diff --git a/dsp/benches/micro.rs b/dsp/benches/micro.rs
index 0902a4c..22a2540 100644
--- a/dsp/benches/micro.rs
+++ b/dsp/benches/micro.rs
@@ -67,7 +67,7 @@ fn iir_bench() {
     let mut xy = iir::Vec5::default();
     println!(
         "int::IIR::update(s, x): {}",
-        bench_env(0.32241, |x| dut.update(&mut xy, *x))
+        bench_env(0.32241, |x| dut.update(&mut xy, *x, true))
     );
 }
 
diff --git a/dsp/src/iir.rs b/dsp/src/iir.rs
index ee9639e..a6af191 100644
--- a/dsp/src/iir.rs
+++ b/dsp/src/iir.rs
@@ -117,7 +117,7 @@ impl IIR {
     /// # Arguments
     /// * `xy` - Current filter state.
     /// * `x0` - New input.
-    pub fn update(&self, xy: &mut Vec5, x0: f32) -> f32 {
+    pub fn update(&self, xy: &mut Vec5, x0: f32, hold: bool) -> f32 {
         let n = self.ba.len();
         debug_assert!(xy.len() == n);
         // `xy` contains       x0 x1 y0 y1 y2
@@ -128,7 +128,11 @@ impl IIR {
         // Store x0            x0 x1 x2 y1 y2
         xy[0] = x0;
         // Compute y0 by multiply-accumulate
-        let y0 = macc(self.y_offset, xy, &self.ba);
+        let y0 = if hold {
+            xy[n / 2 + 1]
+        } else {
+            macc(self.y_offset, xy, &self.ba)
+        };
         // Limit y0
         let y0 = max(self.y_min, min(self.y_max, y0));
         // Store y0            x0 x1 y0 y1 y2
diff --git a/src/bin/dual-iir.rs b/src/bin/dual-iir.rs
index 0e2215b..8f07cf1 100644
--- a/src/bin/dual-iir.rs
+++ b/src/bin/dual-iir.rs
@@ -2,8 +2,6 @@
 #![no_std]
 #![no_main]
 
-use stm32h7xx_hal as hal;
-
 use stabilizer::{hardware, net};
 
 use miniconf::Miniconf;
@@ -11,20 +9,23 @@ use serde::Deserialize;
 
 use dsp::iir;
 use hardware::{
-    Adc0Input, Adc1Input, AfeGain, Dac0Output, Dac1Output, AFE0, AFE1,
+    Adc0Input, Adc1Input, AfeGain, Dac0Output, Dac1Output, DigitalInput1,
+    InputPin, AFE0, AFE1,
 };
 
-use net::{Action, MqttSettings};
+use net::{Action, MiniconfInterface};
 
 const SCALE: f32 = i16::MAX as _;
 
 // The number of cascaded IIR biquads per channel. Select 1 or 2!
 const IIR_CASCADE_LENGTH: usize = 1;
 
-#[derive(Debug, Deserialize, Miniconf)]
+#[derive(Clone, Copy, Debug, Deserialize, Miniconf)]
 pub struct Settings {
     afe: [AfeGain; 2],
     iir_ch: [[iir::IIR; IIR_CASCADE_LENGTH]; 2],
+    allow_hold: bool,
+    force_hold: bool,
 }
 
 impl Default for Settings {
@@ -32,6 +33,8 @@ impl Default for Settings {
         Self {
             afe: [AfeGain::G1, AfeGain::G1],
             iir_ch: [[iir::IIR::new(1., -SCALE, SCALE); IIR_CASCADE_LENGTH]; 2],
+            allow_hold: false,
+            force_hold: false,
         }
     }
 }
@@ -40,23 +43,23 @@ impl Default for Settings {
 const APP: () = {
     struct Resources {
         afes: (AFE0, AFE1),
+        digital_input1: DigitalInput1,
         adcs: (Adc0Input, Adc1Input),
         dacs: (Dac0Output, Dac1Output),
-        mqtt_settings: MqttSettings<Settings>,
+        mqtt_config: MiniconfInterface<Settings>,
 
