perf(ui-lvgl): lower clock when idle, fewer redraws, wake on BLE frames

- CPU at 80 MHz with the screen on after 2 s without touch or animation;
  a touch restores the full clock before its frame is drawn
- setText(): periodic refreshes no longer redraw unchanged labels
  (status bar, Home, lock, Diag, GPS, compass, clock, map, nav, nearby)
- map markers kept across the 3 s rebuild when unchanged
- app connected: the loop blocks until a BLE frame arrives
  (serialFrameArrived / hasPendingFrames) instead of polling every 2 ms
- PSRAM: boot frame sprite and the HTTP response buffer released

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/companion_radio/ui-lvgl/ClockScreen.h

@@ -226,16 +226,16 @@ void UITask::refreshClock() {
     if (s_big) {
       char b[16];
       fmtRemaining(b, sizeof(b), _core->clock.timerRemainingMs());
-      lv_label_set_text(s_big, b);
+      setText(s_big, b);
     }
-    if (s_go_lbl) lv_label_set_text(s_go_lbl, running ? LV_SYMBOL_STOP " Stop" : LV_SYMBOL_PLAY " Start");
+    if (s_go_lbl) setText(s_go_lbl, running ? LV_SYMBOL_STOP " Stop" : LV_SYMBOL_PLAY " Start");
   } else if (s_tab == TAB_STOPWATCH) {
     if (s_big) {
       char b[16];
       fmtStopwatch(b, sizeof(b), swElapsed());
-      lv_label_set_text(s_big, b);
+      setText(s_big, b);
     }
-    if (s_go_lbl) lv_label_set_text(s_go_lbl, s_sw_running ? LV_SYMBOL_PAUSE " Stop" : LV_SYMBOL_PLAY " Start");
+    if (s_go_lbl) setText(s_go_lbl, s_sw_running ? LV_SYMBOL_PAUSE " Stop" : LV_SYMBOL_PLAY " Start");
   }
 }
 

examples/companion_radio/ui-lvgl/CompassScreen.h

@@ -127,14 +127,14 @@ void UITask::refreshCompass() {
     lv_obj_invalidate(s_dial);
   }
   if (have) {
-    lv_label_set_text_fmt(s_deg, "%03d", cog);
+    setTextFmt(s_deg, "%03d", cog);
-    lv_label_set_text(s_degsign, "\xC2\xB0");
+    setText(s_degsign, "\xC2\xB0");
-    lv_label_set_text(s_card, geo::bearingCardinal(cog));
+    setText(s_card, geo::bearingCardinal(cog));
-    lv_label_set_text(s_hint, "Course over ground");
+    setText(s_hint, "Course over ground");
   } else {
-    lv_label_set_text(s_deg, "");
+    setText(s_deg, "");
-    lv_label_set_text(s_degsign, "");
+    setText(s_degsign, "");
-    lv_label_set_text(s_card, "--");
+    setText(s_card, "--");
-    lv_label_set_text(s_hint, hint);
+    setText(s_hint, hint);
   }
 }

examples/companion_radio/ui-lvgl/DeviceScreen.h

@@ -288,21 +288,21 @@ void UITask::refreshLock() {
     clockFaceSet(s_lock_clock, &ti, _prefs);
     char date[48];
     fmtDate(date, sizeof(date), ti);
-    if (s_lock_date) lv_label_set_text(s_lock_date, date);
+    if (s_lock_date) setText(s_lock_date, date);
   }
   int unread = unreadTotal();
   if (!s_lock_date) {   // PIN card: the count next to the clock, the keypad's line
-    if (unread > 0) lv_label_set_text_fmt(s_lock_unread, LV_SYMBOL_ENVELOPE " %d", unread);
+    if (unread > 0) setTextFmt(s_lock_unread, LV_SYMBOL_ENVELOPE " %d", unread);
-    else lv_label_set_text(s_lock_unread, "");
+    else setText(s_lock_unread, "");
     if (!s_pin_msg) return;
     bool was = _pin_tries.block_until != 0;
-    if (_pin_tries.blocked()) lv_label_set_text_fmt(s_pin_msg, "Too many tries - wait %lu s", (unsigned long)_pin_tries.secondsLeft());
+    if (_pin_tries.blocked()) setTextFmt(s_pin_msg, "Too many tries - wait %lu s", (unsigned long)_pin_tries.secondsLeft());
-    else if (was) lv_label_set_text(s_pin_msg, "Enter PIN");
+    else if (was) setText(s_pin_msg, "Enter PIN");
-    else if (!lv_label_get_text(s_pin_msg)[0]) lv_label_set_text(s_pin_msg, "Enter PIN");
+    else if (!lv_label_get_text(s_pin_msg)[0]) setText(s_pin_msg, "Enter PIN");
     return;
   }
-  if (unread > 0) lv_label_set_text_fmt(s_lock_unread, LV_SYMBOL_ENVELOPE "  %d new message%s", unread, unread == 1 ? "" : "s");
+  if (unread > 0) setTextFmt(s_lock_unread, LV_SYMBOL_ENVELOPE "  %d new message%s", unread, unread == 1 ? "" : "s");
-  else lv_label_set_text(s_lock_unread, "");
+  else setText(s_lock_unread, "");
 }
 
