static inline void eeprom_write_single_nocheck(uint16_t addr, uint8_t data) {
+	uint8_t sreg_save = SREG;
+	my_cli();
+
+	// wait until eeprom is good to go !
+	eeprom_wait();
+	while (SPMCSR & BV(SPMEN))
+		;
+
+	// setup the (addr, data) pair
+	EEAR  = addr;
+	EEDR  = data;
+
+	// we set the EEPROM master write bit
+	EECR  = (EECR & ~BV(EEPE)) | BV(EEMPE);
+	// within four cpu cycle, we need to set the EEPROM write bit, otherwise the writes doesnt work
+	// why 4 ? -> the master bit is reset after 4 cycles, and you need both to actually write
+	EECR |= BV(EEPE);
+
+	// this is the exact setup written in p32
+	// here the write should be done
+	SREG  = sreg_save;
+}
+
+static inline uint8_t eeprom_read_single(uint16_t addr) {
+	uint8_t sreg_save = SREG;
+	my_cli();
+	eeprom_wait();
+
+	EEAR  = addr;
+
+	EECR |= BV(EERE);
+
+	SREG  = sreg_save;
+	return EEDR;
+}
+
+// true on error
+static inline bool eeprom_write_single(uint16_t addr, uint8_t data) {
+	if (eeprom_read_single(addr) != data)
+		eeprom_write_single_nocheck(addr, data);
+
+	return (eeprom_read_single(addr) != data);
+}
+// true on error
+static inline bool eeprom_write(uint16_t addr, const uint8_t* data, uint16_t length) {
+	for (uint16_t i = 0; i < length; i++) {
+		if (eeprom_write_single(addr + i, data[i]))
+			return true;
+	}
+	return false;
+}
+
+static inline void eeprom_read(uint16_t addr, uint8_t* data, uint16_t length) {
+	for (uint16_t i = 0; i < length; i++)
+		data[i] = eeprom_read_single(addr + i);
+}
+
+#endif /* EEPROM_H */
diff --git a/ex04/include/i2c.h b/ex04/include/i2c.h
new file mode 100644
index 0000000..06b5054
--- /dev/null
+++ b/ex04/include/i2c.h
@@ -0,0 +1,57 @@
+#ifndef I2C_H
+#define I2C_H
+
+#include <avr/io.h>
+#include <util/twi.h>
+
+#define PCA9555_ADDR_OTHER 0b0100111
+#define PCA9555_ADDR_SELF  0b0100000
+
+#define REG_INPUT_PORT0	   0x00
+#define REG_INPUT_PORT1	   0x01
+
+#define REG_OUTPUT_PORT0   0x02
+#define REG_OUTPUT_PORT1   0x03
+
+#define REG_CONFIG_PORT0   0x06
+#define REG_CONFIG_PORT1   0x07
+
+#define I2C_CLOCK		   100000UL
+
+#define I2C_ADDR(ADDR, RW) ((ADDR) << 1 | (RW & 1))
+
+void	i2c_init(void);
+void	i2c_start(void);
+void	i2c_stop(void);
+void	i2c_write(uint8_t);
+uint8_t i2c_read_nack(void);
+uint8_t i2c_read_ack(void);
+uint8_t pca9555_read(uint8_t addr, uint8_t reg);
+
+void pca9555_write(uint8_t addr, uint8_t reg, uint8_t value);
+
+static inline void pca9555_set_output(uint8_t addr, uint8_t port, uint8_t mask) {
+	uint8_t cfg = pca9555_read(addr, port);
+	cfg		   &= ~mask;
+	pca9555_write(addr, port, cfg);
+}
+
+static inline void pca9555_set_low(uint8_t addr, uint8_t port, uint8_t mask) {
+	uint8_t out = pca9555_read(addr, port);
+	out		   &= ~mask;  // clear bit
+	pca9555_write(addr, port, out);
+}
+
+static inline void pca9555_set_high(uint8_t addr, uint8_t port, uint8_t mask) {
+	uint8_t out = pca9555_read(addr, port);
+	out		   |= mask;	 // set bit;
+	pca9555_write(addr, port, out);
+}
+
+static inline void pca9555_toggle(uint8_t addr, uint8_t port, uint8_t mask) {
+	uint8_t out = pca9555_read(addr, port);
+	out		   ^= mask;
+	pca9555_write(addr, port, out);
+}
+
+#endif /* I2C_H */
diff --git a/ex04/include/interupt.h b/ex04/include/interupt.h
new file mode 100644
index 0000000..7446788
--- /dev/null
+++ b/ex04/include/interupt.h
@@ -0,0 +1,15 @@
+#ifndef INTERUPT_H
+#define INTERUPT_H
+
+#include <avr/io.h>
+#include "mystd.h"
