diff --git a/Cargo.toml b/Cargo.toml
index 5a1a6d8..51034a4 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -12,3 +12,7 @@ description = """
 Reusable components for the Arduino Uno.
 """
 keywords = ["avr", "arduino", "uno"]
+
+[build-dependencies]
+avr-mcu = "0.2"
+
diff --git a/avr-atmega328p.json b/avr-atmega328p.json
new file mode 100644
index 0000000..951e1ef
--- /dev/null
+++ b/avr-atmega328p.json
@@ -0,0 +1,26 @@
+{
+  "llvm-target": "avr-unknown-unknown",
+  "cpu": "atmega328p",
+  "target-endian": "little",
+  "target-pointer-width": "16",
+  "os": "unknown",
+  "target-env": "",
+  "target-vendor": "unknown",
+  "arch": "avr",
+  "data-layout": "e-p:16:8-i8:8-i16:8-i32:8-i64:8-f32:8-f64:8-n8-a:8",
+
+  "executables": true,
+
+  "linker": "avr-gcc",
+  "linker-flavor": "gcc",
+  "pre-link-args": {
+    "gcc": ["-Os", "-mmcu=atmega328p"]
+  },
+  "exe-suffix": ".elf",
+  "post-link-args": {
+    "gcc": ["-Wl,--gc-sections"]
+  },
+
+  "no-default-libraries": false
+}
+
diff --git a/build.rs b/build.rs
new file mode 100644
index 0000000..1ccf925
--- /dev/null
+++ b/build.rs
@@ -0,0 +1,161 @@
+extern crate avr_mcu;
+
+use avr_mcu::*;
+use std::fs::{self, File};
+use std::io;
+use std::io::prelude::*;
+use std::path::{Path, PathBuf};
+
+fn cores_path() -> PathBuf {
+    Path::new(env!("CARGO_MANIFEST_DIR")).join("src").join("cores")
+}
+
+fn core_module_name(mcu: &Mcu) -> String {
+    mcu.device.name.to_lowercase().to_owned()
+}
+
+fn main() {
+    if !cores_path().exists() {
+        fs::create_dir_all(&cores_path()).expect("could not create cores directory");
+    }
+
+    let current_mcu = avr_mcu::current::mcu()
+        .expect("no target cpu specified");
+    generate_cores(&[current_mcu]).unwrap()
+}
+
+fn generate_cores(mcus: &[Mcu]) -> Result<(), io::Error> {
+    for mcu in mcus {
+        generate_core_module(mcu).expect("failed to generate mcu core");
+    }
+    generate_cores_mod_rs(mcus)
+}
+
+fn generate_core_module(mcu: &Mcu) -> Result<(), io::Error> {
+    let path = cores_path().join(format!("{}.rs", core_module_name(mcu)));
+    let mut file = File::create(&path)?;
+    write_core_module(mcu, &mut file)
+}
+
+fn generate_cores_mod_rs(mcus: &[Mcu]) -> Result<(), io::Error> {
+    let path = cores_path().join("mod.rs");
+    let mut w = File::create(&path)?;
+
+    writeln!(w, "//! Cores")?;
+    writeln!(w)?;
+    for mcu in mcus {
+        writeln!(w, "/// The {}.", mcu.device.name)?;
+        writeln!(w, "pub mod {};", core_module_name(mcu))?;
+    }
+    writeln!(w)
+}
+
+fn write_core_module(mcu: &Mcu, w: &mut Write) -> Result<(), io::Error> {
+    writeln!(w, "//! Core for {}.", mcu.device.name)?;
+    writeln!(w)?;
+    writeln!(w, "use {{HardwareSpi, Pin, Register}};")?;
+    writeln!(w)?;
+
+    gen::write_registers(mcu, w)?;
+    gen::write_pins(mcu, w)?;
+    gen::write_spi_modules(mcu, w)?;
+
+    writeln!(w)
+}
+
+mod gen {
+    use avr_mcu::*;
+    use std::io;
+    use std::io::prelude::*;
+
+    pub fn write_registers(mcu: &Mcu, w: &mut Write) -> Result<(), io::Error> {
+        for register in mcu.registers() {
+            let ty = if register.size == 1 { "u8" } else { "u16" };
+
+            // HACK: Skip, atmeg328p pack defines two of these.