 // ── Screen PIN ────────────────────────────────────────────────────────────────

examples/companion_radio/ui-lvgl/DiagScreen.h

@@ -91,13 +91,13 @@ static void setLive(int i, const diag::Row& r) {
     const char* slash = strchr(r.value, '/');
     char a[12];
     snprintf(a, sizeof(a), "%.*s", slash ? (int)(slash - r.value) : (int)strlen(r.value), r.value);
-    lv_label_set_text(lv.in, a);
+    setText(lv.in, a);
-    lv_label_set_text(lv.out, slash ? slash + 1 : "");
+    setText(lv.out, slash ? slash + 1 : "");
     return;
   }
   char v[40];
   showValue(r.label, r.value, v, sizeof(v));
-  lv_label_set_text(lv.val, v);
+  setText(lv.val, v);
   if (!strcmp(r.label, "Errors")) lv_obj_set_style_text_color(lv.val, lv_color_hex(strcmp(r.value, "OK") ? theme::FAIL : theme::OK), 0);
 }
 

examples/companion_radio/ui-lvgl/GpsScreen.h

@@ -324,13 +324,13 @@ void UITask::refreshGps() {
   char pos[32] = "", alt[16] = "", speed[16] = "", dop[32] = "";
   bool fix = false;
   if (!g) {
-    lv_label_set_text(s_status, "Not available");
+    setText(s_status, "Not available");
     lv_obj_set_style_text_color(s_status, lv_color_hex(theme::TEXT_MUTED), 0);
   } else if (off) {
-    lv_label_set_text(s_status, "GPS is off");
+    setText(s_status, "GPS is off");
     lv_obj_set_style_text_color(s_status, lv_color_hex(theme::TEXT_MUTED), 0);
   } else if (!data) {
-    lv_label_set_text(s_status, "No data");
+    setText(s_status, "No data");
     lv_obj_set_style_text_color(s_status, lv_color_hex(theme::FAIL), 0);
 #if defined(SEEED_WIO_TRACKER_L2)
     snprintf(used, sizeof(used), "Nothing from the receiver (%lu B)", (unsigned long)gps.rxChars());
@@ -342,10 +342,10 @@ void UITask::refreshGps() {
     for (int i = 0; i < s_n; i++) { if (s_sats[i].snr >= 0) tracked++; if (s_used_flag[i]) used_n++; }
     fix = g->hasFix();
     if (fix) {
-      lv_label_set_text(s_status, g->fix_mode == 2 ? "2D fix" : "3D fix");
+      setText(s_status, g->fix_mode == 2 ? "2D fix" : "3D fix");
       lv_obj_set_style_text_color(s_status, lv_color_hex(theme::OK), 0);
     } else {
-      lv_label_set_text(s_status, "Searching");
+      setText(s_status, "Searching");
       lv_obj_set_style_text_color(s_status, lv_color_hex(theme::ACCENT), 0);
     }
     snprintf(used, sizeof(used), "%d of %d used", fix ? (used_n ? used_n : g->sats_used) : 0, s_n);
@@ -362,7 +362,7 @@ void UITask::refreshGps() {
     }
     if (fix && g->hdop > 0) snprintf(dop, sizeof(dop), "H %.1f  V %.1f  P %.1f", g->hdop, g->vdop, g->pdop);
   }
-  lv_label_set_text(s_used, used);
+  setText(s_used, used);
   infoSet(s_inview, inview);
   infoSet(s_search, search);
   infoSet(s_ttff, ttff);
@@ -378,7 +378,7 @@ void UITask::refreshGps() {
     int n = 0, u = 0;
     for (int i = 0; i < s_n; i++) if (s_sats[i].sys == k) { n++; if (s_used_flag[i]) u++; }
     if (!n) { lv_obj_add_flag(s_sys_pill[k], LV_OBJ_FLAG_HIDDEN); continue; }
-    lv_label_set_text_fmt(s_sys_pill[k], "%c  %s  %d/%d", GpsSky::sysLetter(k), GpsSky::sysName(k), u, n);
+    setTextFmt(s_sys_pill[k], "%c  %s  %d/%d", GpsSky::sysLetter(k), GpsSky::sysName(k), u, n);
     lv_obj_remove_flag(s_sys_pill[k], LV_OBJ_FLAG_HIDDEN);
   }
 

examples/companion_radio/ui-lvgl/HomeScreen.h

@@ -729,7 +729,7 @@ void UITask::homeMapLayout() {
   }
   const char* hint = !mapview::s_available ? "No map on the SD card"
                    : !shown && !s_pending ? "No map tiles for this area" : nullptr;
-  if (hint) { lv_label_set_text(s_hint, hint); lv_obj_remove_flag(s_hint, LV_OBJ_FLAG_HIDDEN); }
+  if (hint) { setText(s_hint, hint); lv_obj_remove_flag(s_hint, LV_OBJ_FLAG_HIDDEN); }
   else lv_obj_add_flag(s_hint, LV_OBJ_FLAG_HIDDEN);
 }
 
@@ -786,14 +786,14 @@ void UITask::refreshHome() {
   if (known) {
     char date[48];
     fmtDate(date, sizeof(date), ti);
-    lv_label_set_text(_home_date, date);
+    setText(_home_date, date);
   } else {
-    lv_label_set_text(_home_date, "time not synced");
+    setText(_home_date, "time not synced");
   }
   for (int i = 0; i < FIELDS; i++) {
     if (!s_field_val[i] || !_prefs) continue;
     char v[24];
     homeFieldText(_prefs->dashboard_fields[i], v, sizeof(v));
-    lv_label_set_text(s_field_val[i], v);
+    setText(s_field_val[i], v);
   }
 }

examples/companion_radio/ui-lvgl/LvglPort.h

@@ -101,6 +101,19 @@ static lgfx::LGFX_Device* s_gfx = nullptr;
 static bool s_swallow = false;   // ignore the touch that woke the display until it lifts
 static uint32_t s_flush_us = 0;  // UI_PERF_TEST: time spent in flushCb
 
