diff --git a/nucleus/src/main.rs b/nucleus/src/main.rs
index cf4b4ae..de2e245 100644
--- a/nucleus/src/main.rs
+++ b/nucleus/src/main.rs
@@ -11,6 +11,7 @@
 #![no_main]
 #![feature(asm)]
 #![feature(global_asm)]
+#![feature(decl_macro)]
 #![feature(allocator_api)]
 #![feature(ptr_internals)]
 #![feature(format_args_nl)]
diff --git a/nucleus/src/platform/rpi3/gpio.rs b/nucleus/src/platform/rpi3/gpio.rs
new file mode 100644
index 0000000..7df64df
--- /dev/null
+++ b/nucleus/src/platform/rpi3/gpio.rs
@@ -0,0 +1,332 @@
+/*
+ * SPDX-License-Identifier: MIT OR BlueOak-1.0.0
+ * Copyright (c) 2018-2019 Andre Richter <andre.o.richter@gmail.com>
+ * Copyright (c) Berkus Decker <berkus+vesper@metta.systems>
+ * Original code distributed under MIT, additional changes are under BlueOak-1.0.0
+ */
+
+use {
+    super::BcmHost,
+    core::{marker::PhantomData, ops},
+    register::{
+        mmio::{ReadOnly, ReadWrite, WriteOnly},
+        register_bitfields, FieldValue,
+    },
+};
+
+// Descriptions taken from
+// https://github.com/raspberrypi/documentation/files/1888662/BCM2837-ARM-Peripherals.-.Revised.-.V2-1.pdf
+register_bitfields! {
+    u32,
+
+    /// GPIO Pull-up/down Clock Register 0
+    PUDCLK0 [
+        /// Pin 15
+        PUDCLK15 OFFSET(15) NUMBITS(1) [
+            NoEffect = 0,
+            AssertClock = 1
+        ],
+
+        /// Pin 14
+        PUDCLK14 OFFSET(14) NUMBITS(1) [
+            NoEffect = 0,
+            AssertClock = 1
+        ]
+    ]
+}
+
+/// Generates `pub enums` with no variants for each `ident` passed in.
+macro states($($name:ident),*) {
+$(pub enum $name {  })*
+}
+
+// Possible states for a GPIO pin.
+states! {
+    Uninitialized, Input, Output, Alt
+}
+
+/// A wrapper type that prevents reads or writes to its value.
+///
+/// This type implements no methods. It is meant to make the inner type
+/// inaccessible to prevent accidental reads or writes.
+#[repr(C)]
+pub struct Reserved<T>(T);
+
+/// The offsets for reach register.
+/// From https://wiki.osdev.org/Raspberry_Pi_Bare_Bones and
+/// https://github.com/raspberrypi/documentation/files/1888662/BCM2837-ARM-Peripherals.-.Revised.-.V2-1.pdf
+#[allow(non_snake_case)]
+#[repr(C)]
+pub struct RegisterBlock {
+    pub FSEL: [ReadWrite<u32>; 6], // 0x00-0x14 function select
+    __reserved_0: Reserved<u32>,   // 0x18
+    pub SET: [WriteOnly<u32>; 2],  // 0x1c-0x20 set output pin
+    __reserved_1: Reserved<u32>,   // 0x24
+    pub CLR: [WriteOnly<u32>; 2],  // 0x28-0x2c clear output pin
+    __reserved_2: Reserved<u32>,   // 0x30
+    pub LEV: [ReadOnly<u32>; 2],   // 0x34-0x38 get input pin level
+    __reserved_3: Reserved<u32>,   // 0x3C
+    pub EDS: [ReadWrite<u32>; 2],  // 0x40-0x44
+    __reserved_4: Reserved<u32>,   // 0x48
+    pub REN: [ReadWrite<u32>; 2],  // 0x4c-0x50
+    __reserved_5: Reserved<u32>,   // 0x54
+    pub FEN: [ReadWrite<u32>; 2],  // 0x58-0x5c
+    __reserved_6: Reserved<u32>,   // 0x60
+    pub HEN: [ReadWrite<u32>; 2],  // 0x64-0x68
+    __reserved_7: Reserved<u32>,   // 0x6c
+    pub LEN: [ReadWrite<u32>; 2],  // 0x70-0x74
+    __reserved_8: Reserved<u32>,   // 0x78
+    pub AREN: [ReadWrite<u32>; 2], // 0x7c-0x80
+    __reserved_9: Reserved<u32>,   // 0x84
+    pub AFEN: [ReadWrite<u32>; 2], // 0x88-0x8c
+    __reserved_10: Reserved<u32>,  // 0x90
+    pub PUD: ReadWrite<u32>,       // 0x94      pull up down
+    pub PUDCLK: [ReadWrite<u32, PUDCLK0::Register>; 2], // 0x98-0x9C -- @todo remove this register
