diff --git a/crates/coremem/src/diagnostics.rs b/crates/coremem/src/diagnostics.rs
new file mode 100644
index 0000000..021adec
--- /dev/null
+++ b/crates/coremem/src/diagnostics.rs
@@ -0,0 +1,92 @@
+use std::sync::{Arc, Mutex};
+use std::time::{Duration, Instant};
+
+pub struct Diagnostics {
+    frames_completed: u64,
+    time_spent_stepping: Duration,
+    time_spent_on_stimuli: Duration,
+    time_spent_prepping_render: Duration,
+    time_spent_blocked_on_render: Duration,
+    time_spent_rendering: Duration,
+    start_time: Instant,
+}
+
+#[derive(Clone)]
+pub struct SyncDiagnostics(Arc<Mutex<Diagnostics>>);
+
+impl Diagnostics {
+    pub fn new() -> Self {
+        Self {
+            frames_completed: 0,
+            time_spent_stepping: Default::default(),
+            time_spent_on_stimuli: Default::default(),
+            time_spent_prepping_render: Default::default(),
+            time_spent_blocked_on_render: Default::default(),
+            time_spent_rendering: Default::default(),
+            start_time: Instant::now(),
+        }
+    }
+
+    pub fn format(&self) -> String {
+        let step_time = self.time_spent_stepping.as_secs_f64();
+        let stim_time = self.time_spent_on_stimuli.as_secs_f64();
+        let render_time = self.time_spent_rendering.as_secs_f64();
+        let render_prep_time = self.time_spent_prepping_render.as_secs_f64();
+        let block_time = self.time_spent_blocked_on_render.as_secs_f64();
+        let overall_time = self.start_time.elapsed().as_secs_f64();
+        let fps = (self.frames_completed as f64) / overall_time;
+        format!("fps: {:6.2} (sim: {:.1}s, stim: {:.1}s, [render: {:.1}s], blocked: {:.1}s, render_prep: {:.1}s, other: {:.1}s)",
+            fps,
+            step_time,
+            stim_time,
+            render_time,
+            block_time,
+            render_prep_time,
+            overall_time - step_time - stim_time - block_time - render_prep_time,
+        )
+    }
+}
+
+impl SyncDiagnostics {
+    pub fn new() -> Self {
+        Self(Arc::new(Mutex::new(Diagnostics::new())))
+    }
+    pub fn format(&self) -> String {
+        self.0.lock().unwrap().format()
+    }
+    /// measure the duration of some arbitrary chunk of code.
+    /// used internally.
+    pub fn measure<F: FnOnce()>(f: F) -> Duration {
+        let start = Instant::now();
+        f();
+        start.elapsed()
+    }
+
+    /// record the duration of the sim step operation.
+    pub fn instrument_step<F: FnOnce()>(&self, frames: u64, f: F) {
+        let elapsed = Self::measure(f);
+        let mut me = self.0.lock().unwrap();
+        me.time_spent_stepping += elapsed;
+        me.frames_completed += frames as u64;
+    }
+
+    /// record the duration spent preparing for render (i.e. cloning stuff and moving it into a
+    /// render pool).
+    pub fn instrument_render_prep<F: FnOnce()>(&self, f: F) {
+        let elapsed = Self::measure(f);
+        self.0.lock().unwrap().time_spent_prepping_render += elapsed;
+    }
+
+    /// record the duration actually spent doing CPU render work
+    pub fn instrument_render_cpu_side<F: FnOnce()>(&self, f: F) {
+        let elapsed = Self::measure(f);
+        self.0.lock().unwrap().time_spent_rendering += elapsed;
+    }
+
+    /// record the duration spent blocking the simulation because the render queue is full.
+    pub fn instrument_render_blocked<F: FnOnce()>(&self, f: F) {
+        let elapsed = Self::measure(f);
+        self.0.lock().unwrap().time_spent_blocked_on_render += elapsed;
+    }
+}
+
diff --git a/crates/coremem/src/driver.rs b/crates/coremem/src/driver.rs
index 022f53c..d01990c 100644
--- a/crates/coremem/src/driver.rs
+++ b/crates/coremem/src/driver.rs
@@ -1,3 +1,4 @@
+use crate::diagnostics::SyncDiagnostics;
 use crate::geom::{Coord, Index, Meters, Region};
 use crate::mat;
 use crate::meas::{self, AbstractMeasurement};
@@ -10,9 +11,9 @@ use crate::stim::{self, AbstractStimulus};
 use log::{info, trace};
 use serde::{Deserialize, Serialize};
 use std::path::PathBuf;
-use std::sync::{Arc, Mutex};
+use std::sync::Arc;
 use std::sync::mpsc::{sync_channel, SyncSender, Receiver};
-use std::time::{Duration, Instant};
+use std::time::Instant;
 use threadpool::ThreadPool;
 
 pub struct Driver<S> {
@@ -29,95 +30,6 @@ pub struct Driver<S> {
     last_diag_time: Instant,
 }
 