+
+static inline void my_sei(void) {
+	SREG |= BV(SREG_I);
+}
+
+static inline void my_cli(void) {
+	SREG &= ~BV(SREG_I);
+}
+
+#endif /* INTERUPT_H */
diff --git a/ex04/include/mystd.h b/ex04/include/mystd.h
new file mode 100644
index 0000000..113d592
--- /dev/null
+++ b/ex04/include/mystd.h
@@ -0,0 +1,20 @@
+#ifndef MYSTDINT_H
+#define MYSTDINT_H
+
+#include <avr/io.h>
+
+typedef unsigned char uint8_t;
+typedef signed char	  int8_t;
+
+typedef uint8_t bool;
+
+#define true	(1)
+#define false	(0)
+
+#define BV(bit) (1 << bit)
+
+#ifndef NULL
+#define NULL	((void*)0)
+#endif
+
+#endif /* MYSTDINT_H */
diff --git a/ex04/include/rgb.h b/ex04/include/rgb.h
new file mode 100644
index 0000000..d994365
--- /dev/null
+++ b/ex04/include/rgb.h
@@ -0,0 +1,9 @@
+#ifndef RGB_H
+#define RGB_H
+
+#include "mystd.h"
+
+void init_rgb(void);
+void set_rgb(uint8_t r, uint8_t g, uint8_t b);
+
+#endif /* RGB_H */
diff --git a/ex04/include/spi.h b/ex04/include/spi.h
new file mode 100644
index 0000000..e936d78
--- /dev/null
+++ b/ex04/include/spi.h
@@ -0,0 +1,16 @@
+#ifndef SPI_H
+#define SPI_H
+
+#define SPI_DDR DDRB
+#define CS		PINB2
+#define MOSI	PINB3
+#define MISO	PINB4
+#define SCK		PINB5
+
+#include "mystd.h"
+
+void	spi_init(void);
+void	spi_write(uint8_t data);
+uint8_t spi_read(void);
+
+#endif /* SPI_H */
diff --git a/ex04/include/timer0.h b/ex04/include/timer0.h
new file mode 100644
index 0000000..e7f6e92
--- /dev/null
+++ b/ex04/include/timer0.h
@@ -0,0 +1,168 @@
+#ifndef TIMER0_H
+#	define TIMER0_H
+
+#	include <avr/io.h>
+#	include "mystd.h"
+
+#	include "timer_global.h"
+
+static inline void t0_init_ctc_2(e_timer_prescaler prescaler) {
+	// Fast PWM (8-bit): WGM22:0 = 0b011
+	TCCR0A	= BV(WGM01);
+
+	// reset to zero -> timer off
+	TCCR0B &= ~(BV(CS02) | BV(CS01) | BV(CS00));
+	// set the correct prescaler
+	switch (prescaler) {
+		case (PRESCALER_1): {
+			TCCR0B |= (BV(CS00));
+			break;
+		}
+		case (PRESCALER_8): {
+			TCCR0B |= (BV(CS01));
+			break;
+		}
+		case (PRESCALER_64): {
+			TCCR0B |= (BV(CS01) | BV(CS00));
+			break;
+		}
+		case (PRESCALER_256): {
+			TCCR0B |= (BV(CS02));
+			break;
+		}
+		case (PRESCALER_1024): {
+			TCCR0B |= (BV(CS02) | BV(CS00));
+			break;
+		}
+		case (PRESCALER_OFF): {
+			break;
+		}
+	}
+}
+
+static inline void t0_init_fpwm_3(e_timer_prescaler prescaler) {
+	// Fast PWM (8-bit): WGM22:0 = 0b011
+	TCCR0A	= BV(WGM00) | BV(WGM01);
+
+	// reset to zero -> timer off
+	TCCR0B &= ~(BV(CS02) | BV(CS01) | BV(CS00));
+	// set the correct prescaler
+	switch (prescaler) {
+		case (PRESCALER_1): {
+			TCCR0B |= (BV(CS00));
+			break;
+		}
+		case (PRESCALER_8): {
+			TCCR0B |= (BV(CS01));
+			break;
+		}
+		case (PRESCALER_64): {
+			TCCR0B |= (BV(CS01) | BV(CS00));
+			break;
+		}
+		case (PRESCALER_256): {
+			TCCR0B |= (BV(CS02));
+			break;
+		}
+		case (PRESCALER_1024): {
+			TCCR0B |= (BV(CS02) | BV(CS00));
+			break;
+		}
+		case (PRESCALER_OFF): {
+			break;
+		}
+	}
+}
+
+static inline void t0_overflow_interrupt(bool enable) {
+	if (enable)
+		TIMSK0 |= BV(TOIE0);
+	else
+		TIMSK0 &= ~BV(TOIE0);
+}
+
+static inline void t0_interrupt(enum e_timer_output output, bool enable) {
+	if (output & TO_A) {
+		if (enable)
+			TIMSK0 |= BV(OCIE0A);
+		else
+			TIMSK0 &= ~BV(OCIE0A);
+	}
+	if (output & TO_B) {
+		if (enable)
+			TIMSK0 |= BV(OCIE0B);
+		else
+			TIMSK0 &= ~BV(OCIE0B);
+	}
+}
+
+static inline void t0_set_ocr(enum e_timer_output output, uint8_t value) {
