diff --git a/rust/pm-kit/src/main.rs b/rust/pm-kit/src/main.rs
index ee9cae0..3bdd3c7 100644
--- a/rust/pm-kit/src/main.rs
+++ b/rust/pm-kit/src/main.rs
@@ -150,144 +150,23 @@ fn main() -> ! {
         .init(&mut timer)
         .unwrap();
 
-    // ---- 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]);
-    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;
+    // ---- 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.
+    let _t = track_format::parse("t120;kick:4=Xxxx;snare:4=.X.X");
     let mut hb = false;
     let mut hb_us = 0u64;
     led.set_low().unwrap();
-
     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 {
-            // DIAGNOSTIC: draw the confirmed-working bring-up pattern instead of the metronome,
-            // to isolate whether the blank screen is draw_metronome or the heap/display path.
-            // If you see blue + 4 colored corners + "TL"/"PMK" → display+heap are fine and the
-            // bug is in draw_metronome. If still black → it's the heap/display, not the drawing.
-            let _ = (notation, idx, tempo, phase, &track); // keep state alive while diagnosing
-            pm_ui::draw_ui(&mut display).ok();
-            full_redraw = false;
-            last_draw_us = now;
-        }
-
-        // heartbeat LED (~1 Hz)
         if now.wrapping_sub(hb_us) > 500_000 {
             hb = !hb;
             let _ = if hb { led.set_high() } else { led.set_low() };
             hb_us = now;
         }
-        timer.delay_ms(8);
+        timer.delay_ms(50);
     }
 }
-
-/// 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")];