+            if register.name == "GTCCR" { continue; }
+
+            writeln!(w, "pub struct {};", register.name)?;
+            writeln!(w, "impl Register<{}> for {} {{", ty, register.name)?;
+            writeln!(w, "    const ADDR: *mut {} = 0x{:x} as *mut {};", ty, register.offset, ty)?;
+            writeln!(w, "}}")?;
+        }
+
+        Ok(())
+    }
+
+    pub fn write_pins(mcu: &Mcu, w: &mut Write) -> Result<(), io::Error> {
+        if let Some(port) = mcu.peripheral("PORT") {
+            for instance in port.instances.iter() {
+                for signal in instance.signals.iter() {
+                    let idx = signal.index.expect("signal with no index");
+                    let struct_name = pin_name(instance, signal);
+
+                    let io_module = mcu.modules.iter().find(|m| m.name == "PORT")
+                        .expect("no port io module defined for this port");
+                    let register_group = io_module.register_groups.iter()
+                        .find(|rg| rg.name == instance.name)
+                        .expect("no register group defined for this port");
+
+                    writeln!(w, "pub struct {};", struct_name)?;
+                    writeln!(w)?;
+                    writeln!(w, "impl Pin for {} {{", struct_name)?;
+                    for reg in register_group.registers.iter() {
+                        let mut const_name = reg.name.clone();
+                        const_name.pop(); // Pop port character from register name (DDRB/PORTB/etc)..
+
+                        writeln!(w, "    /// {}.", reg.caption)?;
+                        writeln!(w, "    type {} = {};", const_name, reg.name)?;
+                    }
+                    writeln!(w, "    /// {}", signal.pad)?;
+                    writeln!(w, "    const MASK: u8 = 1<<{};", idx)?;
+                    writeln!(w, "}}")?;
+                    writeln!(w)?;
+                }
+            }
+        }
+        Ok(())
+    }
+
+    pub fn write_spi_modules(mcu: &Mcu, w: &mut Write) -> Result<(), io::Error> {
+        if let Some(module) = mcu.module("SPI") {
+            let peripheral = mcu.peripheral("SPI").expect("found SPI module but no peripheral");
+            let port_peripheral = mcu.port_peripheral();
+
+            writeln!(w, "pub struct Spi;")?;
+            writeln!(w)?;
+            writeln!(w, "impl HardwareSpi for Spi {{")?;
+
+            for spi_signal in peripheral.signals() {
+                let spi_signal_name = spi_signal.group.clone().expect("spi signal does not have group name");
+                let (port_instance, port_signal) = port_peripheral.instance_signal_with_pad(&spi_signal.pad)
+                    .expect("no port signal associated with the spi signal pad");
+                let pin_name = self::pin_name(port_instance, port_signal);
+
+                writeln!(w, "    type {} = {};", spi_signal_name, pin_name)?;
+            }
+
+            for reg in module.registers() {
+                let const_name = match &reg.caption[..] {
+                    "SPI Data Register" => "SPDR",
+                    "SPI Status Register" => "SPSR",
+                    "SPI Control Register" => "SPCR",
+                    _ => panic!("unknown SPI module register: '{}'", reg.caption),
+                };
+
+
+                writeln!(w, "    /// {}.", reg.caption)?;
+                writeln!(w, "    type {} = {};", const_name, reg.name)?;
+            }
+            writeln!(w, "}}")?;
+        }
+        Ok(())
+    }
+
+    /// Gets the name of a pin.
