diff --git a/stackline/Cargo.toml b/stackline/Cargo.toml
old mode 100644
new mode 100755
diff --git a/stackline/src/context.rs b/stackline/src/context.rs
index ecc796f..43cb646 100644
--- a/stackline/src/context.rs
+++ b/stackline/src/context.rs
@@ -24,7 +24,7 @@ This type is most commonly found when implementing [`Tile::update`]:
 struct MyTile(u8);
 
 impl Tile for MyTile {
-    fn update<'b>(&'b mut self, ctx: UpdateContext<'b>) {
+    fn update<'b>(&'b mut self, mut ctx: UpdateContext<'b>) {
         // Counts the number of active neighbors
         let mut active_neighbors = 0;
 
@@ -45,7 +45,7 @@ impl Tile for MyTile {
         }
 
         self.0 = active_neighbors;
-        ctx.next_state(); // Go dormant
+        ctx.next_state(); // Become dormant
     }
 #
 #    fn transmit<'b>(&'b self, signal: std::rc::Rc<Signal>, ctx: TransmitContext<'b>) {}
diff --git a/stackline/src/pane.rs b/stackline/src/pane.rs
index 5b5ff07..c45f846 100644
--- a/stackline/src/pane.rs
+++ b/stackline/src/pane.rs
@@ -91,7 +91,8 @@ impl Pane {
         Some(())
     }
 
-    pub fn update_all(&mut self) {
+    /// Calls [`Pane::update`] on all non-empty, non-idle tiles
+    fn update_all(&mut self) {
         for y in 0..self.height.get() {
             for x in 0..self.width.get() {
                 if let Some((ctx, tile)) = UpdateContext::new(self, (x, y)) {
@@ -112,7 +113,8 @@ impl Pane {
         Some(())
     }
 
-    pub fn transmit_all(&mut self) {
+    /// Calls [`Pane::transmit`] on all tiles with a signal
+    fn transmit_all(&mut self) {
         // TODO: store a second buffer and perform swap reads
         for signal in std::mem::replace(&mut self.signals, vec![]) {
             if let Some(upgraded) = signal.upgrade() {
@@ -122,9 +124,24 @@ impl Pane {
         }
     }
 
+    /// Runs a single simulation step, which consists of:
+    /// - an update phase, which mutates the inner state of [active](State::Active)] cells by calling [`Tile::update`]
+    /// - a transmit phase, which mutates and moves signals between cells by calling [`Tile::transmit`]
+    pub fn step(&mut self) {
+        self.update_all();
+        self.transmit_all();
+    }
+
     /// Returns an iterator over the tiles and their coordinates
     #[inline]
     pub fn tiles<'b>(&'b self) -> impl Iterator<Item=(usize, usize, &'b FullTile)> + 'b {
         self.tiles.iter().enumerate().map(move |(i, v)| (i % self.width, i / self.width, v))
     }
+
+    /// Returns a mutable iterator over the tiles and their coordinates
+    #[inline]
+    pub fn tiles_mut<'b>(&'b mut self) -> impl Iterator<Item=(usize, usize, &'b mut FullTile)> + 'b {
+        let width = self.width;
+        self.tiles.iter_mut().enumerate().map(move |(i, v)| (i % width, i / width, v))
+    }
 }
diff --git a/stackline/src/tile/mod.rs b/stackline/src/tile/mod.rs
index 17ac71b..ecdc80e 100644
--- a/stackline/src/tile/mod.rs
+++ b/stackline/src/tile/mod.rs
@@ -130,6 +130,7 @@ pub trait Tile: DynClone + std::fmt::Debug {
 
     /// Should return true iff the tile accepts a signal travelling in `Direction`
     #[inline]
+    #[allow(unused_variables)]
     fn accepts_signal(&self, direction: Direction) -> bool {
         true
     }
diff --git a/stackline/src/tile/wire.rs b/stackline/src/tile/wire.rs
index 7e36a5d..6823f7b 100644
--- a/stackline/src/tile/wire.rs
+++ b/stackline/src/tile/wire.rs
@@ -42,6 +42,11 @@ impl Diode {
 
 impl Tile for Diode {
     fn transmit<'b>(&'b self, signal: Rc<Signal>, mut context: TransmitContext<'b>) {
+        // Block signals coming from where the diode is looking
+        if signal.direction().opposite() == self.0 {
+            return;
+        }
+
         if let Some(pos) = context.offset(self.0.into_offset()) {
             if context.accepts_signal(pos, self.0) {
                 context.send(pos, signal.clone_move(self.0).unwrap_or_else(|| unreachable!()));
@@ -66,49 +71,79 @@ mod test {
         // Test the signal going from left to right
         test_set_signal!(pane, (0, 0), Direction::Right);
 
-        pane.update_all();
-        pane.transmit_all();
+        pane.step();
 
         assert_signal!(pane, (1, 0));
         assert_no_signal!(pane, (0, 0));
         assert_no_signal!(pane, (2, 0));
         assert_no_signal!(pane, (1, 1));
 
-        pane.update_all();
-        pane.transmit_all();
+        pane.step();
 
         assert_signal!(pane, (2, 0));
         assert_signal!(pane, (1, 1));
         assert_no_signal!(pane, (0, 0));
         assert_no_signal!(pane, (1, 0));
 
-        pane.update_all();
-        pane.transmit_all();
+        pane.step();
         for (_, _, tile) in pane.tiles() {
             assert!(tile.signal().is_none());
         }
 
         // Let the simulation cool down
-        pane.update_all();
-        pane.update_all();
+        pane.step();
+        pane.step();
 
         // Test the signal going from right to left
         test_set_signal!(pane, (2, 0), Direction::Left);
 
-        pane.update_all();
-        pane.transmit_all();
+        pane.step();
 
         assert_signal!(pane, (1, 0));
         assert_no_signal!(pane, (0, 0));
         assert_no_signal!(pane, (2, 0));
         assert_no_signal!(pane, (1, 1));
 
-        pane.update_all();
-        pane.transmit_all();
+        pane.step();
 
         assert_signal!(pane, (0, 0));
         assert_signal!(pane, (1, 1));
         assert_no_signal!(pane, (2, 0));
         assert_no_signal!(pane, (1, 0));
     }
+
+    #[test]
+    fn test_diode_transmit() {
+        use crate::Direction::*;
+
+        let mut pane = test_tile_setup!(3, 2, [
+            Diode::new(Right), Diode::new(Right), Diode::new(Down),
+            (), Diode::new(Up), Diode::new(Left)
+        ]);
+
+        // Test the signal going from left to right
+        test_set_signal!(pane, (0, 0), Direction::Right);
+
+        pane.step();
+        assert_signal!(pane, (1, 0));
+        assert_no_signal!(pane, (0, 0));
+
+        let positions = [
+            (2, 0),
+            (2, 1),
+            (1, 1),
+            (1, 0)
+        ];
+
+        for &pos in positions.iter().cycle().take(16) {
+            pane.step();
+            assert_signal!(pane, pos);
+            for &pos2 in positions.iter() {
+                if pos == pos2 {
+                    continue
+                }
+                assert_no_signal!(pane, pos2);
+            }
+        }
+    }
 }