diff --git a/src/bin/lockin-internal-demo.rs b/src/bin/lockin-internal-demo.rs
new file mode 100644
index 0000000..54a429f
--- /dev/null
+++ b/src/bin/lockin-internal-demo.rs
@@ -0,0 +1,160 @@
+#![deny(warnings)]
+#![no_std]
+#![no_main]
+#![cfg_attr(feature = "nightly", feature(core_intrinsics))]
+
+// A constant sinusoid to send on the DAC output.
+const DAC_SEQUENCE: [f32; 8] =
+    [0.0, 0.707, 1.0, 0.707, 0.0, -0.707, -1.0, -0.707];
+
+use dsp::{iir_int, lockin::Lockin};
+use hardware::{Adc1Input, Dac0Output, Dac1Output, AFE0, AFE1};
+use stabilizer::hardware;
+
+#[rtic::app(device = stm32h7xx_hal::stm32, peripherals = true, monotonic = rtic::cyccnt::CYCCNT)]
+const APP: () = {
+    struct Resources {
+        afes: (AFE0, AFE1),
+        adc1: Adc1Input,
+        dacs: (Dac0Output, Dac1Output),
+
+        lockin: Lockin,
+    }
+
+    #[init]
+    fn init(c: init::Context) -> init::LateResources {
+        // Configure the microcontroller
+        let (mut stabilizer, _pounder) = hardware::setup(c.core, c.device);
+
+        let lockin = Lockin::new(
+            &iir_int::IIRState::lowpass(1e-3, 0.707, 2.), // TODO: expose
+        );
+
+        // Enable ADC/DAC events
+        stabilizer.adcs.1.start();
+        stabilizer.dacs.0.start();
+        stabilizer.dacs.1.start();
+
+        // Start sampling ADCs.
+        stabilizer.adc_dac_timer.start();
+
+        init::LateResources {
+            lockin,
+            afes: stabilizer.afes,
+            adc1: stabilizer.adcs.1,
+            dacs: stabilizer.dacs,
+        }
+    }
+
+    /// Main DSP processing routine for Stabilizer.
+    ///
+    /// # Note
+    /// Processing time for the DSP application code is bounded by the following constraints:
+    ///
+    /// DSP application code starts after the ADC has generated a batch of samples and must be
+    /// completed by the time the next batch of ADC samples has been acquired (plus the FIFO buffer
+    /// time). If this constraint is not met, firmware will panic due to an ADC input overrun.
+    ///
+    /// The DSP application code must also fill out the next DAC output buffer in time such that the
+    /// DAC can switch to it when it has completed the current buffer. If this constraint is not met
+    /// it's possible that old DAC codes will be generated on the output and the output samples will
+    /// be delayed by 1 batch.
+    ///
+    /// 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.
+    ///
+    /// TODO: Document
+    #[task(binds=DMA1_STR4, resources=[adc1, dacs, lockin], priority=2)]
+    fn process(c: process::Context) {
+        let adc_samples = c.resources.adc1.acquire_buffer();
+        let dac_samples = [
+            c.resources.dacs.0.acquire_buffer(),
+            c.resources.dacs.1.acquire_buffer(),
+        ];
+
+        // DAC0 always generates a fixed sinusoidal output.
+        for (i, value) in DAC_SEQUENCE.iter().enumerate() {
+            // Full-scale gives a +/- 12V amplitude waveform. Scale it down to give +/- 100mV.
+            let y = value * i16::MAX as f32 / 120.0;
+            // Note(unsafe): The DAC_SEQUENCE values are guaranteed to be normalized.
+            let y = unsafe { y.to_int_unchecked::<i16>() };
+
+            // Convert to DAC code
+            dac_samples[0][i] = y as u16 ^ 0x8000;
+        }
+
+        let pll_phase = 0;
+        let pll_frequency = 1i32 << (32 - 3); // 1/8 of the sample rate
+
+        // Harmonic index of the LO: -1 to _de_modulate the fundamental
+        let harmonic: i32 = -1;
+
+        // Demodulation LO phase offset
+        let phase_offset: i32 = (0.7495 * i32::MAX as f32) as i32;
+        let sample_frequency = (pll_frequency as i32).wrapping_mul(harmonic);
+        let mut sample_phase = phase_offset
+            .wrapping_add((pll_phase as i32).wrapping_mul(harmonic));
+
+        let mut phase = 0i16;
+
+        for sample in adc_samples.iter() {
+            // Convert to signed, MSB align the ADC sample.
+            let input = (*sample as i16 as i32) << 16;
+
+            // Obtain demodulated, filtered IQ sample.
+            let output = c.resources.lockin.update(input, sample_phase);
+
+            // Advance the sample phase.
+            sample_phase = sample_phase.wrapping_add(sample_frequency);
+
+            // Convert from IQ to phase. Scale the phase so that it fits in the DAC range. We do
+            // this by shifting it down into the 16-bit range.
+            phase = (output.phase() >> 16) as i16;
+        }
+
+        for value in dac_samples[1].iter_mut() {
+            *value = phase as u16 ^ 0x8000
+        }
+    }
+
+    #[idle(resources=[afes])]
+    fn idle(_: idle::Context) -> ! {
+        loop {
+            // TODO: Implement network interface.
+            cortex_m::asm::wfi();
+        }
+    }
+
+    #[task(binds = ETH, priority = 1)]
+    fn eth(_: eth::Context) {
+        unsafe { stm32h7xx_hal::ethernet::interrupt_handler() }
+    }
+
+    #[task(binds = SPI2, priority = 3)]
+    fn spi2(_: spi2::Context) {
+        panic!("ADC0 input overrun");
+    }
+
+    #[task(binds = SPI3, priority = 3)]
+    fn spi3(_: spi3::Context) {
+        panic!("ADC1 input overrun");
+    }
+
+    #[task(binds = SPI4, priority = 3)]
+    fn spi4(_: spi4::Context) {
+        panic!("DAC0 output error");
+    }
+
+    #[task(binds = SPI5, priority = 3)]
+    fn spi5(_: spi5::Context) {
+        panic!("DAC1 output error");
+    }
+
+    extern "C" {
+        // hw interrupt handlers for RTIC to use for scheduling tasks
+        // one per priority
+        fn DCMI();
+        fn JPEG();
+        fn SDMMC();
+    }
+};