diff --git a/deploy.sh b/deploy.sh
index e146bdc..67d7bcb 100755
--- a/deploy.sh
+++ b/deploy.sh
@@ -53,6 +53,12 @@ if [[ -f "$SRC_DIR/rust/pm-kit/pm-kit.uf2" ]]; then
   cp "$SRC_DIR/rust/pm-kit/pm-kit.uf2" "$DEST_DIR/pm-kit.uf2"
   echo "  pm-kit.uf2 ($(stat -c '%s' "$DEST_DIR/pm-kit.uf2") bytes)  # Rust RP2350 firmware (alpha live metronome)"
 fi
+# ELF with defmt info — `probe-rs run --chip RP235x pm-kit.elf` flashes over the Debug Probe and
+# streams logs/panics. Needed locally (not the uf2) because defmt decodes log strings from the ELF.
+if [[ -f "$SRC_DIR/rust/pm-kit/pm-kit.elf" ]]; then
+  cp "$SRC_DIR/rust/pm-kit/pm-kit.elf" "$DEST_DIR/pm-kit.elf"
+  echo "  pm-kit.elf ($(stat -c '%s' "$DEST_DIR/pm-kit.elf") bytes)  # probe-rs flash + defmt RTT logging"
+fi
 cp "$DIST_DIR/pm_k1_circuitpy.zip" "$DEST_DIR/pm_k1_circuitpy.zip"; echo "  pm_k1_circuitpy.zip ($(stat -c '%s' "$DEST_DIR/pm_k1_circuitpy.zip") bytes)"  # PM_K-1 CircuitPython bundle
 cp "$DIST_DIR/pico-cp-app.py" "$DEST_DIR/pico-cp-app.py"; echo "  pico-cp-app.py ($(stat -c '%s' "$DEST_DIR/pico-cp-app.py") bytes)"  # served for version reading + reference
 cp "$DIST_DIR/pico-cp-app.mpy" "$DEST_DIR/pico-cp-app.mpy"; echo "  pico-cp-app.mpy ($(stat -c '%s' "$DEST_DIR/pico-cp-app.mpy") bytes)"  # precompiled firmware the editor pushes (base64)
diff --git a/rust/Containerfile b/rust/Containerfile
index af5dabe..3c8c5d0 100644
--- a/rust/Containerfile
+++ b/rust/Containerfile
@@ -3,6 +3,8 @@
 FROM docker.io/library/rust:1-slim
 
 # Cortex-M33 target for the eventual RP2350 firmware. Harmless for the host tests.
-RUN rustup target add thumbv8m.main-none-eabihf
+RUN rustup target add thumbv8m.main-none-eabihf \
+ && rustup component add llvm-tools-preview \
+ && cargo install flip-link    # stack-overflow-safe linker (overflow faults instead of corrupting statics)
 
 WORKDIR /work/rust
diff --git a/rust/pm-kit/.cargo/config.toml b/rust/pm-kit/.cargo/config.toml
index 910819a..efbae5a 100644
--- a/rust/pm-kit/.cargo/config.toml
+++ b/rust/pm-kit/.cargo/config.toml
@@ -2,7 +2,16 @@
 target = "thumbv8m.main-none-eabihf"
 
 [target.thumbv8m.main-none-eabihf]
+# flip-link: places the stack BELOW the statics so a stack overflow hits a guard region
+# and faults cleanly instead of silently corrupting .bss/.data (e.g. the SPI buffer → black screen).
+linker = "flip-link"
+# `cargo run` flashes over the Raspberry Pi Debug Probe and streams defmt logs/panics via RTT.
+runner = "probe-rs run --chip RP235x"
 rustflags = [
   "-C", "link-arg=--nmagic",
   "-C", "link-arg=-Tlink.x",
+  "-C", "link-arg=-Tdefmt.x",   # defmt's linker section for log-string interning
 ]
+
+[env]
+DEFMT_LOG = "debug"
diff --git a/rust/pm-kit/.gitignore b/rust/pm-kit/.gitignore
index 76f1255..6599781 100644
--- a/rust/pm-kit/.gitignore
+++ b/rust/pm-kit/.gitignore
@@ -2,3 +2,4 @@ target/
 Cargo.lock
 *.uf2
 *.bin
+*.elf
diff --git a/rust/pm-kit/Cargo.toml b/rust/pm-kit/Cargo.toml
index 7db251e..1f4352b 100644
--- a/rust/pm-kit/Cargo.toml
+++ b/rust/pm-kit/Cargo.toml
@@ -5,9 +5,11 @@ edition = "2021"
 description = "PM_K-1 firmware (RP2350 / Pico 2). Stage 3 bring-up: boot blink → display → drivers + pm-core."
 