+	if (output & TO_A)
+		OCR0A = value;
+	if (output & TO_B)
+		OCR0B = value;
+}
+
+static inline void t0_set_out_mode(enum e_timer_output output, enum e_timer_output_mode mode) {
+	if (output & TO_A) {
+		TCCR0A &= ~(BV(COM0A1) | BV(COM0A0));
+		switch (mode) {
+			case (TOM_00): {
+				break;
+			}
+			case (TOM_10): {
+				TCCR0A |= (BV(COM0A1));
+				break;
+			}
+			case (TOM_01): {
+				TCCR0A |= (BV(COM0A0));
+				break;
+			}
+			case (TOM_11): {
+				TCCR0A |= (BV(COM0A1) | BV(COM0A0));
+				break;
+			}
+		}
+	}
+	if (output & TO_B) {
+		TCCR0A &= ~(BV(COM0B1) | BV(COM0B0));
+		switch (mode) {
+			case (TOM_00): {
+				break;
+			}
+			case (TOM_10): {
+				TCCR0A |= (BV(COM0B1));
+				break;
+			}
+			case (TOM_01): {
+				TCCR0A |= (BV(COM0B0));
+				break;
+			}
+			case (TOM_11): {
+				TCCR0A |= (BV(COM0B1) | BV(COM0B0));
+				break;
+			}
+		}
+	}
+}
+
+// OC2B => RED   => PD3
+// OC0B => GREEN => PD5
+// OC0A => BLUE  => PD6
+
+#endif /* TIMER0_H */
+
+/*
+	// OC2B = PD3 → output
+	DDRD   |= BV(DDD3) | BV(DDD5) | BV(DDD6);
+
+	// Fast PWM (8-bit): WGM22:0 = 0b011
+	TCCR0A	= BV(WGM00) | BV(WGM01);
+	TCCR0A |= BV(COM0B1);
+
+	// 50% duty cycle
+	OCR0B	= 128;
+
+	// Start timer, prescaler = 64
+	TCCR0B	= BV(CS02);
+*/
diff --git a/ex04/include/timer1.h b/ex04/include/timer1.h
new file mode 100644
index 0000000..cf13fd2
--- /dev/null
+++ b/ex04/include/timer1.h
@@ -0,0 +1,159 @@
+#ifndef TIMER1_H
+#define TIMER1_H
+
+#include <avr/io.h>
+#include "mystd.h"
+
+#include "timer_global.h"
+
+static inline void t1_init_fpwm_14(e_timer_prescaler prescaler) {
+	// Fast PWM (8-bit): WGM22:0 = 0b011
+	TCCR1A = BV(WGM11);
+	TCCR1B = BV(WGM12) | BV(WGM13);
+
+	// set the correct prescaler
+	switch (prescaler) {
+		case (PRESCALER_1): {
+			TCCR1B |= (BV(CS10));
+			break;
+		}
+		case (PRESCALER_8): {
+			TCCR1B |= (BV(CS11));
+			break;
+		}
+		case (PRESCALER_64): {
+			TCCR1B |= (BV(CS11) | BV(CS10));
+			break;
+		}
+		case (PRESCALER_256): {
+			TCCR1B |= (BV(CS12));
+			break;
+		}
+		case (PRESCALER_1024): {
+			TCCR1B |= (BV(CS12) | BV(CS10));
+			break;
+		}
+		case (PRESCALER_OFF): {
+			break;
+		}
+	}
+}
+
+static inline void t1_init_ctc_4(e_timer_prescaler prescaler) {
+	// CTC mode 4
+	TCCR1A = 0;
+	TCCR1B = BV(WGM12);
+
+	// set the correct prescaler
+	switch (prescaler) {
+		case (PRESCALER_1): {
+			TCCR1B |= (BV(CS10));
+			break;
+		}
+		case (PRESCALER_8): {
+			TCCR1B |= (BV(CS11));
+			break;
+		}
+		case (PRESCALER_64): {
+			TCCR1B |= (BV(CS11) | BV(CS10));
+			break;
+		}
+		case (PRESCALER_256): {
+			TCCR1B |= (BV(CS12));
+			break;
+		}
+		case (PRESCALER_1024): {
+			TCCR1B |= (BV(CS12) | BV(CS10));
+			break;
+		}
+		case (PRESCALER_OFF): {
+			break;
+		}
+	}
+}
+
+static inline void t1_set_counter(uint16_t val) {
+	TCNT1 = val;
+}
+
+static inline void t1_set_icr1(uint16_t value) {
+	ICR1 = value;
+}
+
+static inline void t1_overflow_interrupt(bool enable) {
+	if (enable)
+		TIMSK1 |= BV(TOIE1);
+	else
+		TIMSK1 &= ~BV(TOIE1);
+}
+
+static inline void t1_interrupt(enum e_timer_output output, bool enable) {
+	if (output & TO_A) {
+		if (enable)
+			TIMSK1 |= BV(OCIE1A);
+		else
+			TIMSK1 &= ~BV(OCIE1A);
+	}
+	if (output & TO_B) {
+		if (enable)
+			TIMSK1 |= BV(OCIE1B);
+		else
+			TIMSK1 &= ~BV(OCIE1B);
+	}
+}
+
+static inline void t1_set_ocr(enum e_timer_output output, uint16_t value) {