         // Format: iir_state[ch][cascade-no][coeff]
         #[init([[[0.; 5]; IIR_CASCADE_LENGTH]; 2])]
         iir_state: [[iir::Vec5; IIR_CASCADE_LENGTH]; 2],
-        #[init([[iir::IIR::new(1., -SCALE, SCALE); IIR_CASCADE_LENGTH]; 2])]
-        iir_ch: [[iir::IIR; IIR_CASCADE_LENGTH]; 2],
+        settings: Settings,
     }
 
-    #[init]
+    #[init(spawn=[settings_update])]
     fn init(c: init::Context) -> init::LateResources {
         // Configure the microcontroller
         let (mut stabilizer, _pounder) = hardware::setup(c.core, c.device);
 
-        let mqtt_settings = MqttSettings::new(
+        let mqtt_config = MiniconfInterface::new(
             stabilizer.net.stack,
             "",
             "dt/sinara/stabilizer",
@@ -64,6 +67,9 @@ const APP: () = {
             stabilizer.cycle_counter,
         );
 
+        // Spawn a settings update for default settings.
+        c.spawn.settings_update().unwrap();
+
         // Enable ADC/DAC events
         stabilizer.adcs.0.start();
         stabilizer.adcs.1.start();
@@ -77,7 +83,9 @@ const APP: () = {
             afes: stabilizer.afes,
             adcs: stabilizer.adcs,
             dacs: stabilizer.dacs,
-            mqtt_settings,
+            mqtt_config,
+            digital_input1: stabilizer.digital_inputs.1,
+            settings: Settings::default(),
         }
     }
 
@@ -97,7 +105,7 @@ const APP: () = {
     ///
     /// Because the ADC and DAC operate at the same rate, these two constraints actually implement
     /// the same time bounds, meeting one also means the other is also met.
-    #[task(binds=DMA1_STR4, resources=[adcs, dacs, iir_state, iir_ch], priority=2)]
+    #[task(binds=DMA1_STR4, resources=[adcs, digital_input1, dacs, iir_state, settings], priority=2)]
     fn process(c: process::Context) {
         let adc_samples = [
             c.resources.adcs.0.acquire_buffer(),
@@ -109,13 +117,19 @@ const APP: () = {
             c.resources.dacs.1.acquire_buffer(),
         ];
 
+        let hold = c.resources.settings.force_hold
+            || (c.resources.digital_input1.is_high().unwrap()
+                && c.resources.settings.allow_hold);
+
         for channel in 0..adc_samples.len() {
             for sample in 0..adc_samples[0].len() {
-                let x = f32::from(adc_samples[channel][sample] as i16);
-                let mut y = x;
+                let mut y = f32::from(adc_samples[channel][sample] as i16);
                 for i in 0..c.resources.iir_state[channel].len() {
-                    y = c.resources.iir_ch[channel][i]
-                        .update(&mut c.resources.iir_state[channel][i], y);
+                    y = c.resources.settings.iir_ch[channel][i].update(
+                        &mut c.resources.iir_state[channel][i],
+                        y,
+                        hold,
+                    );
                 }
                 // Note(unsafe): The filter limits ensure that the value is in range.
                 // The truncation introduces 1/2 LSB distortion.
@@ -126,10 +140,14 @@ const APP: () = {
         }
     }
 
-    #[idle(resources=[mqtt_settings], spawn=[settings_update])]
+    #[idle(resources=[mqtt_config], spawn=[settings_update])]
     fn idle(mut c: idle::Context) -> ! {
         loop {
-            match c.resources.mqtt_settings.lock(|settings| settings.update()) {
+            match c
+                .resources
+                .mqtt_config
+                .lock(|config_interface| config_interface.update())
+            {
                 Some(Action::Sleep) => cortex_m::asm::wfi(),
                 Some(Action::UpdateSettings) => {
                     c.spawn.settings_update().unwrap()
@@ -139,12 +157,12 @@ const APP: () = {
         }
     }
 
-    #[task(priority = 1, resources=[mqtt_settings, afes, iir_ch])]
+    #[task(priority = 1, resources=[mqtt_config, afes, settings])]
     fn settings_update(mut c: settings_update::Context) {
-        let settings = &c.resources.mqtt_settings.mqtt.settings;
+        let settings = &c.resources.mqtt_config.mqtt.settings;
 