+// The CPU clock down to 80 MHz (LoRa, BLE and WiFi all run at that) with the
+// screen off (powerSave()), and with it on while nobody touches it and nothing
+// moves (the loop decides); a touch brings the full clock back before the
+// frame it causes is drawn.
+static uint32_t s_full_mhz = 0;
+static bool s_cpu_slow = false;
+static void cpuSlow(bool on) {
+  if (on == s_cpu_slow) return;
+  if (!s_full_mhz) s_full_mhz = getCpuFrequencyMhz();
+  s_cpu_slow = on;
+  setCpuFrequencyMhz(on ? 80 : s_full_mhz);
+}
+
 static void flushCb(lv_display_t* disp, const lv_area_t* area, uint8_t* px_map) {
 #ifdef UI_PERF_TEST
   uint32_t t = micros();
@@ -128,6 +141,7 @@ static void touchCb(lv_indev_t* indev, lv_indev_data_t* data) {
     return;
   }
   if (down) {
+    cpuSlow(false);   // the frame this touch causes: at the full clock
     data->state = LV_INDEV_STATE_PRESSED;
     data->point.x = tp.x;
     data->point.y = tp.y;
@@ -139,6 +153,7 @@ static void touchCb(lv_indev_t* indev, lv_indev_data_t* data) {
 static bool begin() {
   s_gfx = display.lgfxDevice();
   s_gfx->setColorDepth(16);
+  display.releaseFrameBuffer();
 
   lv_display_t* disp = lv_display_create(s_gfx->width(), s_gfx->height());
   lv_display_set_flush_cb(disp, flushCb);
@@ -169,19 +184,22 @@ static bool touched() {
 static void swallowTouch() { s_swallow = true; }
 
 // ── Power ────────────────────────────────────────────────────────────────────
-// Screen off: the CPU clock down (LoRa, BLE and WiFi all run at 80 MHz) and
+// Screen off: the clock down and the touch panel asleep unless a tap is to
-// the touch panel asleep unless a tap is to wake the screen. Screen on: back.
+// wake the screen. Screen on: back.
 static bool s_touch_asleep = false;
 static void powerSave(bool on, bool keep_touch) {
-  static uint32_t full_mhz = 0;
+  cpuSlow(on);
-  if (!full_mhz) full_mhz = getCpuFrequencyMhz();
-  setCpuFrequencyMhz(on ? 80 : full_mhz);
   if (on && !keep_touch) { board.touchSleep(); s_touch_asleep = true; }
   else if (!on && s_touch_asleep) { board.touchWake(); s_touch_asleep = false; }
 }
 // Nothing due for `ms`: the loop task blocks and the core idles, clock-gated,
-// instead of spinning.
+// instead of spinning -- woken early by a frame from the app (below).
-static void idle(uint32_t ms) { if (ms) vTaskDelay(pdMS_TO_TICKS(ms)); }
+static TaskHandle_t s_loop_task = nullptr;
+static void idle(uint32_t ms) {
+  if (!ms) return;
+  if (!s_loop_task) s_loop_task = xTaskGetCurrentTaskHandle();
+  ulTaskNotifyTake(pdTRUE, pdMS_TO_TICKS(ms));
+}
 
 // Backlight 1-100 % (the brightness slider), on the LP5814 PWM.
 static void setBacklightPct(uint8_t pct) {
@@ -496,10 +514,12 @@ static int netState() {
     default:                return NET_CONNECTING;
   }
 }
+static void fetchFreeBuffer();
 static void netEnd() {
   if (s_net_scanning) { s_net_scanning = false; WiFi.scanDelete(); }
   WiFi.disconnect(true);
   WiFi.mode(WIFI_OFF);
+  fetchFreeBuffer();
 }
 // The network joined (Settings > WiFi marks it), "" when not connected.
 static void netSsid(char* out, size_t n) {
@@ -651,6 +671,14 @@ static void fetchAbandon() {
   else fetchRelease();
 }
 static const char* fetchError() { return s_ferr; }
+// WiFi off: the response buffer (grown to the biggest tile or update chunk,
+// up to 512 KB of PSRAM) given back, unless a request is still finishing.
+static void fetchFreeBuffer() {
+  if (s_fstate != F_IDLE) return;
+  heap_caps_free(s_fbuf);
+  s_fbuf = nullptr;
+  s_fcap = s_flen = 0;
+}
 
 #elif defined(SIM_PLATFORM) && defined(__EMSCRIPTEN__)
 // Browser simulator (variants/sim/build_wasm_lvgl.sh): SimLcdDisplay blits to
@@ -719,6 +747,7 @@ static bool begin() {
 static bool touched() { return SimLcdDisplay::touchState().down; }
 static void swallowTouch() { s_swallow = true; }
 static void powerSave(bool, bool) {}   // the browser's page loop runs the sim
+static void cpuSlow(bool) {}
 static void idle(uint32_t) {}
 static void setBacklightPct(uint8_t pct) { (void)pct; }   // the browser canvas has no backlight
 
@@ -870,3 +899,11 @@ static void loadHomeApps(char* out, size_t n) { nvs::getStr("mc_ui", "apps", out
 static void saveHomeApps(const char* v) { nvs::putStr("mc_ui", "apps", v); }
 
 }  // namespace lvport
+
+#if defined(SEEED_WIO_TRACKER_L2)
+// A frame from the app (SerialBLEInterface, the BLE stack's task): the loop,
+// blocked in lvport::idle(), reads it now rather than at the next timeout.
+void serialFrameArrived() {
+  if (TaskHandle_t t = lvport::s_loop_task) xTaskNotifyGive(t);
+}
+#endif

