diff --git a/arduino/source/serial.c b/arduino/source/serial.c
deleted file mode 120000
index 3f397ae..0000000
--- a/arduino/source/serial.c
+++ /dev/null
@@ -1 +0,0 @@
-/home/mid-kid/Stuff/Workspace/bitsandpieces/atmega/serial.c
\ No newline at end of file
diff --git a/arduino/source/serial.c b/arduino/source/serial.c
new file mode 100644
index 0000000..7474512
--- /dev/null
+++ b/arduino/source/serial.c
@@ -0,0 +1,145 @@
+#include "serial.h"
+
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include <avr/io.h>
+#include <avr/interrupt.h>
+
+#include "utils.h"
+
+#define SERIAL_BUFFER_SIZE 0x40
+
+struct serial_buffer {
+    volatile unsigned char buffer[SERIAL_BUFFER_SIZE];
+    volatile unsigned head;
+    volatile unsigned tail;
+};
+
+static volatile struct serial_buffer serial_rx;
+static volatile struct serial_buffer serial_tx;
+
+__attribute__((always_inline))
+static inline int serial_buffer_isempty(volatile struct serial_buffer *buffer)
+{
+    return buffer->head == buffer->tail;
+}
+
+__attribute__((always_inline))
+static inline int serial_buffer_isfull(volatile struct serial_buffer *buffer)
+{
+    return ((buffer->head + 1) % SERIAL_BUFFER_SIZE) == buffer->tail;
+}
+
+__attribute__((always_inline))
+static inline void serial_buffer_put(volatile struct serial_buffer *buffer, char c)
+{
+    volatile unsigned head = buffer->head;
+    buffer->buffer[head++] = c;
+    buffer->head = head % SERIAL_BUFFER_SIZE;
+}
+
+__attribute__((always_inline))
+static inline char serial_buffer_get(volatile struct serial_buffer *buffer)
+{
+    volatile unsigned tail = buffer->tail;
+    char c = buffer->buffer[tail++];
+    buffer->tail = tail % SERIAL_BUFFER_SIZE;
+    return c;
+}
+
+static void serial_transmit(void)
+{
+    // Called when UDR0 is ready to receive new data
+
+    UDR0 = serial_buffer_get(&serial_tx);
+
+    // If we've sent everything, disable the interrupt
+    if (serial_buffer_isempty(&serial_tx)) cbi(UCSR0B, UDRIE0);
+}
+
+static void serial_receive(void)
+{
+    // Called when UDR0 contains new data
+
+    // Discard the byte if a parity error has occurred or the buffer is full
+    if (bit_is_set(UCSR0A, UPE0) || serial_buffer_isfull(&serial_rx)) {
+        UDR0;
+        return;
+    }
+
+    // There's not much we can do with a full buffer, unfortunately.
+    // Delaying the read will only cause it to be replaced with further data.
+
+    serial_buffer_put(&serial_rx, UDR0);
+}
+
+ISR(USART_UDRE_vect) { serial_transmit(); }
+ISR(USART_RX_vect) { serial_receive(); }
+
+__attribute__((always_inline))
+inline int serial_putchar_inline(const char c)
+{
+    // If the data register and buffer are empty, just send it straight away
+    if (bit_is_set(UCSR0A, UDRE0) && serial_buffer_isempty(&serial_tx)) {
+        UDR0 = c;
+        return 1;
+    }
+
+    // Make sure there's space in the buffer and put the character
+    while (serial_buffer_isfull(&serial_tx));
+    serial_buffer_put(&serial_tx, c);
+
+    // Enable the interrupt to transmit as soon as we can
+    sbi(UCSR0B, UDRIE0);
+
+    return 1;
+}
+
+int serial_putchar(const char c) { return serial_putchar_inline(c); }
+
+__attribute__((always_inline))
+inline int serial_getchar_inline(void)
+{
+    // Wait until there's something in the buffer