         // Update the IIR channels.
-        c.resources.iir_ch.lock(|iir| *iir = settings.iir_ch);
+        c.resources.settings.lock(|current| *current = *settings);
 
         // Update AFEs
         c.resources.afes.0.set_gain(settings.afe[0]);
@@ -153,7 +171,7 @@ const APP: () = {
 
     #[task(binds = ETH, priority = 1)]
     fn eth(_: eth::Context) {
-        unsafe { hal::ethernet::interrupt_handler() }
+        unsafe { stm32h7xx_hal::ethernet::interrupt_handler() }
     }
 
     #[task(binds = SPI2, priority = 3)]
diff --git a/src/bin/lockin-external.rs b/src/bin/lockin-external.rs
index b62ea42..36bd882 100644
--- a/src/bin/lockin-external.rs
+++ b/src/bin/lockin-external.rs
@@ -14,7 +14,7 @@ use stabilizer::hardware::{
 };
 
 use miniconf::Miniconf;
-use stabilizer::net::{Action, MqttSettings};
+use stabilizer::net::{Action, MiniconfInterface};
 
 #[derive(Copy, Clone, Debug, Deserialize, Miniconf)]
 enum Conf {
@@ -58,7 +58,7 @@ const APP: () = {
         afes: (AFE0, AFE1),
         adcs: (Adc0Input, Adc1Input),
         dacs: (Dac0Output, Dac1Output),
-        mqtt_settings: MqttSettings<Settings>,
+        mqtt_config: MiniconfInterface<Settings>,
         settings: Settings,
 
         timestamper: InputStamper,
@@ -71,7 +71,7 @@ const APP: () = {
         // Configure the microcontroller
         let (mut stabilizer, _pounder) = setup(c.core, c.device);
 
-        let mqtt_settings = MqttSettings::new(
+        let mqtt_config = MiniconfInterface::new(
             stabilizer.net.stack,
             "",
             "dt/sinara/lockin",
@@ -108,7 +108,7 @@ const APP: () = {
             afes: stabilizer.afes,
             adcs: stabilizer.adcs,
             dacs: stabilizer.dacs,
-            mqtt_settings,
+            mqtt_config,
             timestamper: stabilizer.timestamper,
 
             settings,
@@ -190,10 +190,14 @@ const APP: () = {
         }
     }
 
-    #[idle(resources=[mqtt_settings], spawn=[settings_update])]
+    #[idle(resources=[mqtt_config], spawn=[settings_update])]
     fn idle(mut c: idle::Context) -> ! {
         loop {
-            match c.resources.mqtt_settings.lock(|settings| settings.update()) {
+            match c
+                .resources
+                .mqtt_config
+                .lock(|config_interface| config_interface.update())
+            {
                 Some(Action::Sleep) => cortex_m::asm::wfi(),
                 Some(Action::UpdateSettings) => {
                     c.spawn.settings_update().unwrap()
@@ -203,9 +207,9 @@ const APP: () = {
         }
     }
 
-    #[task(priority = 1, resources=[mqtt_settings, settings, afes])]
+    #[task(priority = 1, resources=[mqtt_config, settings, afes])]
     fn settings_update(mut c: settings_update::Context) {
-        let settings = &c.resources.mqtt_settings.mqtt.settings;
+        let settings = &c.resources.mqtt_config.mqtt.settings;
 
         c.resources.afes.0.set_gain(settings.afe[0]);
         c.resources.afes.1.set_gain(settings.afe[1]);
diff --git a/src/hardware/configuration.rs b/src/hardware/configuration.rs
index 4d116ff..5bc5a20 100644
--- a/src/hardware/configuration.rs
+++ b/src/hardware/configuration.rs
@@ -13,8 +13,8 @@ use embedded_hal::digital::v2::{InputPin, OutputPin};
 
 use super::{
     adc, afe, cycle_counter::CycleCounter, dac, design_parameters,
-    digital_input_stamper, eeprom, pounder, timers, DdsOutput, EthernetPhy,
-    NetworkStack, AFE0, AFE1,
+    digital_input_stamper, eeprom, pounder, timers, DdsOutput, DigitalInput0,
+    DigitalInput1, EthernetPhy, NetworkStack, AFE0, AFE1,
 };
 
 pub struct NetStorage {
@@ -69,6 +69,7 @@ pub struct StabilizerDevices {
     pub timestamp_timer: timers::TimestampTimer,
     pub net: NetworkDevices,
     pub cycle_counter: CycleCounter,
+    pub digital_inputs: (DigitalInput0, DigitalInput1),
 }
 