examples/companion_radio/ui-lvgl/MapScreen.h

@@ -116,11 +116,12 @@ static void drawGrid(lv_event_t* e) {
 // Markers, remembered so layout can reposition them. `idx` is the Nearby row
 // (MK_NODE), the waypoint index (MK_WAYPOINT) or the live-share slot (MK_LIVE).
 enum : uint8_t { MK_NODE, MK_WAYPOINT, MK_LIVE };
-struct Mark { int32_t lat_e6, lon_e6; int idx; uint8_t kind; lv_obj_t* obj; lv_obj_t* dot; };
+struct Mark { int32_t lat_e6, lon_e6; int idx; uint8_t kind; uint32_t col, text_hash; lv_obj_t* obj; lv_obj_t* dot; };
 static const int MAX_MARKS = NearbyModel::MAX_NEARBY > WaypointStore::CAPACITY + LiveTrackStore::CAPACITY
                              ? NearbyModel::MAX_NEARBY : WaypointStore::CAPACITY + LiveTrackStore::CAPACITY;   // Nearby map, or waypoints + live shares
 static Mark* s_marks = psramBuf<Mark>(MAX_MARKS);
 static int  s_mark_count = 0;
+static int  s_mark_prev = 0;   // during a rebuild: how many the last one left, reused where unchanged
 static int  s_drag = 0;   // px moved in the current press: a drag isn't a tap
 static bool s_available = false;   // provider has data; checked when the map opens, not per frame
 static double s_left = 0, s_top = 0;   // world px (at the current zoom) of the view's top-left
@@ -419,7 +420,7 @@ void UITask::layoutMap() {
     double lat = atan(sinh(M_PI * (1 - 2 * _map_cy / (double)(1 << _map_z)))) * 180.0 / M_PI;
     mapview::s_grid = { left, top, mapview::gridStep(_map_z, lat, _prefs && _prefs->units_imperial, 56, sl, sizeof(sl)) };
     if (mapview::s_scale_lbl) {
-      lv_label_set_text(mapview::s_scale_lbl, sl);
+      setText(mapview::s_scale_lbl, sl);
       lv_obj_set_width(mapview::s_scale_bar, (int)lround(mapview::s_grid.step_px));
     }
     lv_obj_invalidate(_map_area);
@@ -494,20 +495,20 @@ void UITask::layoutMap() {
   }
   if (_map_nav) layoutNav();
 
-  if (over) lv_label_set_text_fmt(_map_zoom_lbl, "z%d  (map z%d)", _map_z, _map_z - over);   // magnified
+  if (over) setTextFmt(_map_zoom_lbl, "z%d  (map z%d)", _map_z, _map_z - over);   // magnified
   else if (mapview::s_provider == &mapview::s_vector)   // spike: how long a tile takes
   {
     uint32_t ld, fl, ln;
     mapview::s_vector.lastSplit(ld, fl, ln);
-    lv_label_set_text_fmt(_map_zoom_lbl, "z%d  vt %lu ms (r%lu a%lu l%lu)", _map_z, (unsigned long)mapview::s_vector.lastMs(),
+    setTextFmt(_map_zoom_lbl, "z%d  vt %lu ms (r%lu a%lu l%lu)", _map_z, (unsigned long)mapview::s_vector.lastMs(),
                           (unsigned long)ld, (unsigned long)fl, (unsigned long)ln);
   }
-  else lv_label_set_text_fmt(_map_zoom_lbl, "z%d", _map_z);
+  else setTextFmt(_map_zoom_lbl, "z%d", _map_z);
   const char* hint = !have_provider ? "No map on the SD card.\nPut tiles in /maps (tools/maps)."
                    : mapview::s_dl.liveQueued() > 0 ? nullptr   // being fetched
                    : (!_map_pending && shown == 0 && missing > 0)
                        ? "No map here at this zoom -\nzoom out or download the area" : nullptr;
-  if (hint && !areaSelecting()) { lv_label_set_text(_map_hint, hint); lv_obj_remove_flag(_map_hint, LV_OBJ_FLAG_HIDDEN); }
+  if (hint && !areaSelecting()) { setText(_map_hint, hint); lv_obj_remove_flag(_map_hint, LV_OBJ_FLAG_HIDDEN); }
   else lv_obj_add_flag(_map_hint, LV_OBJ_FLAG_HIDDEN);
   areaLayout();
 }
@@ -585,10 +586,12 @@ void UITask::mapLoop() {
 
 void UITask::rebuildMapMarkers() {
   if (!_map_marks) return;
-  for (int k = 0; k < mapview::s_mark_count; k++) lv_obj_delete(mapview::s_marks[k].obj);
+  mapview::s_mark_prev = mapview::s_mark_count;
   mapview::s_mark_count = 0;
   if (_map_nav) rebuildNavMarkers();
   else rebuildNodeMarkers();
+  for (int k = mapview::s_mark_count; k < mapview::s_mark_prev; k++) lv_obj_delete(mapview::s_marks[k].obj);
+  mapview::s_mark_prev = 0;
   lv_obj_update_layout(_map_marks);   // so layoutMap() knows where each dot sits in its marker
 }
 
@@ -604,9 +607,22 @@ void UITask::rebuildNodeMarkers() {
 
 // One clickable object per marker: a dot plus the name beside it. The object
 // is placed so the dot's centre is on the spot, from where layout actually put
-// the dot inside it (Mark::dot) -- the name may be taller than the dot.
+// the dot inside it (Mark::dot) -- the name may be taller than the dot. The
+// markers are rebuilt every few seconds: one the same as the last time in its
+// slot is kept as it is, so an unchanged map isn't redrawn under it.
 void UITask::addMapMark(uint8_t kind, int idx, int32_t lat_e6, int32_t lon_e6, uint32_t col, const char* text) {
   if (!_map_marks || mapview::s_mark_count >= mapview::MAX_MARKS) return;
+  uint32_t h = 2166136261u;   // FNV-1a of the name
+  for (const char* c = text; *c; c++) h = (h ^ (uint8_t)*c) * 16777619u;
+  int k = mapview::s_mark_count;
+  if (k < mapview::s_mark_prev) {
+    mapview::Mark& old = mapview::s_marks[k];
+    if (old.kind == kind && old.idx == idx && old.lat_e6 == lat_e6 && old.lon_e6 == lon_e6 && old.col == col && old.text_hash == h) {
+      mapview::s_mark_count++;
+      return;
+    }
+    lv_obj_delete(old.obj);
+  }
   lv_obj_t* m = lv_obj_create(_map_marks);
   lv_obj_remove_style_all(m);
   lv_obj_set_size(m, LV_SIZE_CONTENT, LV_SIZE_CONTENT);
@@ -628,7 +644,7 @@ void UITask::addMapMark(uint8_t kind, int idx, int32_t lat_e6, int32_t lon_e6, u
   lv_obj_remove_flag(name, LV_OBJ_FLAG_CLICKABLE);
 
