Add FrSky BLE trainer (head tracker) support to the TX backpack

html/scan.js

@@ -7,6 +7,7 @@ function _(el) {
 function init() {
     initAat();
     initMavLink();
+    initBleTrainer();
 
     // sends XMLHttpRequest, so do it last
     initOptions();
@@ -47,6 +48,55 @@ function initMavLink() {
     xmlhttp.open('GET', '/mavlink', true);
     xmlhttp.send();
 }
+
+function initBleTrainer() {
+    const form = _('bt_form');
+    if (!form)
+        return;
+    form.addEventListener('submit', (e) => { e.preventDefault(); btSubmit(false); });
+    _('bt_forget').addEventListener('click', (e) => { e.preventDefault(); btSubmit(true); });
+    _('bt_source').addEventListener('change', () => btToggleBleSettings(_('bt_source').value));
+}
+
+// Posts the FrSky BLE Trainer form (or a Forget request) and updates the page
+// in place, so no manual reload is needed.
+function btSubmit(clearPeer) {
+    const body = clearPeer ? new URLSearchParams({ forget: 1 })
+                           : new URLSearchParams(new FormData(_('bt_form')));
+    const xmlhttp = new XMLHttpRequest();
+    xmlhttp.onreadystatechange = function () {
+        if (this.readyState != 4)
+            return;
+        if (this.status == 200) {
+            if (clearPeer) {
+                _('bt_status').textContent = 'Not paired';
+                _('bt_mac').textContent = '-';
+            }
+            cuteAlert({
+                type: 'success',
+                title: 'Bluetooth Trainer',
+                message: 'Bluetooth trainer settings saved'
+            });
+        } else {
+            cuteAlert({
+                type: 'error',
+                title: 'Bluetooth Trainer',
+                message: 'An error occurred saving the Bluetooth trainer settings'
+            });
+        }
+    };
+    xmlhttp.open('POST', '/settrainer', true);
+    xmlhttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
+    xmlhttp.send(body);
+}
+
+// Bluetooth-only fields are hidden when the native source is selected.
+function btToggleBleSettings(source) {
+    const el = _('bt_ble_settings');
+    if (el)
+        el.style.display = (source === 'native') ? 'none' : 'block';
+}
+
 function initOptions() {
     const xmlhttp = new XMLHttpRequest();
     xmlhttp.onreadystatechange = function() {
@@ -136,6 +186,15 @@ function updateConfig(data) {
     if (config['head-tracking']) {
         if (_('httab')) _('httab').style.display = 'table-cell';
     }
+    if (config['trainer']) {
+        if (_('bttab')) _('bttab').style.display = 'table-cell';
+        const bt = config.trainer;
+        _('bt_status').textContent = bt.paired ? 'Paired' : 'Not paired';
+        _('bt_mac').textContent = bt.paired ? bt.mac : '-';
+        _('bt_interval').value = bt.interval;
+        _('bt_source').value = bt.source;
+        btToggleBleSettings(bt.source);
+    }
     if((!data.stm32 || data.stm32==="no") && _('tx_tab')) {
         mui.tabs.activate('pane-justified-2');
         _('tx_tab').style.display = 'none';

html/txbp_index.html

@@ -26,6 +26,7 @@ <h1><b>ExpressLRS</b></h1>
 				<li><a data-mui-toggle="tab" data-mui-controls="pane-justified-2">Backpack</a></li>
 				<li><a data-mui-toggle="tab" data-mui-controls="pane-justified-3">Network</a></li>
 				<li><a data-mui-toggle="tab" data-mui-controls="pane-justified-4">MavLink</a></li>
+				<li id="bttab" style="display:none;"><a data-mui-toggle="tab" data-mui-controls="pane-bt">FrSky BLE Trainer</a></li>
 			</ul>
 
 			<div class="mui-tabs__pane mui--is-active" id="pane-justified-1">
@@ -146,6 +147,48 @@ <h3>MavLink Statistics</h3>
 					</tr>
 				</table>
 			</div>
+
+			<div class="mui-tabs__pane" id="pane-bt">
+				<h2>FrSky BLE Trainer</h2>
+				<p>The backpack forwards trainer channels to EdgeTX (as trainer input) from one of
+				two sources: the <b>native</b> system (ESP-NOW, e.g. a VRX or goggles with IMU) or a
+				<b>Bluetooth</b> device advertising the FrSky trainer service (e.g. an Arduino-based
+				HeadTracker). Both respect the radio's HT Enable; use the selector to choose which one
+				is used.</p>
+				<form id="bt_form" class="mui-form">
+					<div class="mui-select">
+						<select id="bt_source" name="source">
+							<option value="auto">Auto (Bluetooth if connected, else native)</option>
+							<option value="native">Native (ESP-NOW / VRX)</option>
+							<option value="ble">Bluetooth (BLE)</option>
+						</select>
+						<label>Trainer source</label>
+					</div>
+					<div id="bt_ble_settings">
+						<h3>Bluetooth device</h3>
+						<table class="mui-table">
+							<tr>
+								<td>Status:</td>
+								<td id="bt_status">-</td>
+							</tr>
+							<tr>
+								<td>Paired address:</td>
+								<td id="bt_mac">-</td>
+							</tr>
+						</table>
+						<div class="mui-textfield">
+							Connection interval (ms)
+							<input type="number" id="bt_interval" name="interval" min="7" max="1000">
+						</div>
+						<p>The trainer sends one frame per Bluetooth connection event, so a low
+						interval is what keeps the movement fluid. 8 ms suits a HeadTracker; higher
+						values only slow the stream down.</p>
+						<button type="button" id="bt_forget" class="mui-btn mui-btn--danger">Forget (re-pair on next boot)</button>
+						<br/><br/>
+					</div>
+					<input type="submit" value="Save" class="mui-btn mui-btn--primary">
+				</form>
+			</div>
 		</div>
 	</div>
 	<footer>