+    fn pin_name(instance: &Instance, signal: &Signal) -> String {
+        let idx = signal.index.expect("signal with no index");
+        format!("{}{}", instance.name, idx)
+    }
+}
+
diff --git a/build.sh b/build.sh
new file mode 100755
index 0000000..f780e29
--- /dev/null
+++ b/build.sh
@@ -0,0 +1,2 @@
+#! /bin/sh
+xargo build --target avr-atmega328p
diff --git a/src/cores/.gitignore b/src/cores/.gitignore
new file mode 100644
index 0000000..6f5f3d1
--- /dev/null
+++ b/src/cores/.gitignore
@@ -0,0 +1 @@
+*.rs
diff --git a/src/cores/.gitkeep b/src/cores/.gitkeep
new file mode 100644
index 0000000..e69de29
diff --git a/src/lib.rs b/src/lib.rs
index 08a1c3f..599ac9f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -6,12 +6,26 @@
 
 #![no_core]
 
-extern crate core;
+#![no_std]
+
+pub use self::reg::Register;
+pub use self::pin::Pin;
+pub use self::spi::HardwareSpi;
 
 pub mod prelude;
+pub mod serial;
 pub mod timer0;
 pub mod timer1;
-pub mod serial;
+pub mod cores;
+
+mod reg;
+mod pin;
+mod spi;
+
+pub enum DataDirection {
+    Input,
+    Output,
+}
 
 macro_rules! bit {
     (-, $pos:expr) => {};
diff --git a/src/pin.rs b/src/pin.rs
new file mode 100644
index 0000000..dfb76df
--- /dev/null
+++ b/src/pin.rs
@@ -0,0 +1,81 @@
+use {DataDirection, Register};
+
+/// An IO pin.
+pub trait Pin {
+    /// The associated data direction registerr.
+    type DDR: Register<u8>;
+    /// The associated port register.
+    type PORT: Register<u8>;
+    /// The associated pin register.
+    ///
+    /// Reads from the register will read input bits.
+    /// Writes to the register will toggle bits.
+    type PIN: Register<u8>;
+    /// The mask of the pin used for accessing registers.
+    const MASK: u8;
+
+    /// Sets the data direction of the pin.
+    #[inline(always)]
+    fn set_direction(direction: DataDirection) {
+        match direction {
+            DataDirection::Input => Self::set_input(),
+            DataDirection::Output => Self::set_output(),
+        }
+    }
+
+    /// Sets the pin up as an input.
+    #[inline(always)]
+    fn set_input() {
+        Self::DDR::unset(Self::MASK);
+    }
+
+    /// Sets the pin up as an output.
+    #[inline(always)]
+    fn set_output() {
+        Self::DDR::set(Self::MASK);
+    }
+
+    /// Set the pin to high.
+    ///
+    /// The pin must be configured as an output.
+    #[inline(always)]
+    fn set_high() {
+        Self::PORT::set(Self::MASK);
+    }
+
+    /// Set the pin to low.
+    ///
+    /// The pin must be configured as an output.
+    #[inline(always)]
+    fn set_low() {
+        Self::PORT::unset(Self::MASK);
+    }
+
+    /// Toggles the pin.
+    ///
+    /// The pin must be configured as an output.
+    #[inline(always)]
+    fn toggle() {
+        // FIXME: We can optimise this on post-2006 AVRs.
+        // http://www.avrfreaks.net/forum/toggle-state-output-pin
+        // set(Self::PIN, Self::MASK);
+        Self::PORT::toggle(Self::MASK);
+    }
+
+    /// Check if the pin is currently high.
+    ///
+    /// The pin must be configured as an input.
+    #[inline(always)]
+    fn is_high() -> bool {
+        Self::PIN::is_set(Self::MASK)
+    }
+
+    /// Checks if the pin is currently low.
+    ///
+    /// The pin must be configured as an input.