   mapview::Mark& mk = mapview::s_marks[mapview::s_mark_count++];
-  mk.lat_e6 = lat_e6; mk.lon_e6 = lon_e6; mk.idx = idx; mk.kind = kind; mk.obj = m; mk.dot = dot;
+  mk.lat_e6 = lat_e6; mk.lon_e6 = lon_e6; mk.idx = idx; mk.kind = kind; mk.col = col; mk.text_hash = h; mk.obj = m; mk.dot = dot;
 }
 
 void UITask::mapPan(int dx, int dy) {
@@ -968,24 +984,24 @@ void UITask::mapDownloadTick() {
   next_ui = millis() + 500;
   if (_map_dl_pill) {
     if (dl.state() == mapview::TileDownloader::CONNECTING) {
-      lv_label_set_text(_map_dl_pill, LV_SYMBOL_WIFI " Connecting...");
+      setText(_map_dl_pill, LV_SYMBOL_WIFI " Connecting...");
       lv_obj_remove_flag(_map_dl_pill, LV_OBJ_FLAG_HIDDEN);
     } else if (dl.active()) {
       if (dl.failed())
-        lv_label_set_text_fmt(_map_dl_pill, LV_SYMBOL_DOWNLOAD " %lu / %lu  " LV_SYMBOL_WARNING " %lu",
+        setTextFmt(_map_dl_pill, LV_SYMBOL_DOWNLOAD " %lu / %lu  " LV_SYMBOL_WARNING " %lu",
                               (unsigned long)dl.processed(), (unsigned long)dl.total(), (unsigned long)dl.failed());
       else
-        lv_label_set_text_fmt(_map_dl_pill, LV_SYMBOL_DOWNLOAD " %lu / %lu", (unsigned long)dl.processed(),
+        setTextFmt(_map_dl_pill, LV_SYMBOL_DOWNLOAD " %lu / %lu", (unsigned long)dl.processed(),
                               (unsigned long)dl.total());
       lv_obj_remove_flag(_map_dl_pill, LV_OBJ_FLAG_HIDDEN);
     } else if (dl.liveConnecting()) {
-      lv_label_set_text(_map_dl_pill, LV_SYMBOL_WIFI " Connecting...");
+      setText(_map_dl_pill, LV_SYMBOL_WIFI " Connecting...");
       lv_obj_remove_flag(_map_dl_pill, LV_OBJ_FLAG_HIDDEN);
     } else if (dl.liveQueued() > 0) {
-      lv_label_set_text_fmt(_map_dl_pill, LV_SYMBOL_DOWNLOAD " live %d", dl.liveQueued());
+      setTextFmt(_map_dl_pill, LV_SYMBOL_DOWNLOAD " live %d", dl.liveQueued());
       lv_obj_remove_flag(_map_dl_pill, LV_OBJ_FLAG_HIDDEN);
     } else if (mapview::s_available && dl.savedJob(s_job_tmp)) {
-      lv_label_set_text(_map_dl_pill, LV_SYMBOL_DOWNLOAD " Resume?");
+      setText(_map_dl_pill, LV_SYMBOL_DOWNLOAD " Resume?");
       lv_obj_remove_flag(_map_dl_pill, LV_OBJ_FLAG_HIDDEN);
     } else {
       lv_obj_add_flag(_map_dl_pill, LV_OBJ_FLAG_HIDDEN);

examples/companion_radio/ui-lvgl/NavMap.h

@@ -290,7 +290,7 @@ void UITask::refreshNavBar() {
       navmap::fmtDuration(left, sizeof(left), _core->live_share.remainingSecs());
       o += snprintf(t + o, sizeof(t) - o, "%sLIVE %s", o ? "  " : "", left);
     }
-    lv_label_set_text(_nav_rec, t);
+    setText(_nav_rec, t);
     if (o) lv_obj_remove_flag(_nav_rec, LV_OBJ_FLAG_HIDDEN); else lv_obj_add_flag(_nav_rec, LV_OBJ_FLAG_HIDDEN);
   }
   int32_t tlat, tlon;
@@ -298,23 +298,23 @@ void UITask::refreshNavBar() {
   bool person = false, set = false;
   bool pos = navCurrentTarget(tlat, tlon, name, sizeof(name), person, set);
   if (!set) {
-    lv_label_set_text(_nav_title, "No target");
+    setText(_nav_title, "No target");
     lv_obj_set_style_text_color(_nav_title, lv_color_hex(theme::TEXT_MUTED), 0);
-    lv_label_set_text(_nav_info, "Tap here to pick a target, or hold the map on a spot");
+    setText(_nav_info, "Tap here to pick a target, or hold the map on a spot");
     lv_obj_add_flag(_nav_clear, LV_OBJ_FLAG_HIDDEN);
     return;
   }
   lv_obj_set_style_text_color(_nav_title, lv_color_hex(theme::ACCENT), 0);
   lv_obj_remove_flag(_nav_clear, LV_OBJ_FLAG_HIDDEN);
-  lv_label_set_text_fmt(_nav_title, "%s %s", navmap::s_tb.active() ? LV_SYMBOL_LOOP : person ? UI_SYMBOL_USERS : UI_SYMBOL_FLAG,
+  setTextFmt(_nav_title, "%s %s", navmap::s_tb.active() ? LV_SYMBOL_LOOP : person ? UI_SYMBOL_USERS : UI_SYMBOL_FLAG,
                         name);
   if (!pos) {
-    lv_label_set_text(_nav_info, "Position unknown (not shared recently)");
+    setText(_nav_info, "Position unknown (not shared recently)");
     return;
   }
   int32_t lat, lon;
   if (!_core->course.currentLocation(lat, lon)) {
-    lv_label_set_text(_nav_info, _core->gpsEnabled() || !_core->gpsAvailable()
+    setText(_nav_info, _core->gpsEnabled() || !_core->gpsAvailable()
                                  ? "Waiting for a GPS fix..." : "GPS is off  -  tap the crosshair to turn it on");
     return;
   }
@@ -327,9 +327,9 @@ void UITask::refreshNavBar() {
   int cog;
   if (_core->course.currentCourse(cog)) snprintf(hdg, sizeof(hdg), "  -  you %d\xC2\xB0", cog);
   if (navmap::s_eta.eta(km, eta, sizeof(eta)))
-    lv_label_set_text_fmt(_nav_info, "%s  %d\xC2\xB0 %s%s  -  ETA %s", dist, to, geo::bearingCardinal(to), hdg, eta);
+    setTextFmt(_nav_info, "%s  %d\xC2\xB0 %s%s  -  ETA %s", dist, to, geo::bearingCardinal(to), hdg, eta);
   else
-    lv_label_set_text_fmt(_nav_info, "%s  %d\xC2\xB0 %s%s", dist, to, geo::bearingCardinal(to), hdg);
+    setTextFmt(_nav_info, "%s  %d\xC2\xB0 %s%s", dist, to, geo::bearingCardinal(to), hdg);
 }
 