+    while (serial_buffer_isempty(&serial_rx));
+
+    // Read the next character
+    return serial_buffer_get(&serial_rx);
+}
+
+int serial_getchar(void) { return serial_getchar_inline(); }
+
+static int stdio_serial_putchar(const char c, __attribute__((unused)) FILE *stream)
+{ return serial_putchar(c); }
+static int stdio_serial_getchar(__attribute__((unused)) FILE *stream)
+{ return serial_getchar(); }
+static FILE serial = FDEV_SETUP_STREAM(stdio_serial_putchar, stdio_serial_getchar, _FDEV_SETUP_RW);
+
+unsigned serial_available(void)
+{
+    return ((unsigned)(SERIAL_BUFFER_SIZE + serial_rx.head - serial_rx.tail)) % SERIAL_BUFFER_SIZE;
+}
+
+void serial_drain(void)
+{
+    while (bit_is_set(UCSR0B, UDRIE0) || bit_is_set(UCSR0A, RXC0));
+}
+
+void serial_init_config(const unsigned long bauds, const uint8_t config)
+{
+    // Calculate UBRRn value as per the datasheet
+    uint16_t ubrr = F_CPU / 4 / 2 / bauds - 1;
+    UBRR0H = (ubrr >> 8) & 0xFF;
+    UBRR0L = ubrr & 0xFF;
+
+    // Configure the serial
+    UCSR0A = _BV(U2X0);  // Double speed
+    UCSR0B = _BV(RXEN0) | _BV(TXEN0) | _BV(RXCIE0);  // Enable it and the receive interrupt
+    UCSR0C = config;
+
+    // Setup stdio streams
+    stdout = stderr = stdin = &serial;
+}
+
+void serial_init(const unsigned long bauds) { serial_init_config(bauds, SERIAL_8N1); }
diff --git a/arduino/source/serial.h b/arduino/source/serial.h
deleted file mode 120000
index b56b899..0000000
--- a/arduino/source/serial.h
+++ /dev/null
@@ -1 +0,0 @@
-/home/mid-kid/Stuff/Workspace/bitsandpieces/atmega/serial.h
\ No newline at end of file
diff --git a/arduino/source/serial.h b/arduino/source/serial.h
new file mode 100644
index 0000000..e06f032
--- /dev/null
+++ b/arduino/source/serial.h
@@ -0,0 +1,37 @@
+#pragma once
+
+#include <stdint.h>
+
+#define SERIAL_5N1 0
+#define SERIAL_6N1 _BV(UCPHA0)
+#define SERIAL_7N1 _BV(UDORD0)
+#define SERIAL_8N1 _BV(UCPHA0) | _BV(UDORD0)
+#define SERIAL_5N2 _BV(USBS0)
+#define SERIAL_6N2 _BV(USBS0) | _BV(UCPHA0)
+#define SERIAL_7N2 _BV(USBS0) | _BV(UDORD0)
+#define SERIAL_8N2 _BV(USBS0) | _BV(UDORD0) | _BV(UCPHA0)
+#define SERIAL_5E1 _BV(UPM01)
+#define SERIAL_6E1 _BV(UPM01) | _BV(UCPHA0)
+#define SERIAL_7E1 _BV(UPM01) | _BV(UDORD0)
+#define SERIAL_8E1 _BV(UPM01) | _BV(UCPHA0) | _BV(UDORD0)
+#define SERIAL_5E2 _BV(UPM01) | _BV(USBS0)
+#define SERIAL_6E2 _BV(UPM01) | _BV(USBS0) | _BV(UCPHA0)
+#define SERIAL_7E2 _BV(UPM01) | _BV(USBS0) | _BV(UDORD0)
+#define SERIAL_8E2 _BV(UPM01) | _BV(USBS0) | _BV(UDORD0) | _BV(UCPHA0)
+#define SERIAL_5O1 _BV(UPM01) | _BV(UPM00)
+#define SERIAL_6O1 _BV(UPM01) | _BV(UPM00) | _BV(UCPHA0)
+#define SERIAL_7O1 _BV(UPM01) | _BV(UPM00) | _BV(UDORD0)
+#define SERIAL_8O1 _BV(UPM01) | _BV(UPM00) | _BV(UCPHA0) | _BV(UDORD0)
+#define SERIAL_5O2 _BV(UPM01) | _BV(UPM00) | _BV(USBS0)
+#define SERIAL_6O2 _BV(UPM01) | _BV(UPM00) | _BV(USBS0) | _BV(UCPHA0)
+#define SERIAL_7O2 _BV(UPM01) | _BV(UPM00) | _BV(USBS0) | _BV(UDORD0)
+#define SERIAL_8O2 _BV(UPM01) | _BV(UPM00) | _BV(USBS0) | _BV(UDORD0) | _BV(UCPHA0)
+
+int serial_putchar_inline(const char c);
+int serial_putchar(const char c);
+int serial_getchar_inline(void);
+int serial_getchar(void);
+unsigned serial_available(void);
+void serial_drain(void);