+	if (output & TO_A)
+		OCR1A = value;
+	if (output & TO_B)
+		OCR1B = value;
+}
+
+static inline void t1_set_out_mode(enum e_timer_output output, enum e_timer_output_mode mode) {
+	if (output & TO_A) {
+		TCCR1A &= ~(BV(COM1A1) | BV(COM1A0));
+		switch (mode) {
+			case (TOM_00): {
+				break;
+			}
+			case (TOM_10): {
+				TCCR1A |= (BV(COM1A1));
+				break;
+			}
+			case (TOM_01): {
+				TCCR1A |= (BV(COM1A0));
+				break;
+			}
+			case (TOM_11): {
+				TCCR1A |= (BV(COM1A1) | BV(COM1A0));
+				break;
+			}
+		}
+	}
+	if (output & TO_B) {
+		TCCR1A &= ~(BV(COM1B1) | BV(COM1B0));
+		switch (mode) {
+			case (TOM_00): {
+				break;
+			}
+			case (TOM_10): {
+				TCCR1A |= (BV(COM1B1));
+				break;
+			}
+			case (TOM_01): {
+				TCCR1A |= (BV(COM1B0));
+				break;
+			}
+			case (TOM_11): {
+				TCCR1A |= (BV(COM1B1) | BV(COM1B0));
+				break;
+			}
+		}
+	}
+}
+
+// OC2B => RED   => PD3
+// OC0B => GREEN => PD5
+// OC0A => BLUE  => PD6
+
+#endif /* TIMER1_H */
diff --git a/ex04/include/timer2.h b/ex04/include/timer2.h
new file mode 100644
index 0000000..30bf320
--- /dev/null
+++ b/ex04/include/timer2.h
@@ -0,0 +1,134 @@
+#ifndef TIMER2_H
+#	define TIMER2_H
+
+#	include <avr/io.h>
+#	include "mystd.h"
+
+#	include "timer_global.h"
+
+static inline void t2_init_fpwm_3(e_timer_prescaler prescaler) {
+	// Fast PWM (8-bit): WGM22:0 = 0b011
+	TCCR2A	= BV(WGM20) | BV(WGM21);
+
+	// reset to zero -> timer off
+	TCCR2B &= ~(BV(CS22) | BV(CS21) | BV(CS20));
+	// set the correct prescaler
+	switch (prescaler) {
+		case (PRESCALER_1): {
+			TCCR2B |= (BV(CS20));
+			break;
+		}
+		case (PRESCALER_8): {
+			TCCR2B |= (BV(CS21));
+			break;
+		}
+		case (PRESCALER_64): {
+			TCCR2B |= (BV(CS21) | BV(CS20));
+			break;
+		}
+		case (PRESCALER_256): {
+			TCCR2B |= (BV(CS22));
+			break;
+		}
+		case (PRESCALER_1024): {
+			TCCR2B |= (BV(CS22) | BV(CS20));
+			break;
+		}
+		case (PRESCALER_OFF): {
+			break;
+		}
+	}
+}
+
+static inline void t2_overflow_interrupt(bool enable) {
+	if (enable)
+		TIMSK2 |= BV(TOIE2);
+	else
+		TIMSK2 &= ~BV(TOIE2);
+}
+
+static inline void t2_interrupt(enum e_timer_output output, bool enable) {
+	if (output & TO_A) {
+		if (enable)
+			TIMSK2 |= BV(OCIE2A);
+		else
+			TIMSK2 &= ~BV(OCIE2A);
+	}
+	if (output & TO_B) {
+		if (enable)
+			TIMSK2 |= BV(OCIE2B);
+		else
+			TIMSK2 &= ~BV(OCIE2B);
+	}
+}
+
+static inline void t2_set_ocr(enum e_timer_output output, uint8_t value) {
+	if (output & TO_A)
+		OCR2A = value;
+	if (output & TO_B)
+		OCR2B = value;
+}
+
+static inline void t2_set_out_mode(enum e_timer_output output, enum e_timer_output_mode mode) {
+	if (output & TO_A) {
+		TCCR2A &= ~(BV(COM2A1) | BV(COM2A0));
+		switch (mode) {
+			case (TOM_00): {
+				break;
+			}
+			case (TOM_10): {
+				TCCR2A |= (BV(COM2A1));
+				break;
+			}
+			case (TOM_01): {
+				TCCR2A |= (BV(COM2A0));
+				break;
+			}
+			case (TOM_11): {
+				TCCR2A |= (BV(COM2A1) | BV(COM2A0));
+				break;
+			}
+		}
+	}
+	if (output & TO_B) {
+		TCCR2A &= ~(BV(COM2B1) | BV(COM2B0));
+		switch (mode) {
+			case (TOM_00): {
+				break;
+			}
+			case (TOM_10): {
+				TCCR2A |= (BV(COM2B1));
+				break;
+			}
+			case (TOM_01): {
+				TCCR2A |= (BV(COM2B0));
+				break;
+			}
+			case (TOM_11): {
+				TCCR2A |= (BV(COM2B1) | BV(COM2B0));
+				break;
+			}
+		}
+	}
+}
+
+// OC2B => RED   => PD3
+// OC0B => GREEN => PD5
+// OC0A => BLUE  => PD6
+
+#endif /* TIMER0_H */
+