+    #[inline(always)]
+    fn is_low() -> bool {
+        Self::PIN::is_clear(Self::MASK)
+    }
+}
+
diff --git a/src/reg.rs b/src/reg.rs
new file mode 100644
index 0000000..194823f
--- /dev/null
+++ b/src/reg.rs
@@ -0,0 +1,95 @@
+use core::{cmp, convert, ops};
+
+pub trait RegVal : Copy + Clone +
+               ops::BitAnd<Output=Self> +
+               ops::BitAndAssign +
+               ops::BitOr<Output=Self> +
+               ops::BitOrAssign +
+               ops::BitXor<Output=Self> +
+               ops::BitXorAssign +
+               ops::Not<Output=Self> +
+               cmp::PartialEq + cmp::Eq +
+               cmp::PartialOrd + cmp::Ord +
+               convert::From<u8> {
+}
+
+/// A register.
+pub trait Register<T: RegVal> {
+    /// The address of the register.
+    const ADDR: *mut T;
+
+    /// Writes a value to the register.
+    #[inline(always)]
+    fn write(value: T) {
+        unsafe {
+            *Self::ADDR = value;
+        }
+    }
+
+    /// Reads the value of the register.
+    #[inline(always)]
+    fn read() -> T {
+        unsafe { *Self::ADDR }
+    }
+
+    /// Sets a bitmask in a register.
+    #[inline(always)]
+    fn set(mask: T) {
+        unsafe {
+            *Self::ADDR |= mask;
+        }
+    }
+
+    /// Clears a bitmask from a register.
+    #[inline(always)]
+    fn unset(mask: T) {
+        unsafe {
+            *Self::ADDR &= !mask;
+        }
+    }
+
+    /// Toggles a mask in the register.
+    #[inline(always)]
+    fn toggle(mask: T) {
+        unsafe {
+            *Self::ADDR ^= mask;
+        }
+    }
+
+    /// Checks if a mask is set in the register.
+    #[inline(always)]
+    fn is_set(mask: T) -> bool {
+        unsafe {
+            (*Self::ADDR & mask) == mask
+        }
+    }
+
+    /// Checks if a mask is clear in the register.
+    #[inline(always)]
+    fn is_clear(mask: T) -> bool {
+        unsafe {
+            (*Self::ADDR & mask) == T::from(0)
+        }
+    }
+
+    /// Waits until some condition is true of the register.
+    #[inline(always)]
+    fn wait_until<F>(mut f: F)
+        where F: FnMut() -> bool {
+        loop {
+            if f() {
+                break;
+            }
+        }
+    }
+
+    /// Waits until a mask is set.
+    #[inline(always)]
+    fn wait_until_set(mask: T) {
+        Self::wait_until(|| Self::is_set(mask))
+    }
+}
+
+impl RegVal for u8 { }
+impl RegVal for u16 { }
+
diff --git a/src/spi.rs b/src/spi.rs
new file mode 100644
index 0000000..71d5892
--- /dev/null
+++ b/src/spi.rs
@@ -0,0 +1,166 @@
+use {Register, Pin};
+
+
+/// An SPI module.
+///
+/// Information at
+/// http://maxembedded.com/2013/11/the-spi-of-the-avr/
+pub trait HardwareSpi {
+    /// Master-in slave-out pin.
+    type MISO: Pin;
+    /// Master-out slave-in pin.
+    type MOSI: Pin;
+    /// Serial clock pin.
+    type SCK: Pin;
+    /// Slave-select pin.
+    type SS: Pin;
+
+    /// The SPI control register.
+    type SPCR: Register<u8>;
+    /// The SPI status register.
+    type SPSR: Register<u8>;
+    /// The SPI data register.
+    type SPDR: Register<u8>;
+
+    /// Sets up the SPI as a master.
+    fn setup_master() {
+        // Setup DDR registers.
+        Self::MISO::set_input();
+        Self::MOSI::set_output();
+        Self::SCK::set_output();
+        Self::SS::set_input();
+
+        Self::set_master();
+        Self::enable_interrupt();
+        Self::enable();
+    }
+
+    /// Sets up the SPI as a slave.
+    fn setup_slave() {
+        // Setup DDR registers.