 // ── Target selection ──────────────────────────────────────────────────────────

examples/companion_radio/ui-lvgl/SoundScreen.h

@@ -350,7 +350,7 @@ void UITask::refreshMelody() {
   lightNote(s_play_all ? melodyNote() : -1);
   if (!s_play_lbl || playing == s_playing_shown) return;
   s_playing_shown = playing;
-  lv_label_set_text(s_play_lbl, playing ? LV_SYMBOL_STOP "  Stop" : LV_SYMBOL_PLAY "  Play");
+  setText(s_play_lbl, playing ? LV_SYMBOL_STOP "  Stop" : LV_SYMBOL_PLAY "  Play");
 }
 
 void UITask::melodySave() {

examples/companion_radio/ui-lvgl/StorageScreen.h

@@ -313,7 +313,7 @@ void UITask::pollStorage() {
   if (s_sd_bar && !s_sd_read) {
     s_sd_read = true;
     s_sd_ok = lvport::sdInfo(s_sd_total, s_sd_used, s_sd_card);
-    if (!s_sd_ok) lv_label_set_text(s_sd_lbl, "Can't read the card");
+    if (!s_sd_ok) setText(s_sd_lbl, "Can't read the card");
     else if (s_sd_card > s_sd_total + s_sd_total / 4) {   // most of the card sits outside the partition
       char c[16], t[16], line[160];
       fmtBytes(c, sizeof(c), s_sd_card);
@@ -337,7 +337,7 @@ void UITask::pollStorage() {
     fmtBytes(b, sizeof(b), mapview::s_live_cache.bytes());
     if (mapview::s_live_cache.clearing()) snprintf(t, sizeof(t), "Deleting... %lu left", (unsigned long)mapview::s_live_cache.count());
     else snprintf(t, sizeof(t), "%lu tiles, %s", (unsigned long)mapview::s_live_cache.count(), b);
-    lv_label_set_text(s_live_info, t);
+    setText(s_live_info, t);
   }
 }
 

examples/companion_radio/ui-lvgl/UITask.cpp

@@ -133,6 +133,23 @@ static lv_obj_t* label(lv_obj_t* parent, const char* text, const lv_font_t* font
   lv_obj_set_style_text_color(l, lv_color_hex(color), 0);
   return l;
 }
+// A label's text, set only when it differs: LVGL redraws a label on every
+// set_text, the same text or not, and the refreshes that run every second
+// mostly write back what's already there.
+static void setText(lv_obj_t* l, const char* text) {
+  const char* cur = lv_label_get_text(l);
+  if (cur && strcmp(cur, text) == 0) return;
+  lv_label_set_text(l, text);
+}
+static void setTextFmt(lv_obj_t* l, const char* fmt, ...) __attribute__((format(printf, 2, 3)));
+static void setTextFmt(lv_obj_t* l, const char* fmt, ...) {
+  char b[160];
+  va_list ap;
+  va_start(ap, fmt);
+  vsnprintf(b, sizeof(b), fmt, ap);
+  va_end(ap);
+  setText(l, b);
+}
 // A sentence across the parent's width, wrapping: a hint, a note, a status.
 static lv_obj_t* noteLabel(lv_obj_t* parent, const char* text, const lv_font_t* font = THEME_FONT_SMALL,
                            uint32_t color = theme::TEXT_MUTED) {
@@ -296,7 +313,7 @@ static void infoSet(lv_obj_t* value, const char* text) {
   lv_obj_t* row = lv_obj_get_parent(value);
   if (!text || !text[0]) { lv_obj_add_flag(row, LV_OBJ_FLAG_HIDDEN); return; }
   lv_obj_remove_flag(row, LV_OBJ_FLAG_HIDDEN);
-  lv_label_set_text(value, text);
+  setText(value, text);
 }
 