+/*
+	// OC2B = PD3 → output
+	DDRD   |= BV(DDD3) | BV(DDD5) | BV(DDD6);
+
+	// Fast PWM (8-bit): WGM22:0 = 0b011
+	TCCR2A	= BV(GM20) | BV(GM21);
+	TCCR2A |= BV(COM2B1);
+
+	// 50% duty cycle
+	OCR0B	= 128;
+
+	// Start timer, prescaler = 64
+	TCCR2B	= BV(CS22);
+*/
diff --git a/ex04/include/timer_global.h b/ex04/include/timer_global.h
new file mode 100644
index 0000000..7e1833a
--- /dev/null
+++ b/ex04/include/timer_global.h
@@ -0,0 +1,25 @@
+#ifndef TIMER_GLOBAL_H
+#define TIMER_GLOBAL_H
+
+typedef enum e_timer_prescaler {
+	PRESCALER_OFF  = 0,
+	PRESCALER_1	   = 1,
+	PRESCALER_8	   = 8,
+	PRESCALER_64   = 64,
+	PRESCALER_256  = 256,
+	PRESCALER_1024 = 1024,
+} e_timer_prescaler;
+
+typedef enum e_timer_output {
+	TO_A = (1 << 0),
+	TO_B = (1 << 1),
+} e_timer_output;
+
+typedef enum e_timer_output_mode {
+	TOM_00,
+	TOM_01,
+	TOM_10,
+	TOM_11,
+} e_timer_output_mode;
+
+#endif /* TIMER_GLOBAL_H */
diff --git a/ex04/include/uart.h b/ex04/include/uart.h
new file mode 100644
index 0000000..f775645
--- /dev/null
+++ b/ex04/include/uart.h
@@ -0,0 +1,29 @@
+#ifndef UART_H
+#define UART_H
+
+#include "mystd.h"
+
+void uart_init(void);
+
+void uart_tx(char data);
+void uart_sendstring(const char* str);
+
+void uart_send_u8(uint8_t val);
+void uart_send_u16(uint16_t val);
+void uart_send_u32(uint32_t val);
+
+
+void uart_send_i16(int16_t val);
+
+void uart_send_u8_hex(uint8_t val);
+void uart_send_u16_hex(uint16_t val);
+
+
+static inline void print_hex_value(char c)
+{
+	uart_send_u8_hex(c);
+}
+
+char uart_rx(void);
+
+#endif /* UART_H */
diff --git a/ex04/include/utils.h b/ex04/include/utils.h
new file mode 100644
index 0000000..a87a46c
--- /dev/null
+++ b/ex04/include/utils.h
@@ -0,0 +1,19 @@
+#ifndef UTILS_H
+#define UTILS_H
+
+#include "mystd.h"
+
+void delay_ms(uint16_t count);
+
+void ft_bzero(void* data, uint16_t size);
+
+uint8_t ft_stridx(const char* str, char chr);
+uint8_t ft_ftoa(float val, char* out, uint16_t precision);
+
+void* ft_memcpy(void* dest, void* src, uint16_t len);
+bool  ft_memcmp(void* s1, void* s2, uint16_t len);
+
+// return -1 on not hex digit
+uint8_t is_hex_digit(char chr);
+
+#endif /* UTILS_H */
diff --git a/ex04/src/aht20.c b/ex04/src/aht20.c
new file mode 100644
index 0000000..ebcb8a9
--- /dev/null
+++ b/ex04/src/aht20.c
@@ -0,0 +1,85 @@
+#include <avr/io.h>
+#include <util/delay.h>
+
+#include "aht20.h"
+#include "i2c.h"
+#include "uart.h"
+
+void aht20_print_status(uint8_t status) {
+	uart_sendstring("AHT20: ");
+	uart_sendstring((status & BV(3)) ? "Calibrated" : "Not Calibrated");
+	uart_sendstring(";");
+	uart_sendstring((status & BV(7)) ? "Busy" : "Not Busy");
+	uart_sendstring(";\r\n");
+}
+
+// https://datasheet4u.com/pdf/1551700/AHT20.pdf
+
+void aht20_init(void) {
+	// we need to wait a bit after the poweron of the AHT20 device
+	_delay_ms(40);
+
+	i2c_start();
+	i2c_write(I2C_ADDR(AHT20, TW_WRITE));
+	i2c_write(0xBE);
+	i2c_stop();
+
+	//_delay_ms(10);
+}
+
+void aht20_trigger(void) {
+	i2c_start();
+	i2c_write(I2C_ADDR(AHT20, TW_WRITE));
+	// trigger measurement command (7.4)
+	i2c_write(0xAC);
+	i2c_write(0x33);
+	i2c_write(0x00);
+	i2c_stop();
+}
+
+aht20_reading aht20_read_measure(void) {
+	uint8_t data[6];
+
+	i2c_start();
+	i2c_write(I2C_ADDR(AHT20, TW_READ));
+
+	for (uint8_t i = 0; i < 5; i++)
+		data[i] = i2c_read_ack();
+
+	data[5] = i2c_read_nack();
+	// we dont read the checksum
+
+	i2c_stop();
+