 [dependencies]
-rp235x-hal = { version = "0.3", features = ["binary-info", "critical-section-impl", "rt"] }
+rp235x-hal = { version = "0.3", features = ["binary-info", "critical-section-impl", "rt", "defmt"] }
 cortex-m-rt = "0.7"
-panic-halt = "1"
+defmt = "0.3"
+defmt-rtt = "0.4"
+panic-probe = { version = "0.3", features = ["print-defmt"] }
 embedded-hal = "1"
 embedded-hal-0-2 = { package = "embedded-hal", version = "0.2.7" } # ADC OneShot trait (rp235x-hal ADC)
 embedded-hal-bus = "0.2"
diff --git a/rust/pm-kit/build.sh b/rust/pm-kit/build.sh
index 2cb19d1..ed4482f 100755
--- a/rust/pm-kit/build.sh
+++ b/rust/pm-kit/build.sh
@@ -10,7 +10,7 @@ set -euo pipefail
 DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"   # rust/pm-kit
 REPO="$(cd "$DIR/../.." && pwd)"                       # repo root
 RUNTIME="${RUNTIME:-podman}"
-IMG="pm-rust:1"
+IMG="pm-rust:2"
 
 "$RUNTIME" run --rm -v "$REPO":/work:Z -w /work/rust/pm-kit "$IMG" bash -c '
   set -e
diff --git a/rust/pm-kit/src/main.rs b/rust/pm-kit/src/main.rs
index 8cbaec0..7f0c241 100644
--- a/rust/pm-kit/src/main.rs
+++ b/rust/pm-kit/src/main.rs
@@ -23,7 +23,9 @@ use mipidsi::interface::{Interface, SpiInterface};
 use mipidsi::models::ST7796;
 use mipidsi::options::{ColorInversion, ColorOrder, Orientation};
 use mipidsi::Builder;
-use panic_halt as _;
+use defmt::info;
+use defmt_rtt as _; // global defmt logger over RTT (read by `probe-rs run`)
+use panic_probe as _; // panic handler that prints the message + location over defmt, then halts
 use rp235x_hal as hal;
 use hal::fugit::RateExtU32;
 use hal::Clock;
@@ -57,12 +59,13 @@ impl OutputPin for NoCs {
 #[hal::entry]
 fn main() -> ! {
     // heap for track parsing (track-format uses alloc). RP2350 has 520 KB SRAM.
+    const HEAP_SIZE: usize = 96 * 1024;
     {
         use core::mem::MaybeUninit;
-        const HEAP_SIZE: usize = 16 * 1024;
         static mut HEAP_MEM: [MaybeUninit<u8>; HEAP_SIZE] = [MaybeUninit::uninit(); HEAP_SIZE];
         unsafe { HEAP.init(core::ptr::addr_of_mut!(HEAP_MEM) as usize, HEAP_SIZE) }
     }
+    info!("== pm-kit boot == heap {}KB, {} free", HEAP_SIZE / 1024, HEAP.free());
 
     let mut pac = hal::pac::Peripherals::take().unwrap();
     let mut watchdog = hal::Watchdog::new(pac.WATCHDOG);
@@ -149,24 +152,161 @@ fn main() -> ! {
         .orientation(Orientation::new().flip_horizontal())
         .init(&mut timer)
         .unwrap();
+    info!("display init ok, {} free", HEAP.free());
 