+void serial_init_config(const unsigned long bauds, const uint8_t config);
+void serial_init(const unsigned long bauds);
diff --git a/arduino/source/spi.c b/arduino/source/spi.c
deleted file mode 120000
index ff5bb1a..0000000
--- a/arduino/source/spi.c
+++ /dev/null
@@ -1 +0,0 @@
-/home/mid-kid/Stuff/Workspace/bitsandpieces/atmega/spi.c
\ No newline at end of file
diff --git a/arduino/source/spi.c b/arduino/source/spi.c
new file mode 100644
index 0000000..36ffaf9
--- /dev/null
+++ b/arduino/source/spi.c
@@ -0,0 +1,32 @@
+#include "spi.h"
+
+#include <stdint.h>
+#include <avr/io.h>
+
+#include "utils.h"
+#include "pins.h"
+
+void spi_init(const enum spi_divider divider)
+{
+    DDRB |= pin(PIN_SPI_SS) | pin(PIN_SPI_MOSI) | pin(PIN_SPI_SCK);  // Outputs
+    DDRB &= ~pin(PIN_SPI_MISO);  // Inputs
+    PORTB |= pin(PIN_SPI_MISO);  // Pull it up
+
+    // Configure SPI as master
+    SPCR = _BV(SPE) | _BV(MSTR) | (divider & 3);
+    SPSR = (divider & 4) >> 2;
+}
+
+void spi_off(void)
+{
+    SPCR = 0;
+    SPSR = 1;
+}
+
+uint8_t spi_transfer(const uint8_t data)
+{
+    SPDR = data;
+    __asm__ volatile ("nop");
+    while (!(SPSR & _BV(SPIF))) __asm__ volatile ("nop");
+    return SPDR;
+}
diff --git a/arduino/source/spi.h b/arduino/source/spi.h
deleted file mode 120000
index bfdf735..0000000
--- a/arduino/source/spi.h
+++ /dev/null
@@ -1 +0,0 @@
-/home/mid-kid/Stuff/Workspace/bitsandpieces/atmega/spi.h
\ No newline at end of file
diff --git a/arduino/source/spi.h b/arduino/source/spi.h
new file mode 100644
index 0000000..77fa438
--- /dev/null
+++ b/arduino/source/spi.h
@@ -0,0 +1,20 @@
+#pragma once
+
+#include <stdint.h>
+
+enum spi_divider {
+    SPI_DIV4,
+    SPI_DIV16,
+    SPI_DIV64,
+    SPI_DIV128,
+
+    // Double speed
+    SPI_DIV2,
+    SPI_DIV8,
+    SPI_DIV32,
+    SPI_DIV64_2
+};
+
+void spi_init(const enum spi_divider divider);
+void spi_off(void);
+uint8_t spi_transfer(const uint8_t data);
diff --git a/arduino/source/utils.h b/arduino/source/utils.h
deleted file mode 120000
index 7a808f2..0000000
--- a/arduino/source/utils.h
+++ /dev/null
@@ -1 +0,0 @@
-/home/mid-kid/Stuff/Workspace/bitsandpieces/atmega/utils.h
\ No newline at end of file
diff --git a/arduino/source/utils.h b/arduino/source/utils.h
new file mode 100644
index 0000000..f3420a4
--- /dev/null
+++ b/arduino/source/utils.h
@@ -0,0 +1,29 @@
+#pragma once
+
+#include <avr/io.h>
+
+#define cycles(us) (F_CPU * (long long)(us) / 1000000)
+
+#define cbi(sfr, bit) (sfr &= ~_BV(bit))
+#define sbi(sfr, bit) (sfr |= _BV(bit))
+
+// Stupid definitions for handling pins.
+
+#define _pin(port, pin) PORT ## port ## pin
+#define _port(port, pin) PORT ## port
+#define pin(pin) _BV(_pin(pin))
+#define port(pin) _port(pin)
+
+#define LOW 0
+#define HIGH 1
+#define OUTPUT 1
+#define INPUT 0
+
+#define _pinmode(port, pin, x) if (x) { sbi(DDR ## port, DD ## port ## pin); } else { cbi(DDR ## port, DD ## port ## pin); }
+#define pinmode(pin, x) _pinmode(pin, x)
+
+#define _writepin(port, pin, x) if (x) { sbi(PORT ## port, PORT ## port ## pin); } else { cbi(PORT ## port, PORT ## port ## pin); }
+#define writepin(pin, x) _writepin(pin, x)
+
+#define _readpin(port, pin) ((PIN ## port >> PORT ## port ## pin) & 1)
+#define readpin(pin) _readpin(pin)