+	uint32_t raw_humi = 0;
+	uint32_t raw_temp = 0;
+
+	struct aht20_reading out;
+
+	raw_humi		= data[1];
+	raw_humi	  <<= 8;
+	raw_humi	   += data[2];
+	raw_humi	  <<= 4;
+	raw_humi	   += data[3] >> 4;
+
+	out.humidity	= (float)raw_humi / 1048576.0;
+
+	raw_temp		= data[3] & 0x0f;
+	raw_temp	  <<= 8;
+	raw_temp	   += data[4];
+	raw_temp	  <<= 8;
+	raw_temp	   += data[5];
+
+	out.temperature = (float)raw_temp / 1048576.0 * 200.0 - 50.0;
+
+	return out;
+}
+
+uint8_t aht20_status(void) {
+	i2c_start();
+	i2c_write(I2C_ADDR(AHT20, TW_READ));
+	uint8_t status = i2c_read_nack();
+	i2c_stop();
+
+	return status & (BV(7) | BV(3));
+}
diff --git a/ex04/src/i2c.c b/ex04/src/i2c.c
new file mode 100644
index 0000000..64a7e1e
--- /dev/null
+++ b/ex04/src/i2c.c
@@ -0,0 +1,74 @@
+#include "mystd.h"
+
+#include <avr/io.h>
+#include <util/twi.h>
+
+#include "i2c.h"
+
+void i2c_init(void) {
+	// clear the status registers
+	TWSR = 0x00;
+	// set the i2c clock speed
+	TWBR = ((F_CPU / I2C_CLOCK) - 16) / 2;
+}
+
+void i2c_start(void) {
+	//     CLR INT    | SET MASTER |  ENABLE  ;
+	TWCR = BV(TWINT) | BV(TWSTA) | BV(TWEN);
+
+	// wait until done
+	while (!(TWCR & BV(TWINT)))
+		;
+}
+
+void i2c_stop(void) {
+	//     CLR INT    | ENABLE    |  STOP     ;
+	TWCR = BV(TWINT) | BV(TWEN) | BV(TWSTO);
+}
+
+void i2c_write(uint8_t data) {
+	// set data to write
+	TWDR = data;
+	//     CLR INT    | ENABLE   ;
+	TWCR = BV(TWINT) | BV(TWEN);
+
+	// wait until done
+	while (!(TWCR & BV(TWINT)))
+		;
+}
+
+uint8_t i2c_read_ack(void) {
+	TWCR = BV(TWINT) | BV(TWEN) | BV(TWEA);
+	while (!(TWCR & BV(TWINT)))
+		;
+	return TWDR;
+}
+
+uint8_t i2c_read_nack(void) {
+	TWCR = BV(TWINT) | BV(TWEN);
+	while (!(TWCR & (1 << TWINT)))
+		;
+	return TWDR;
+}
+void pca9555_write(uint8_t addr, uint8_t reg, uint8_t value) {
+	i2c_start();
+	i2c_write((addr << 1) | TW_WRITE);	// write mode
+	i2c_write(reg);
+	i2c_write(value);
+	i2c_stop();
+}
+
+uint8_t pca9555_read(uint8_t addr, uint8_t reg) {
+	uint8_t val;
+
+	i2c_start();
+	i2c_write((addr << 1) | TW_WRITE);
+	i2c_write(reg);
+
+	i2c_start();  // repeated start
+	i2c_write((addr << 1) | TW_READ);
+	val = i2c_read_nack();
+
+	i2c_stop();
+	return val;
+}
diff --git a/ex04/src/main.c b/ex04/src/main.c
new file mode 100644
index 0000000..a3218c9
--- /dev/null
+++ b/ex04/src/main.c
@@ -0,0 +1,70 @@
+#include <avr/eeprom.h>
+#include <avr/io.h>
+#include <util/delay.h>
+
+#include "adc.h"
+#include "aht20.h"
+#include "apa102.h"
+#include "eeprom.h"
+#include "i2c.h"
+#include "mystd.h"
+#include "rgb.h"
+#include "spi.h"
+#include "uart.h"
+#include "utils.h"
+
+#define tabsize(tab) (sizeof(tab) / sizeof(tab[0]))
+
+static inline void set_col(rgb* rgb, uint8_t i, uint8_t val) {
+	if (i == 0)
+		rgb->r = val;
+	if (i == 1)
+		rgb->g = val;
+	if (i == 2)
+		rgb->b = val;
+}
+
+int main(void) {
+	init_rgb();
+	uart_init();
+	spi_init();
+	adc_init(ADC_AVCC, ADC_PRESCALER_128);
+
+	rgb colors[3] = {
+		{0x0, 0x00, 0x00},	//
+		{0x0, 0x00, 0x00},	//
+		{0x0, 0x00, 0x00},	//
+	};
+
+	uint8_t selected_led				= 0;
+	uint8_t selected_col				= 0;
+
+	uint8_t brightness[tabsize(colors)] = {};
+	for (uint8_t i = 0; i < tabsize(colors); i++)
+		brightness[i] = 31;
+
+	rgb display_col = {0, 0, 0};
+
+	apa102_set_color((rgb){0, 0, 0}, 31);
+	uint8_t prev = 0;
+	while (true) {
+		uint8_t data = adc_read_pin(ADC_ADC0);
+		display_col	 = (rgb){0, 0, 0};
+		set_col(&display_col, selected_col, data);