-    // ---- MINIMAL ISOLATION ----
-    // Heap is initialised above. Exercise the allocator once (parse), then just draw the
-    // confirmed-working pattern in a loop. No inputs/audio/clock. If the screen shows blue +
-    // corners → heap + parse + display are all fine and the bug is in the metronome loop logic.
-    // If still black → the heap/parse path breaks the display.
-    // (parse removed for this test — heap init only)
+    // ---- inputs + speaker ----
+    let mut btn_a = pins.gpio15.into_pull_up_input(); // A = play/stop
+    let mut btn_b = pins.gpio14.into_pull_up_input(); // B = grid/notation view
+    let mut adc = hal::adc::Adc::new(pac.ADC, &mut pac.RESETS);
+    let mut joy_x = hal::adc::AdcPin::new(pins.gpio26).unwrap();
+    let mut joy_y = hal::adc::AdcPin::new(pins.gpio27).unwrap();
+    let pwm_slices = hal::pwm::Slices::new(pac.PWM, &mut pac.RESETS);
+    let mut spk = pwm_slices.pwm6; // GP13 = PWM slice 6, channel B
+    spk.set_div_int(125);
+    spk.set_top(600); // ~2 kHz click
+    spk.enable();
+    spk.channel_b.output_to(pins.gpio13);
+
+    // ---- built-in grooves ----
+    const GROOVES: [&str; 4] = [
+        "t120;kick:4=X.x.;snare:4=.X.X;hatClosed:4/2=xxxxxxxx",
+        "t92;kick:4/3=X....x...x..;snare:4/3=..gg.gX.gg.g;hatClosed:4/3=X.xX.xX.xX.x",
+        "t140;kick:4=X..x;snare:4=.X.X;hatClosed:4/4=xxxxxxxxxxxxxxxx",
+        "t100;kick:4=Xxxx;claves:5=Xxxxx~",
+    ];
+    const NAMES: [&str; 4] = ["Four on the floor", "Half-time shuffle", "Driving 16ths", "5 over 4"];
+
+    let mut idx = 0usize;
+    let mut track = track_format::parse(GROOVES[idx]);
+    info!("parsed groove 0: bpm={} lanes={}, {} free", track.bpm, track.lanes.len(), HEAP.free());
+    let mut tempo: i64 = track.bpm;
+    let mut playing = true;
+    let mut notation = false;
+
+    let mut bar_start = timer.get_counter().ticks();
+    let mut last_step = usize::MAX;
+    let mut click_off_us: u64 = 0;
+    let (mut pa, mut pb) = (false, false);
+    let mut joy_zone = 0i8;
+    let mut full_redraw = true;
+    let mut last_draw_us = 0u64;
     let mut hb = false;
     let mut hb_us = 0u64;
+    let mut last_draw_ok = false;
     led.set_low().unwrap();
+    info!("entering main loop");
+
     loop {
-        pm_ui::draw_ui(&mut display).ok();
         let now = timer.get_counter().ticks();
+
+        // ---- inputs ----
+        let a = btn_a.is_low().unwrap_or(false);
+        let b = btn_b.is_low().unwrap_or(false);
+        if a && !pa {
+            playing = !playing;
+            if playing {
+                bar_start = now;
+                last_step = usize::MAX;
+            }
+            full_redraw = true;
+        }
+        if b && !pb {
+            notation = !notation;
+            full_redraw = true;
+        }
+        pa = a;
+        pb = b;
+
+        let jx = adc.read(&mut joy_x).unwrap_or(2048);
+        let jy = adc.read(&mut joy_y).unwrap_or(2048);
+        // rotate the joystick reading 90° CCW for control
+        let rx = jy as i32;
+        let ry = 4095 - jx as i32;
+        let zone: i8 = if ry > 3200 { 1 } else if ry < 900 { 2 } else if rx > 3200 { 3 } else if rx < 900 { 4 } else { 0 };
+        if zone != 0 && joy_zone == 0 {
+            match zone {
+                1 => tempo = (tempo + 4).min(300),                 // up → tempo+
+                2 => tempo = (tempo - 4).max(30),                  // down → tempo-
+                3 => {
+                    idx = (idx + 1) % GROOVES.len();               // right → next groove
+                    track = track_format::parse(GROOVES[idx]);
+                    tempo = track.bpm;
+                    bar_start = now;