+        Self::MISO::set_output();
+        Self::MOSI::set_input();
+        Self::SCK::set_input();
+        Self::SS::set_input();
+
+        Self::set_slave();
+        Self::enable();
+    }
+
+    /// Enables interrupts for the spi module.
+    #[inline(always)]
+    fn enable_interrupt() {
+        Self::SPCR::set(spcr::INTERRUPT_ENABLE);
+    }
+
+    /// Disables interrupts for the spi module.
+    #[inline(always)]
+    fn disable_interrupt() {
+        Self::SPCR::unset(spcr::INTERRUPT_ENABLE);
+    }
+
+    /// Enables the SPI.
+    #[inline(always)]
+    fn enable() {
+        Self::SPCR::set(spcr::ENABLE);
+    }
+
+    /// Disables the SPI.
+    #[inline(always)]
+    fn disable() {
+        Self::SPCR::unset(spcr::ENABLE);
+    }
+
+    /// Enables least-significant-bit first.
+    #[inline(always)]
+    fn set_lsb() {
+        Self::SPCR::set(spcr::DATA_ORDER_LSB);
+    }
+
+    /// Enables most-significant-bit first.
+    #[inline(always)]
+    fn set_msb() {
+        Self::SPCR::unset(spcr::DATA_ORDER_LSB);
+    }
+
+    /// Enables master mode.
+    #[inline(always)]
+    fn set_master() {
+        Self::SPCR::set(spcr::MASTER);
+    }
+
+    /// Enables slave mode.
+    #[inline(always)]
+    fn set_slave() {
+        Self::SPCR::unset(spcr::MASTER);
+    }
+
+    /// Enables double speed mode.
+    #[inline(always)]
+    fn enable_double_speed() {
+        Self::SPSR::set(spsr::SPI2X);
+    }
+
+    /// Disables double speed mode.
+    #[inline(always)]
+    fn disable_double_speed() {
+        Self::SPSR::unset(spsr::SPI2X);
+    }
+
+    /// Checks if there is a write collision.
+    #[inline(always)]
+    fn is_write_collision() -> bool {
+        Self::SPSR::is_set(spsr::WCOL)
+    }
+
+    /// Sends a byte through the serial.
+    #[inline(always)]
+    fn send_byte(byte: u8) {
+        Self::SPDR::write(byte);
+        Self::SPSR::wait_until_set(spsr::SPIF);
+    }
+
+    /// Reads a byte from the serial.
+    #[inline(always)]
+    fn receive_byte() -> u8 {
+        Self::SPSR::wait_until_set(spsr::SPIF);
+        Self::SPDR::read()
+    }
+
+    /// Sends and receives a byte.
+    #[inline(always)]
+    fn send_receive(byte: u8) -> u8 {
+        Self::SPDR::write(byte);
+        Self::SPSR::wait_until_set(spsr::SPIF);
+        Self::SPDR::read()
+    }
+}
+
+/// Constants for the control register.
+#[allow(dead_code)]
+mod spcr {
+    pub const INTERRUPT_ENABLE: u8 = 1<<7;
+    pub const ENABLE: u8 = 1<<6;
+    pub const DATA_ORDER_LSB: u8 = 1<<5;
+    pub const MASTER: u8 = 1<<4;
+    /// Clock polarity.
+    pub const CPOL: u8 = 1<<3;
+    /// Clock phase.
+    pub const CPHA: u8 = 1<<2;
+    /// Clock rate select 1.
+    pub const SPR1: u8 = 1<<1;
+    /// Clock rate select 2.
+    pub const SPR0: u8 = 1<<0;
+}
+
+/// Constants for the status register.
+#[allow(dead_code)]
+mod spsr {
+    /// SPI interrupt flag.
+    pub const SPIF: u8 = 1<<7;
+    /// Write collision flag.
+    pub const WCOL: u8 = 1<<6;
+    /// SPI double speed mode.
+    pub const SPI2X: u8 = 1<<0;
+}
+