+}
+
+/// Public interface to the GPIO MMIO area
+pub struct GPIO {
+    base_addr: usize,
+}
+
+/// Deref to RegisterBlock
+///
+/// Allows writing
+/// ```
+/// self.GPPUD.read()
+/// ```
+/// instead of something along the lines of
+/// ```
+/// unsafe { (*GPIO::ptr()).GPPUD.read() }
+/// ```
+impl ops::Deref for GPIO {
+    type Target = RegisterBlock;
+
+    fn deref(&self) -> &Self::Target {
+        unsafe { &*self.ptr() }
+    }
+}
+
+impl Default for GPIO {
+    fn default() -> GPIO {
+        // Default RPi3 GPIO base address
+        const GPIO_BASE: usize = BcmHost::get_peripheral_address() + 0x20_0000;
+        GPIO::new(GPIO_BASE)
+    }
+}
+
+impl GPIO {
+    pub fn new(base_addr: usize) -> GPIO {
+        GPIO { base_addr }
+    }
+
+    /// Returns a pointer to the register block
+    fn ptr(&self) -> *const RegisterBlock {
+        self.base_addr as *const _
+    }
+
+    pub fn get_pin(&self, pin: usize) -> Pin<Uninitialized> {
+        Pin::new(pin, self.base_addr)
+    }
+}
+
+/// An alternative GPIO function.
+#[repr(u8)]
+pub enum Function {
+    Input = 0b000,
+    Output = 0b001,
+    Alt0 = 0b100,
+    Alt1 = 0b101,
+    Alt2 = 0b110,
+    Alt3 = 0b111,
+    Alt4 = 0b011,
+    Alt5 = 0b010,
+}
+
+impl ::core::convert::From<Function> for u32 {
+    fn from(f: Function) -> Self {
+        f as u32
+    }
+}
+
+/// A GPIO pin in state `State`.
+///
+/// The `State` generic always corresponds to an un-instantiable type that is
+/// used solely to mark and track the state of a given GPIO pin. A `Pin`
+/// structure starts in the `Uninitialized` state and must be transitioned into
+/// one of `Input`, `Output`, or `Alt` via the `into_input`, `into_output`, and
+/// `into_alt` methods before it can be used.
+pub struct Pin<State> {
+    pin: usize,
+    base_addr: usize,
+    _state: PhantomData<State>,
+}
+
+impl<State> Pin<State> {
+    /// Transitions `self` to state `NewState`, consuming `self` and returning a new
+    /// `Pin` instance in state `NewState`. This method should _never_ be exposed to
+    /// the public!
+    #[inline(always)]
+    fn transition<NewState>(self) -> Pin<NewState> {
+        Pin {
+            pin: self.pin,
+            base_addr: self.base_addr,
+            _state: PhantomData,
+        }
+    }
+
+    /// Returns a pointer to the register block
+    #[inline(always)]
+    fn ptr(&self) -> *const RegisterBlock {
+        self.base_addr as *const _
+    }
+}
+
+/// Deref to Pin's Registers
+///
+/// Allows writing
+/// ```
+/// self.PUD.read()
+/// ```
+/// instead of something along the lines of
+/// ```
+/// unsafe { (*Pin::ptr()).PUD.read() }
+/// ```
+impl<State> ops::Deref for Pin<State> {
+    type Target = RegisterBlock;
+
+    fn deref(&self) -> &Self::Target {
+        unsafe { &*self.ptr() }
+    }
+}
+
+impl Pin<Uninitialized> {
+    /// Returns a new GPIO `Pin` structure for pin number `pin`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `pin` > `53`.
+    fn new(pin: usize, base_addr: usize) -> Pin<Uninitialized> {
+        if pin > 53 {
+            panic!("gpio::Pin::new(): pin {} exceeds maximum of 53", pin);
+        }
+
+        Pin {
+            base_addr,
+            pin,
+            _state: PhantomData,
+        }
+    }
+
+    /// Enables the alternative function `function` for `self`. Consumes self
+    /// and returns a `Pin` structure in the `Alt` state.