 // A bare flex row / column sized to its content, taps passing through.
@@ -828,9 +845,9 @@ static void clockFaceSet(lv_obj_t* f, const struct tm* ti, const NodePrefs* p) {
   lv_obj_t* ap = lv_obj_get_child(f, 1);
   char clk[12] = "--:--";
   if (ti) fmtClock(clk, sizeof(clk), *ti, p, false, true);
-  lv_label_set_text(lv_obj_get_child(f, 0), clk);
+  setText(lv_obj_get_child(f, 0), clk);
   bool h12 = ti && p && p->clock_12h;
-  if (h12) lv_label_set_text(ap, ti->tm_hour < 12 ? "AM" : "PM");
+  if (h12) setText(ap, ti->tm_hour < 12 ? "AM" : "PM");
   if (h12 != !lv_obj_has_flag(ap, LV_OBJ_FLAG_HIDDEN)) {
     if (h12) lv_obj_remove_flag(ap, LV_OBJ_FLAG_HIDDEN);
     else lv_obj_add_flag(ap, LV_OBJ_FLAG_HIDDEN);
@@ -1110,6 +1127,7 @@ void UITask::loop() {
       uint32_t sig = threadSignature();
       if (_thread_dirty || sig != _thread_sig) refreshThread();
     }
+    lvport::cpuSlow(!cpuNeeded());
     lv_next = lv_timer_handler();
   }
   lvport::idle(idleMillis(lv_next));
@@ -1117,13 +1135,14 @@ void UITask::loop() {
 
 // How long loop() may sleep: nothing is due before then. Not at all while the
 // mesh has packets queued; briefly while a melody plays (its notes are timed
-// here) or the app is connected (its frames are read one a pass).
+// here) or frames to or from the app wait (read one a pass, sent spaced out).
+// A frame arriving from the app over BLE wakes the loop (serialFrameArrived).
 uint32_t UITask::idleMillis(uint32_t lv_next) {
   if (the_mesh.hasPendingWork()) return 0;
 #ifdef PIN_BUZZER
   if (_buzzer.isPlaying()) return 1;
 #endif
-  if (isClientConnected()) return 2;
+  if (isClientConnected() && _serial->hasPendingFrames()) return 2;
   if (_asleep) return 50;   // as often as the buttons and tap to wake are polled
   return lv_next < 10 ? lv_next : 10;   // LVGL's next timer: a refresh, an animation, input
 }
@@ -1429,9 +1448,9 @@ void UITask::refreshStatusBar() {
   if (localTime(_prefs, ti)) {
     char clk[12];
     fmtClock(clk, sizeof(clk), ti, _prefs, true);
-    lv_label_set_text(_status_time, clk);
+    setText(_status_time, clk);
   } else {
-    lv_label_set_text(_status_time, "--:--");
+    setText(_status_time, "--:--");
   }
 
   // Battery: the icon, then % or volts per Settings > Battery display. The
@@ -1446,7 +1465,7 @@ void UITask::refreshStatusBar() {
     case battery::VOLTAGE: snprintf(level, sizeof(level), " %u.%02u V", mv / 1000, (mv % 1000) / 10); break;
     default: break;
   }
-  lv_label_set_text_fmt(_status_batt, "%s%s", batt, level);
+  setTextFmt(_status_batt, "%s%s", batt, level);
   lv_obj_t* left_of = _status_batt;   // the icons pack up to this
   if (_board->isExternalPowered()) {
     lv_obj_remove_flag(_status_chg, LV_OBJ_FLAG_HIDDEN);
@@ -2246,8 +2265,8 @@ void UITask::refreshScanPopup() {
   if (!_scan_list) return;
   _scan->refreshScan();
   int n = _scan->count();
-  if (_scanning) lv_label_set_text_fmt(_scan_status, LV_SYMBOL_REFRESH "  Listening for replies... %d", n);
+  if (_scanning) setTextFmt(_scan_status, LV_SYMBOL_REFRESH "  Listening for replies... %d", n);
-  else lv_label_set_text_fmt(_scan_status, "%d node%s answered the discover request", n, n == 1 ? "" : "s");
+  else setTextFmt(_scan_status, "%d node%s answered the discover request", n, n == 1 ? "" : "s");
 
   uint32_t sig = (uint32_t)n + (_scanning ? 0x10000u : 0);
   for (int i = 0; i < n; i++) {
@@ -2309,10 +2328,10 @@ void UITask::refreshNearbyList() {
   int n = _nearby->count();
 
   if (_nearby_sort_lbl)
-    lv_label_set_text(_nearby_sort_lbl, _nearby->sortMode() == NearbyModel::SORT_TIME ? "Recent" : "Dist");
+    setText(_nearby_sort_lbl, _nearby->sortMode() == NearbyModel::SORT_TIME ? "Recent" : "Dist");
   int32_t lat, lon;
   bool gps = _nearby->ownPosition(lat, lon);
-  lv_label_set_text_fmt(_nearby_status, "%d node%s%s", n, n == 1 ? "" : "s",
+  setTextFmt(_nearby_status, "%d node%s%s", n, n == 1 ? "" : "s",
                         gps ? "" : "  -  no GPS fix, distances unknown");
   if (sig == _nearby_sig) return;
   _nearby_sig = sig;
@@ -2455,12 +2474,12 @@ void UITask::refreshNode() {
     int16_t out = 0, back = 0; uint32_t rtt = 0;
     _core->ping.getResult(out, back, rtt);
     if (!_core->ping.isActive() && (out || back || rtt)) {
-      lv_label_set_text_fmt(_node_ping, "Ping %lu ms  -  SNR out %.1f  back %.1f", (unsigned long)rtt,
+      setTextFmt(_node_ping, "Ping %lu ms  -  SNR out %.1f  back %.1f", (unsigned long)rtt,
                             out / 4.0f, back / 4.0f);
       _pinging = false;
     } else if (millis() - _ping_started_ms > 3000) {
       _core->ping.clear();
-      lv_label_set_text(_node_ping, "Ping: no reply");
+      setText(_node_ping, "Ping: no reply");
       _pinging = false;
     }
   }
@@ -3459,6 +3478,19 @@ void UITask::setKeyboardAlphabets(int main_idx, int alt_sel) {
 #include "StorageScreen.h"
 #include "Splash.h"
 