+		set_rgb(display_col.r, display_col.g, display_col.b);
+
+		uint8_t cur = PIND & (BV(PD2) | BV(PD4));
+		if ((prev & BV(PD2)) && !(cur & BV(PD2))) {
+			set_col(&colors[selected_led], selected_col, data);
+			selected_col += 1;
+			selected_col %= 3;
+		}
+		if ((prev & BV(PD4)) && !(cur & BV(PD4))) {
+			selected_led += 1;
+			selected_led %= 3;
+		}
+		prev = cur;
+		apa102_set_colors(colors, brightness, tabsize(colors));
+		_delay_ms(20);
+	}
+}
diff --git a/ex04/src/rgb.c b/ex04/src/rgb.c
new file mode 100644
index 0000000..6533dd3
--- /dev/null
+++ b/ex04/src/rgb.c
@@ -0,0 +1,45 @@
+#include <avr/io.h>
+#include "mystd.h"
+#include "timer0.h"
+#include "timer2.h"
+
+#define D5_R	 PD5
+#define D5_G	 PD6
+#define D5_B	 PD3
+
+#define RGB_MASK (_BV(D5_R) | _BV(D5_G) | _BV(D5_B))
+
+void init_rgb(void) {
+	t0_init_fpwm_3(PRESCALER_64);
+	t2_init_fpwm_3(PRESCALER_64);
+
+	t0_set_out_mode(TO_A | TO_B, TOM_00);
+	t2_set_out_mode(TO_B, TOM_00);
+	DDRD |= RGB_MASK;
+}
+
+void set_rgb(uint8_t r, uint8_t g, uint8_t b) {
+	if (r == 0x00) {
+		t0_set_out_mode(TO_B, TOM_00);
+		PORTD = (PORTD & ~_BV(D5_R));
+	} else {
+		t0_set_out_mode(TO_B, TOM_10);
+		t0_set_ocr(TO_B, r);
+	}
+
+	if (g == 0x00) {
+		t0_set_out_mode(TO_A, TOM_00);
+		PORTD = (PORTD & ~_BV(D5_G));
+	} else {
+		t0_set_out_mode(TO_A, TOM_10);
+		t0_set_ocr(TO_A, g);
+	}
+
+	if (b == 0x00) {
+		t2_set_out_mode(TO_B, TOM_00);
+		PORTD = (PORTD & ~_BV(D5_B));
+	} else {
+		t2_set_out_mode(TO_B, TOM_10);
+		t2_set_ocr(TO_B, b);
+	}
+}
diff --git a/ex04/src/spi.c b/ex04/src/spi.c
new file mode 100644
index 0000000..3c1a3ec
--- /dev/null
+++ b/ex04/src/spi.c
@@ -0,0 +1,33 @@
+#include <avr/io.h>
+
+#include "mystd.h"
+#include "spi.h"
+
+void spi_init(void) {
+	// set the correct pins as output
+	SPI_DDR |= BV(CS) | BV(MOSI) | BV(SCK);
+
+	// enable SPI, set as master, and clock to fosc/128
+	SPCR	 = BV(SPE) | BV(MSTR) | BV(SPR1) | BV(SPR0);
+}
+
+void spi_write(uint8_t data) {
+	// load data into register
+	SPDR = data;
+
+	// Wait for transmission complete
+	while (!(SPSR & BV(SPIF)))
+		;
+}
+
+uint8_t spi_read(void) {
+	// transmit dummy byte
+	SPDR = 0xFF;
+
+	// Wait for reception complete
+	while (!(SPSR & BV(SPIF)))
+		;
+
+	// return Data Register
+	return SPDR;
+}
diff --git a/ex04/src/uart.c b/ex04/src/uart.c
new file mode 100644
index 0000000..bb9f1b1
--- /dev/null
+++ b/ex04/src/uart.c
@@ -0,0 +1,139 @@
+#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);
+
+	// 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++;
+	}
+}
+void uart_send_u8(uint8_t val) {
+	if (val == 0)
+		return uart_tx('0');
+	char	buf[4]	= {0, 0, 0, 0};
+	uint8_t idx		= 0;
+	bool	print	= false;
+
+	uint8_t modulus = 100;
+	while (modulus) {
+		uint8_t digit = val / modulus;
+		if (print || digit != 0) {
+			print	   = true;
+			buf[idx++] = '0' + digit;
+		}
+		val		%= modulus;
+		modulus /= 10;
+	}
+
+	uart_sendstring(buf);
+}
+
+void uart_send_u16(uint16_t val) {
+	if (val == 0)
+		return uart_tx('0');
+	char	buf[6]	 = {0, 0, 0, 0, 0, 0};
+	uint8_t idx		 = 0;
+	bool	print	 = false;
+
+	uint16_t modulus = 10000;
+	while (modulus) {
+		uint8_t digit = val / modulus;
+		if (print || digit != 0) {
+			print	   = true;
+			buf[idx++] = '0' + digit;
+		}
+		val		%= modulus;
+		modulus /= 10;
+	}
+	uart_sendstring(buf);
+}
+
+void uart_send_i16(int16_t val) {
+	if (val == 0)
+		return uart_tx('0');