 /// The available Pounder-specific hardware interfaces.
@@ -439,6 +440,12 @@ pub fn setup(
         )
     };
 
+    let digital_inputs = {
+        let di0 = gpiog.pg9.into_floating_input();
+        let di1 = gpioc.pc15.into_floating_input();
+        (di0, di1)
+    };
+
     let mut eeprom_i2c = {
         let sda = gpiof.pf0.into_alternate_af4().set_open_drain();
         let scl = gpiof.pf1.into_alternate_af4().set_open_drain();
@@ -884,6 +891,7 @@ pub fn setup(
         adc_dac_timer: sampling_timer,
         timestamp_timer,
         cycle_counter,
+        digital_inputs,
     };
 
     // info!("Version {} {}", build_info::PKG_VERSION, build_info::GIT_VERSION.unwrap());
diff --git a/src/hardware/mod.rs b/src/hardware/mod.rs
index 60e7768..d3e5711 100644
--- a/src/hardware/mod.rs
+++ b/src/hardware/mod.rs
@@ -1,6 +1,9 @@
 ///! Module for all hardware-specific setup of Stabilizer
 use stm32h7xx_hal as hal;
 
+// Re-export for the DigitalInputs below:
+pub use embedded_hal::digital::v2::InputPin;
+
 #[cfg(feature = "semihosting")]
 use panic_semihosting as _;
 
@@ -34,6 +37,14 @@ pub type AFE1 = afe::ProgrammableGainAmplifier<
     hal::gpio::gpiod::PD15<hal::gpio::Output<hal::gpio::PushPull>>,
 >;
 
+// Type alias for digital input 0 (DI0).
+pub type DigitalInput0 =
+    hal::gpio::gpiog::PG9<hal::gpio::Input<hal::gpio::Floating>>;
+
+// Type alias for digital input 1 (DI1).
+pub type DigitalInput1 =
+    hal::gpio::gpioc::PC15<hal::gpio::Input<hal::gpio::Floating>>;
+
 pub type NetworkStack = smoltcp_nal::NetworkStack<
     'static,
     'static,
diff --git a/src/net/mod.rs b/src/net/mod.rs
index f38f3d9..23d712d 100644
--- a/src/net/mod.rs
+++ b/src/net/mod.rs
@@ -2,7 +2,7 @@ use crate::hardware::{
     design_parameters::MQTT_BROKER, CycleCounter, EthernetPhy, NetworkStack,
 };
 
-use miniconf::{minimq, MqttInterface};
+use miniconf::minimq;
 
 /// Potential actions for firmware to take.
 pub enum Action {
@@ -14,17 +14,17 @@ pub enum Action {
 }
 
 /// MQTT settings interface.
-pub struct MqttSettings<S>
+pub struct MiniconfInterface<S>
 where
     S: miniconf::Miniconf + Default,
 {
-    pub mqtt: MqttInterface<S, NetworkStack, minimq::consts::U256>,
+    pub mqtt: miniconf::MqttInterface<S, NetworkStack, minimq::consts::U256>,
     clock: CycleCounter,
     phy: EthernetPhy,
     network_was_reset: bool,
 }
 
-impl<S> MqttSettings<S>
+impl<S> MiniconfInterface<S>
 where
     S: miniconf::Miniconf + Default,
 {
@@ -49,7 +49,8 @@ where
                     .unwrap()
             };
 
-            MqttInterface::new(mqtt_client, prefix, S::default()).unwrap()
+            miniconf::MqttInterface::new(mqtt_client, prefix, S::default())
+                .unwrap()
         };
 
         Self {