diff --git a/firmware/Cargo.lock b/firmware/Cargo.lock
index 343e2c7..5b80994 100644
--- a/firmware/Cargo.lock
+++ b/firmware/Cargo.lock
@@ -120,6 +120,7 @@ dependencies = [
  "crc 1.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "embedded-hal 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "libm 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "nb 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "smoltcp 0.4.0 (git+https://github.com/m-labs/smoltcp?rev=cd893e6)",
  "tm4c129x 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "walkdir 1.0.7 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/firmware/Cargo.toml b/firmware/Cargo.toml
index c10efea..e903799 100644
--- a/firmware/Cargo.toml
+++ b/firmware/Cargo.toml
@@ -13,6 +13,7 @@ cortex-m-rt = "0.6"
 crc = { version = "1.7", default-features = false }
 tm4c129x = { version = "0.8", features = ["rt"] }
 embedded-hal = { version = "0.2", features = ["unproven"] }
+nb = "0.1"
 
 [dependencies.smoltcp]
 git = "https://github.com/m-labs/smoltcp"
diff --git a/firmware/src/board/mod.rs b/firmware/src/board/mod.rs
index 8fb7303..6c57e8e 100644
--- a/firmware/src/board/mod.rs
+++ b/firmware/src/board/mod.rs
@@ -2,6 +2,7 @@ use cortex_m;
 use tm4c129x;
 
 mod gpio;
+mod softspi;
 
 
 const LED1: u8 = 0x10; // PK4
diff --git a/firmware/src/board/softspi.rs b/firmware/src/board/softspi.rs
new file mode 100644
index 0000000..8d8e31a
--- /dev/null
+++ b/firmware/src/board/softspi.rs
@@ -0,0 +1,104 @@
+use embedded_hal::spi::FullDuplex;
+use embedded_hal::digital::v2::{InputPin, OutputPin};
+use nb::Error::WouldBlock;
+
+/// Bit-banged SPI
+pub struct SoftSpi<SCK, MOSI, MISO> {
+    sck: SCK,
+    mosi: MOSI,
+    miso: MISO,
+    state: State,
+    input: Option<u8>,
+}
+
+#[derive(PartialEq)]
+enum State {
+    Idle,
+    Transfer {
+        clock_phase: bool,
+        mask: u8,
+        output: u8,
+        input: u8,
+    },
+}
+
+impl<SCK: OutputPin, MOSI: OutputPin, MISO: InputPin> SoftSpi<SCK, MOSI, MISO> {
+    pub fn new(mut sck: SCK, mut mosi: MOSI, miso: MISO) -> Self {
+        let _ = sck.set_high();
+        let _ = mosi.set_low();
+        SoftSpi {
+            sck, mosi, miso,
+            state: State::Idle,
+            input: None,
+        }
+    }
+
+    /// Call this at twice the data rate
+    pub fn tick(&mut self) {
+        match self.state {
+            State::Idle => {}
+            State::Transfer { clock_phase: false,
+                              mask, output, input } => {
+                if output & mask != 0 {
+                    let _ = self.mosi.set_high();
+                } else {
+                    let _ = self.mosi.set_low();
+                }
+                let _ = self.sck.set_low();
+
+                self.state = State::Transfer {
+                    clock_phase: true,
+                    mask, output, input,
+                };
+            }
+            State::Transfer { clock_phase: true,
+                              mask, output, mut input } => {
+                let _ = self.sck.set_high();
+                if self.miso.is_high().unwrap_or(false) {
+                    input |= mask;
+                }
+
+                if mask != 1 {
+                    self.state = State::Transfer {
+                        clock_phase: false,
+                        mask: mask >> 1,
+                        output, input,
+                    };
+                } else {
+                    self.input = Some(input);
+                    self.state = State::Idle;
+                }
+            }
+        }
+    }
+}
+
+impl<SCK: OutputPin, MOSI: OutputPin, MISO: InputPin> FullDuplex<u8> for SoftSpi<SCK, MOSI, MISO> {
+    type Error = ();
+
+    fn read(&mut self) -> Result<u8, nb::Error<Self::Error>> {
+        match self.input.take() {
+            Some(input) =>
+                Ok(input),
+            None if self.state == State::Idle =>
+                Err(nb::Error::Other(())),
+            None =>
+                Err(WouldBlock),
+        }
+    }
+
+    fn send(&mut self, output: u8) -> Result<(), nb::Error<Self::Error>> {
+        match self.state {
+            State::Idle => {
+                self.state = State::Transfer {
+                    clock_phase: false,
+                    mask: 0x80,
+                    output,
+                    input: 0,
+                };
+                Ok(())
+            }
+            _ => Err(WouldBlock)
+        }
+    }
+}
diff --git a/firmware/src/main.rs b/firmware/src/main.rs
index 39c5b02..986756c 100644
--- a/firmware/src/main.rs
+++ b/firmware/src/main.rs
@@ -11,6 +11,7 @@ extern crate tm4c129x;
 extern crate smoltcp;
 extern crate crc;
 extern crate embedded_hal;
+extern crate nb;
 
 use core::cell::{Cell, RefCell};
 use core::fmt;