-struct Diagnostics {
-    frames_completed: u64,
-    time_spent_stepping: Duration,
-    time_spent_on_stimuli: Duration,
-    time_spent_prepping_render: Duration,
-    time_spent_blocked_on_render: Duration,
-    time_spent_rendering: Duration,
-    start_time: Instant,
-}
-
-#[derive(Clone)]
-struct SyncDiagnostics(Arc<Mutex<Diagnostics>>);
-
-impl Diagnostics {
-    fn new() -> Self {
-        Self {
-            frames_completed: 0,
-            time_spent_stepping: Default::default(),
-            time_spent_on_stimuli: Default::default(),
-            time_spent_prepping_render: Default::default(),
-            time_spent_blocked_on_render: Default::default(),
-            time_spent_rendering: Default::default(),
-            start_time: Instant::now(),
-        }
-    }
-
-    fn format(&self) -> String {
-        let step_time = self.time_spent_stepping.as_secs_f64();
-        let stim_time = self.time_spent_on_stimuli.as_secs_f64();
-        let render_time = self.time_spent_rendering.as_secs_f64();
-        let render_prep_time = self.time_spent_prepping_render.as_secs_f64();
-        let block_time = self.time_spent_blocked_on_render.as_secs_f64();
-        let overall_time = self.start_time.elapsed().as_secs_f64();
-        let fps = (self.frames_completed as f64) / overall_time;
-        format!("fps: {:6.2} (sim: {:.1}s, stim: {:.1}s, [render: {:.1}s], blocked: {:.1}s, render_prep: {:.1}s, other: {:.1}s)",
-            fps,
-            step_time,
-            stim_time,
-            render_time,
-            block_time,
-            render_prep_time,
-            overall_time - step_time - stim_time - block_time - render_prep_time,
-        )
-    }
-}
-
-impl SyncDiagnostics {
-    fn new() -> Self {
-        Self(Arc::new(Mutex::new(Diagnostics::new())))
-    }
-    fn format(&self) -> String {
-        self.0.lock().unwrap().format()
-    }
-    /// measure the duration of some arbitrary chunk of code.
-    /// used internally.
-    fn measure<F: FnOnce()>(f: F) -> Duration {
-        let start = Instant::now();
-        f();
-        start.elapsed()
-    }
-
-    /// record the duration of the sim step operation.
-    fn instrument_step<F: FnOnce()>(&self, frames: u64, f: F) {
-        let elapsed = Self::measure(f);
-        let mut me = self.0.lock().unwrap();
-        me.time_spent_stepping += elapsed;
-        me.frames_completed += frames as u64;
-    }
-
-    /// record the duration spent preparing for render (i.e. cloning stuff and moving it into a
-    /// render pool).
-    fn instrument_render_prep<F: FnOnce()>(&self, f: F) {
-        let elapsed = Self::measure(f);
-        self.0.lock().unwrap().time_spent_prepping_render += elapsed;
-    }
-
-    /// record the duration actually spent doing CPU render work
-    fn instrument_render_cpu_side<F: FnOnce()>(&self, f: F) {
-        let elapsed = Self::measure(f);
-        self.0.lock().unwrap().time_spent_rendering += elapsed;
-    }
-
-    /// record the duration spent blocking the simulation because the render queue is full.
-    fn instrument_render_blocked<F: FnOnce()>(&self, f: F) {
-        let elapsed = Self::measure(f);
-        self.0.lock().unwrap().time_spent_blocked_on_render += elapsed;
-    }
-}
-
 impl<S: AbstractSim> Driver<S> {
     pub fn new(state: S) -> Self {
         Self {
@@ -266,7 +178,6 @@ impl<S: AbstractSim + Clone + Default + Send + 'static> Driver<S> {
         });
         trace!("step end");
         if self.last_diag_time.elapsed().as_secs_f64() >= 5.0 {
-            // TODO: make this a method on the Diagnostics.
             self.last_diag_time = Instant::now();
             let step = self.state.step_no();
             let diagstr = self.diag.format();
diff --git a/crates/coremem/src/lib.rs b/crates/coremem/src/lib.rs
index 27833ab..7a25090 100644
--- a/crates/coremem/src/lib.rs
+++ b/crates/coremem/src/lib.rs
@@ -7,6 +7,7 @@
 
 use log::info;
 
+mod diagnostics;
 pub mod driver;
 pub mod geom;
 pub mod meas;