feat(power): battery saving — hardware duty-cycle RX + adaptive TX power

Two independent, default-off toggles under Settings › Radio.

Pwr save: hardware RX duty-cycle (SX126x SetRxDutyCycle via
startReceiveDutyCycleAuto). The chip cycles RX↔sleep and wakes on a preamble —
no MCU state machine; recvRaw reads the packet exactly as in continuous RX.
Falls back to continuous RX on non-SX126x. (Replaces an earlier software-CAD
state machine that fought the hardware: polling a warm-sleeping chip gave a
phantom-busy channel that stalled TX ~4 s and dropped ACKs in the scan gaps.)

Auto pwr: Adaptive Power Control. tx_power_dbm becomes a ceiling; actual TX
power tracks the reverse-link SNR margin (measured above the per-SF demod floor,
EWMA-smoothed, proportional step with a deadband). Feedback comes from direct /
room-server ACKs and, for channels (no ACK), from hearing a repeater rebroadcast
our own flood; a lost confirmation ramps power back up so channel sends can't get
stranded below what the repeaters can hear.

Prefs schema 0xC0DE0009 (rx_powersave, tx_apc). Radio page / name bar show the
live TX power; noise floor reads n/a while duty-cycling.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/companion_radio/ui-new/SettingsScreen.h

@@ -54,6 +54,8 @@ class SettingsScreen : public UIScreen {
     // Radio section
     SECTION_RADIO,
     TX_POWER,
+    POWER_SAVE,
+    TX_APC,
     // System section
     SECTION_SYSTEM,
     TIMEZONE,
@@ -479,6 +481,14 @@ class SettingsScreen : public UIScreen {
       snprintf(buf, sizeof(buf),"%ddBm", p ? p->tx_power_dbm : 0);
       display.setCursor(display.valCol(), y);
       display.print(buf);
+    } else if (item == POWER_SAVE) {
+      display.print("Pwr save");
+      display.setCursor(display.valCol(), y);
+      display.print((p && p->rx_powersave) ? "ON" : "OFF");
+    } else if (item == TX_APC) {
+      display.print("Auto pwr");
+      display.setCursor(display.valCol(), y);
+      display.print((p && p->tx_apc) ? "ON" : "OFF");
 #if AUTO_OFF_MILLIS > 0
     } else if (item == AUTO_OFF) {
       display.print("AutoOff");
@@ -736,6 +746,18 @@ public:
       if (right && p->tx_power_dbm < 22) { p->tx_power_dbm++; _task->applyTxPower(); _dirty = true; return true; }
       if (left  && p->tx_power_dbm > 2)  { p->tx_power_dbm--; _task->applyTxPower(); _dirty = true; return true; }
     }
+    if (_selected == POWER_SAVE && p && (left || right || enter)) {
+      p->rx_powersave ^= 1;
+      _task->applyPowerSave();
+      _dirty = true;
+      return true;
+    }
+    if (_selected == TX_APC && p && (left || right || enter)) {
+      p->tx_apc ^= 1;
+      _task->applyApc();
+      _dirty = true;
+      return true;
+    }
 #if AUTO_OFF_MILLIS > 0
     if (_selected == AUTO_OFF && p) {
       int idx = autoOffIndex();

examples/companion_radio/ui-new/UITask.cpp

@@ -555,7 +555,15 @@ public:
       display.translateUTF8ToBlocks(filtered_name, _node_prefs->node_name, sizeof(filtered_name));
       int rightEdge = renderBatteryIndicator(display, _task->getBattMilliVolts());
       display.setColor(DisplayDriver::LIGHT);
-      display.drawTextEllipsized(0, 0, rightEdge - 2, filtered_name);
+      if (_node_prefs && _node_prefs->tx_apc) {
+        char pwr_buf[8];
+        snprintf(pwr_buf, sizeof(pwr_buf), "%ddB", (int)radio_driver.getTxPower());
+        int pwr_w = display.getTextWidth(pwr_buf);
+        display.drawTextEllipsized(0, 0, rightEdge - 2 - pwr_w - 2, filtered_name);
+        display.drawTextRightAlign(rightEdge - 2, 0, pwr_buf);
+      } else {
+        display.drawTextEllipsized(0, 0, rightEdge - 2, filtered_name);
+      }
     }
 
     // ensure current page is visible (e.g. after settings change)
@@ -729,10 +737,14 @@ public:
 
       // tx power, noise floor
       display.setCursor(0, content_y + step * 2);
-      snprintf(tmp, sizeof(tmp),"TX: %ddBm", _node_prefs->tx_power_dbm);
+      snprintf(tmp, sizeof(tmp),"TX: %ddBm", radio_driver.getTxPower());   // live value (reflects APC)
       display.print(tmp);
       display.setCursor(0, content_y + step * 3);
-      snprintf(tmp, sizeof(tmp),"Noise floor: %d", radio_driver.getNoiseFloor());
+      if (radio_driver.getPowerSaving()) {   // duty-cycle RX doesn't sample the floor
+        snprintf(tmp, sizeof(tmp),"Noise floor: n/a");
+      } else {
+        snprintf(tmp, sizeof(tmp),"Noise floor: %d", radio_driver.getNoiseFloor());
+      }
       display.print(tmp);
     } else if (_page == HomePage::BLUETOOTH) {
       display.setColor(DisplayDriver::LIGHT);
@@ -2063,9 +2075,21 @@ void UITask::toggleGPS() {
 
 void UITask::applyTxPower() {
   if (_node_prefs == NULL) return;
+  // With APC on, tx_power_dbm is the ceiling — re-baseline the controller to it
+  // (which also sets the radio) so the live power tracks the new ceiling at once.
+  if (_node_prefs->tx_apc) { the_mesh.applyApc(); return; }
   radio_driver.setTxPower(_node_prefs->tx_power_dbm);
 }
 
+void UITask::applyPowerSave() {
+  if (_node_prefs == NULL) return;
+  radio_driver.setPowerSaving(_node_prefs->rx_powersave);
+}
+
+void UITask::applyApc() {
+  the_mesh.applyApc();   // (re)initialise Adaptive Power Control from prefs
+}
+
 void UITask::applyBrightness() {
   if (_display != NULL && _node_prefs != NULL) {
     _display->setBrightness(_node_prefs->display_brightness);

examples/companion_radio/ui-new/UITask.h

@@ -249,6 +249,8 @@ public:
   void setBuzzerVolumeLevel(uint8_t level);
   uint8_t getBuzzerVolume() const { return _node_prefs ? _node_prefs->buzzer_volume : 4; }
   void applyTxPower();
+  void applyPowerSave();   // hardware duty-cycle RX on/off from prefs
+  void applyApc();         // Adaptive Power Control on/off from prefs
   void applyFont();
   void applyRotation();
   void applyFullRefreshInterval();