+                    last_step = usize::MAX;
+                }
+                4 => {
+                    idx = (idx + GROOVES.len() - 1) % GROOVES.len(); // left → prev
+                    track = track_format::parse(GROOVES[idx]);
+                    tempo = track.bpm;
+                    bar_start = now;
+                    last_step = usize::MAX;
+                }
+                _ => {}
+            }
+            full_redraw = true;
+        }
+        joy_zone = zone;
+
+        // ---- clock ----
+        let master = &track.lanes[0];
+        let msteps = master.levels.len().max(1) as u64;
+        let beats = master.groups.iter().map(|&g| g as u64).sum::<u64>().max(1);
+        let bar_us = 60_000_000u64 * beats / tempo.max(1) as u64;
+        let step_us = (bar_us / msteps).max(1);
+        let elapsed = now.wrapping_sub(bar_start) % bar_us;
+        let cur_step = (elapsed / step_us) as usize;
+        let phase = elapsed as f32 / bar_us as f32;
+
+        // ---- audio: click on a new step that has a hit ----
+        if playing && cur_step != last_step {
+            let lvl = master.levels[cur_step.min(msteps as usize - 1)];
+            if lvl > 0 {
+                let _ = spk.channel_b.set_duty_cycle(if lvl == 2 { 380 } else { 240 });
+                click_off_us = now + if lvl == 2 { 28_000 } else { 14_000 };
+            }
+            last_step = cur_step;
+        }
+        if now >= click_off_us {
+            let _ = spk.channel_b.set_duty_cycle(0);
+        }
+
+        // ---- draw: on change, and periodically (so a draw lost right after init reappears, and
+        // the playhead advances). ~7 fps; partial/playhead-only redraw is the next optimization. ----
+        if full_redraw || now.wrapping_sub(last_draw_us) > 140_000 {
+            let lanes: Vec<pm_ui::LaneView> = track
+                .lanes
+                .iter()
+                .map(|l| pm_ui::LaneView {
+                    name: &l.sound,
+                    levels: &l.levels,
+                    beats: l.groups.iter().map(|&g| g as u32).sum::<u32>().min(255) as u8,
+                    poly: l.poly,
+                    muted: l.mute,
+                })
+                .collect();
+            let screen = pm_ui::Screen { name: NAMES[idx], bpm: tempo, playing, phase, lanes: &lanes };
+            last_draw_ok = if notation {
+                pm_ui::draw_notation(&mut display, &screen).is_ok()
+            } else {
+                pm_ui::draw_metronome(&mut display, &screen).is_ok()
+            };
+            full_redraw = false;
+            last_draw_us = now;
+        }
+
+        // heartbeat LED + log (~2 Hz) — confirms the loop is alive and the last draw returned Ok
         if now.wrapping_sub(hb_us) > 500_000 {
             hb = !hb;
             let _ = if hb { led.set_high() } else { led.set_low() };
+            info!("alive: idx={} step={} playing={} draw_ok={} free={}", idx, cur_step, playing, last_draw_ok, HEAP.free());
             hb_us = now;
         }
-        timer.delay_ms(50);
+        timer.delay_ms(8);
     }
 }
+
+/// picotool metadata (visible via `picotool info`).
+#[link_section = ".bi_entries"]
+#[used]
+pub static PICOTOOL_ENTRIES: [hal::binary_info::EntryAddr; 1] =
+    [hal::binary_info::rp_program_name!(c"pm-kit display")];
diff --git a/rust/run.sh b/rust/run.sh
index 43a4ea5..f5e1fd4 100755
--- a/rust/run.sh
+++ b/rust/run.sh
@@ -8,7 +8,7 @@
 # Override the runtime with RUNTIME=docker ./run.sh ...
 set -euo pipefail
 
-IMG="pm-rust:1"
+IMG="pm-rust:2"
 RUST_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"   # rust/
 REPO_DIR="$(cd "$RUST_DIR/.." && pwd)"                     # repo root
 RUNTIME="${RUNTIME:-podman}"