+	if (val == -32768)
+		return uart_sendstring("-32768");
+	if (val < 0) {
+		uart_tx('-');
+		val = -val;
+	}
+	uart_send_u16(val);
+}
+
+void uart_send_u32(uint32_t val) {
+	if (val == 0)
+		return uart_tx('0');
+	char	buf[11]	 = {};
+	uint8_t idx		 = 0;
+	bool	print	 = false;
+
+	uint32_t modulus = 1000000000;
+	while (modulus) {
+		uint8_t digit = val / modulus;
+		if (print || digit != 0) {
+			print	   = true;
+			buf[idx++] = '0' + digit;
+		}
+		val		%= modulus;
+		modulus /= 10;
+	}
+	uart_sendstring(buf);
+}
+
+void uart_send_u8_hex(uint8_t val) {
+	char buf[3] = {0, 0, 0};
+	buf[0]		= "0123456789abcdef"[(val >> 4) & 0x0F];
+	buf[1]		= "0123456789abcdef"[(val >> 0) & 0x0F];
+
+	uart_sendstring(buf);
+}
+
+void uart_send_u16_hex(uint16_t val) {
+	char buf[5] = {0, 0, 0, 0, 0};
+
+	buf[0]		= "0123456789abcdef"[(val >> 12) & 0x0F];
+	buf[1]		= "0123456789abcdef"[(val >> 8) & 0x0F];
+	buf[2]		= "0123456789abcdef"[(val >> 4) & 0x0F];
+	buf[3]		= "0123456789abcdef"[(val >> 0) & 0x0F];
+	uart_sendstring(buf);
+}
diff --git a/ex04/src/utils.c b/ex04/src/utils.c
new file mode 100644
index 0000000..1a9a782
--- /dev/null
+++ b/ex04/src/utils.c
@@ -0,0 +1,125 @@
+#include "utils.h"
+#include "mystd.h"
+#include "uart.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--;
+	}
+}
+
+void ft_bzero(void* data, uint16_t size) {
+	char* d = data;
+	while (size) {
+		*d = 0;
+		d++;
+		size--;
+	}
+}
+
+uint8_t ft_stridx(const char* str, char chr) {
+	if (!str)
+		return -1;
+	for (uint8_t i = 0; str[i]; i++) {
+		if (str[i] == chr)
+			return i;
+	}
+	return -1;
+}
+
+static float ft_pow(float base, float count) {
+	float out = 1;
+
+	while (count--)
+		out *= base;
+	return out;
+}
+
+// Reverses a string 'str' of length 'len'
+static void reverse(char* str, uint16_t len) {
+	uint16_t i = 0, j = len - 1, temp;
+	while (i < j) {
+		temp   = str[i];
+		str[i] = str[j];
+		str[j] = temp;
+		i++;
+		j--;
+	}
+}
+
+static uint16_t ft_itoa(uint32_t value, char* out, uint16_t width) {
+	uint16_t i = 0;
+	if (value == 0) {
+		while (i < width)
+			out[i++] = '0';
+		return i;
+	}
+	while (value) {
+		out[i++] = (value % 10) + '0';
+		value	 = value / 10;
+	}
+
+	// If number of digits required is more, then
+	// add 0s at the beginning
+	while (i < width)
+		out[i++] = '0';
+
+	// we need to reverse the data
+	reverse(out, i);
+	out[i] = 0;
+
+	return i;
+}
+// 0.3250351
+// Converts a floating-point/double number to a string.
+uint8_t ft_ftoa(float val, char* out, uint16_t precision) {
+	uint32_t ipart = (uint32_t)val;
+	float	 fpart = val - (float)ipart;
+
+	// convert integer part to string
+	uint8_t i	   = ft_itoa(ipart, out, 1);
+
+	if (precision != 0) {
+		out[i] = '.';
+		fpart  = fpart * ft_pow(10.f, precision);
+		i	  += ft_itoa((uint32_t)fpart, &out[i + 1], precision);
+	}
+	return i;
+}
+
+void* ft_memcpy(void* dest, void* src, uint16_t len) {
+	for (uint16_t i = 0; i < len; i++)
+		((uint8_t*)dest)[i] = ((uint8_t*)src)[i];
+	return dest;
+}
+
+bool ft_memcmp(void* s1, void* s2, uint16_t len) {
+	for (uint16_t i = 0; i < len; i++) {
+		if (((uint8_t*)s1)[i] != ((uint8_t*)s2)[i])
+			return false;
+	}
+	return true;
+}
+
+uint8_t is_hex_digit(char chr) {
+	uint8_t i;
+	if ((i = ft_stridx("0123456789", chr)) != 255)
+		return i;
+	if ((i = ft_stridx("abcdef", chr)) != 255)
+		return 10 + i;
+	if ((i = ft_stridx("ABCDEF", chr)) != 255)
+		return 10 + i;
+	return 255;
+}