+    pub fn into_alt(self, function: Function) -> Pin<Alt> {
+        let bank = self.pin / 10;
+        let off = self.pin % 10;
+        self.FSEL[bank].modify(FieldValue::<u32, ()>::new(0b111, off * 3, function.into()));
+        self.transition()
+    }
+
+    /// Sets this pin to be an _output_ pin. Consumes self and returns a `Pin`
+    /// structure in the `Output` state.
+    pub fn into_output(self) -> Pin<Output> {
+        self.into_alt(Function::Output).transition()
+    }
+
+    /// Sets this pin to be an _input_ pin. Consumes self and returns a `Pin`
+    /// structure in the `Input` state.
+    pub fn into_input(self) -> Pin<Input> {
+        self.into_alt(Function::Input).transition()
+    }
+}
+
+impl Pin<Output> {
+    /// Sets (turns on) this pin.
+    pub fn set(&mut self) {
+        // Guarantees: pin number is between [0; 53] by construction.
+        let bank = self.pin / 32;
+        let shift = self.pin % 32;
+        self.SET[bank].set(1 << shift);
+    }
+
+    /// Clears (turns off) this pin.
+    pub fn clear(&mut self) {
+        // Guarantees: pin number is between [0; 53] by construction.
+        let bank = self.pin / 32;
+        let shift = self.pin % 32;
+        self.CLR[bank].set(1 << shift);
+    }
+}
+
+pub type Level = bool;
+
+impl Pin<Input> {
+    /// Reads the pin's value. Returns `true` if the level is high and `false`
+    /// if the level is low.
+    pub fn level(&self) -> Level {
+        // Guarantees: pin number is between [0; 53] by construction.
+        let bank = self.pin / 32;
+        let off = self.pin % 32;
+        self.LEV[bank].matches_all(FieldValue::<u32, ()>::new(1, off, 1))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test_case]
+    fn test_pin_transitions() {
+        let mut reg = [0u32; 40];
+        let gpio = GPIO::new(&mut reg as *mut _ as usize);
+
+        let _out = gpio.get_pin(1).into_output();
+        assert_eq!(reg[0], 0b001_000);
+        let _inp = gpio.get_pin(12).into_input();
+        assert_eq!(reg[1], 0b000_000_000);
+        let _alt = gpio.get_pin(35).into_alt(Function::Alt1);
+        assert_eq!(reg[3], 0b101_000_000_000_000_000);
+    }
+
+    #[test_case]
+    fn test_pin_outputs() {
+        let mut reg = [0u32; 40];
+        let gpio = GPIO::new(&mut reg as *mut _ as usize);
+
+        let pin = gpio.get_pin(1);
+        let mut out = pin.into_output();
+        out.set();
+        assert_eq!(reg[7], 0b10); // SET pin 1 = 1 << 1
+        out.clear();
+        assert_eq!(reg[10], 0b10); // CLR pin 1 = 1 << 1
+
+        let pin = gpio.get_pin(35);
+        let mut out = pin.into_output();
+        out.set();
+        assert_eq!(reg[8], 0b1000); // SET pin 35 = 1 << (35 - 32)
+        out.clear();
+        assert_eq!(reg[11], 0b1000); // CLR pin 35 = 1 << (35 - 32)
+    }
+
+    #[test_case]
+    fn test_pin_inputs() {
+        let mut reg = [0u32; 40];
+        let gpio = GPIO::new(&mut reg as *mut _ as usize);
+
+        let pin = gpio.get_pin(1);
+        let inp = pin.into_input();
+        assert_eq!(inp.level(), false);
+
+        reg[13] = 0b10;
+
+        assert_eq!(inp.level(), true);
+
+        let pin = gpio.get_pin(35);
+        let inp = pin.into_input();
+        assert_eq!(inp.level(), false);
+
+        reg[14] = 0b1000;
+
+        assert_eq!(inp.level(), true);
+    }
+}
diff --git a/nucleus/src/platform/rpi3/mod.rs b/nucleus/src/platform/rpi3/mod.rs
index 27369dc..cf8f75c 100644
--- a/nucleus/src/platform/rpi3/mod.rs
+++ b/nucleus/src/platform/rpi3/mod.rs
@@ -6,6 +6,7 @@
 #![allow(dead_code)]
 
 pub mod fb;
+pub mod gpio;
 pub mod mailbox;
 
 /// See BCM2835-ARM-Peripherals.pdf