+// The screen on, the full CPU clock while it's worth having: touched in the
+// last CPU_IDLE_MS, something moving, map tiles to decode, a download or an
+// update on WiFi. Otherwise 80 MHz (lvport::cpuSlow) -- a clock ticking over,
+// a message being read.
+static constexpr uint32_t CPU_IDLE_MS = 2000;
+bool UITask::cpuNeeded() {
+  if (lv_display_get_inactive_time(NULL) < CPU_IDLE_MS || lv_anim_count_running() > 0) return true;
+  if (wifiInUse() || mapview::s_dl.liveQueued() > 0) return true;
+  if (_screen == SCR_MAP && _map_pending) return true;
+  if (_screen == SCR_HOME && home::mini::s_area && home::mini::s_pending) return true;
+  return false;
+}
+
 #if defined(SIM_PLATFORM) && defined(__EMSCRIPTEN__)
 // Sim tests: straight to a screen by name.
 extern "C" EMSCRIPTEN_KEEPALIVE void sim_open(const char* name) {

examples/companion_radio/ui-lvgl/UITask.h

@@ -419,6 +419,7 @@ private:
   bool _wake_down = false;
   uint32_t autoOffMillis() const;
   uint32_t idleMillis(uint32_t lv_next);
+  bool cpuNeeded();
   void checkLowBattery();
 
 #ifdef PIN_BUZZER

examples/companion_radio/ui-lvgl/WifiScreen.h

@@ -269,7 +269,7 @@ void UITask::pollWifiScan() {
     lv_obj_center(label(b, text, THEME_FONT_SMALL, known ? theme::ACCENT : theme::TEXT));
   }
   if (n > 0) lv_obj_remove_flag(_wifi_list, LV_OBJ_FLAG_HIDDEN);
-  lv_label_set_text(_wifi_status, n > 0 ? "Tap a network, then enter its password." : "No networks found.");
+  setText(_wifi_status, n > 0 ? "Tap a network, then enter its password." : "No networks found.");
   if (!wifiInUse()) lvport::netEnd();   // the scan switched the radio on
 }
 

src/helpers/BaseSerialInterface.h

@@ -25,6 +25,10 @@ public:
   // isConnected() so single-transport interfaces are unchanged.
   virtual bool isClientConnected() const { return isConnected(); }
 
+  // For a loop that sleeps between passes: frames waiting to be read or sent.
+  // An interface that can't tell says true (poll it often).
+  virtual bool hasPendingFrames() const { return true; }
+
   virtual bool isWriteBusy() const = 0;
   virtual size_t writeFrame(const uint8_t src[], size_t len) = 0;
   virtual size_t checkRecvFrame(uint8_t dest[]) = 0;

src/helpers/esp32/DualSerialInterface.h

@@ -52,6 +52,11 @@ public:
   bool isClientConnected() const override { return isBLEConnected(); }
 #endif
 
+  // USB can't tell without reading it.
+  bool hasPendingFrames() const override {
+    return (_ble_enabled && _ble.isConnected()) ? _ble.hasPendingFrames() : true;
+  }
+
   bool isWriteBusy() const override {
     return (_ble_enabled && _ble.isConnected()) ? _ble.isWriteBusy() : _usb.isWriteBusy();
   }

src/helpers/esp32/SerialBLEInterface.cpp

@@ -10,6 +10,8 @@
 
 #define ADVERT_RESTART_DELAY  1000   // millis
 
+__attribute__((weak)) void serialFrameArrived() {}
+
 // As the nRF52 interface: 20-30 ms for the first 30 s (the app finds it at
 // once), then 152.5 ms. Left alone, the library advertises every 30-60 ms
 // for as long as nothing is connected. Units of 0.625 ms.
@@ -187,6 +189,7 @@ void SerialBLEInterface::onWrite(BLECharacteristic* pCharacteristic, esp_ble_gat
     if (xQueueSend(recv_queue, &frame, 0) != pdTRUE) {
       BLE_DEBUG_PRINTLN("ERROR: onWrite(), recv_queue is full!");
     }
+    serialFrameArrived();
   }
 }
 

src/helpers/esp32/SerialBLEInterface.h

@@ -8,6 +8,10 @@
 #include <freertos/FreeRTOS.h>
 #include <freertos/queue.h>
 
+// A frame from the app was queued (the BLE stack's task). Weak, empty by
+// default: a firmware whose loop blocks between passes defines it to wake it.
+void serialFrameArrived();
+
 class SerialBLEInterface : public BaseSerialInterface, BLESecurityCallbacks, BLEServerCallbacks, BLECharacteristicCallbacks {
   BLEServer *pServer;
   BLEService *pService;
@@ -102,6 +106,7 @@ public:
 
   bool isConnected() const override;
 
+  bool hasPendingFrames() const override { return send_queue_len > 0 || uxQueueMessagesWaiting(recv_queue) > 0; }
   bool isWriteBusy() const override;
   size_t writeFrame(const uint8_t src[], size_t len) override;
   size_t checkRecvFrame(uint8_t dest[]) override;

variants/wio-tracker-l2/WioTrackerL2Display.h

@@ -182,6 +182,9 @@ public:
 
   // direct access to the LGFX device (LVGL flush/touch glue)
   lgfx::LGFX_Device* lgfxDevice() { return &disp; }
+  // LVGL draws straight to the panel: the frame sprite (76 KB of PSRAM) only
+  // carried the boot "Loading..." -- given back once LVGL takes over.
+  void releaseFrameBuffer() { buffer.deleteSprite(); }
 
   // reliable touch read in logical (UI_ZOOM-scaled) coords; returns false when
   // not touched (LGFXDisplay::getTouch reads an uninitialized point on release)