include/BleTrainer.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include "device.h"
+
+// Bluetooth trainer bridge: the backpack acts as a BLE central and connects to
+// a device that advertises the FrSky trainer service (0xFFF0/0xFFF6), such as a
+// HeadTracker, parses the FrSky trainer frame and emits
+// MSP_ELRS_BACKPACK_SET_PTR over Serial towards the ELRS module.
+//
+// Compiled only on BLE-capable targets (ESP32-C3/S3/ESP32) with HAS_BLE_TRAINER.
+
+#if defined(HAS_BLE_TRAINER)
+
+extern device_t BleTrainer_device;
+
+// True while a trainer is connected over BLE.
+bool bleTrainerConnected();
+
+// Forget the paired peer and go back to pairing mode (button long press).
+void bleTrainerForgetPeer();
+
+// Retained-RAM diagnostic: number of forwarded trainer packets, read from /config
+// (the Nomad backpack has no USB console).
+uint32_t bleTrainerSetPtrCount();
+
+#endif

lib/BUTTON/devButton.cpp

@@ -6,6 +6,7 @@
 #if defined(PIN_BUTTON)
 #include "logging.h"
 #include "button.h"
+#include "BleTrainer.h"
 
 static Button<PIN_BUTTON, false> button;
 
@@ -24,9 +25,21 @@ static void shortPress()
     }
 }
 
+#if defined(HAS_BLE_TRAINER)
+// Long press: forget the paired Bluetooth trainer so it can be re-paired.
+static void longPress()
+{
+    DBGLN("Button long: forget Bluetooth trainer peer");
+    bleTrainerForgetPeer();
+}
+#endif
+
 static void initialize()
 {
     button.OnShortPress = shortPress;
+#if defined(HAS_BLE_TRAINER)
+    button.OnLongPress = longPress;
+#endif
 }
 
 static int start()

lib/WIFI/devWIFI.cpp

@@ -52,6 +52,11 @@ extern wifi_service_t wifiService;
 #if defined(MAVLINK_ENABLED)
 extern MAVLink mavlink;
 #endif
+#if defined(HAS_BLE_TRAINER)
+#include <esp_attr.h>
+#include <esp_system.h>
+#include "BleTrainer.h"
+#endif
 #elif defined(TARGET_TIMER_BACKPACK)
 extern TimerBackpackConfig config;
 #else
@@ -103,6 +108,65 @@ extern bool headTrackingEnabled;
 #endif
 static bool servicesStarted = false;
 
+#if defined(TARGET_TX_BACKPACK)
+static void setMavlinkAccessPointSSID()
+{
+#if defined(PLATFORM_ESP32)
+  static const uint8_t unboundAddress[6] = {0, 0, 0, 0, 0, 0};
+  if (memcmp(firmwareOptions.uid, unboundAddress, sizeof(unboundAddress)) == 0)
+  {
+    const uint32_t suffix = (uint32_t)(ESP.getEfuseMac() & 0xFFFFFF);
+    snprintf(wifi_ap_ssid, sizeof(wifi_ap_ssid), "ExpressLRS TX Backpack %06lX",
+             (unsigned long)suffix);
+    return;
+  }
+#endif
+  snprintf(wifi_ap_ssid, sizeof(wifi_ap_ssid), "ExpressLRS TX Backpack %02X%02X%02X",
+           firmwareOptions.uid[3], firmwareOptions.uid[4], firmwareOptions.uid[5]);
+}
+#endif
+
+#if defined(HAS_BLE_TRAINER)
+// Boot forensics kept in retained RAM: the Nomad has no USB console, and the
+// MAVLink WiFi crash loop can only be diagnosed by reading, on the next boot,
+// what ended the previous one. Survives software/watchdog/brownout resets.
+#define TRAINER_BOOT_FX_MAGIC 0x48544246UL
+struct TrainerBootForensics
+{
+  uint32_t magic;
+  uint32_t boots;
+};
+RTC_NOINIT_ATTR static TrainerBootForensics s_bootFx;
+static uint32_t s_bootCount = 0;
+static int32_t s_thisReset = ESP_RST_UNKNOWN;
+
+static const char *resetReasonName(int32_t reason)
+{
+  switch (reason)
+  {
+    case ESP_RST_POWERON: return "power-on";
+    case ESP_RST_EXT: return "external-pin";
+    case ESP_RST_SW: return "software";
+    case ESP_RST_PANIC: return "panic";
+    case ESP_RST_INT_WDT: return "interrupt-watchdog";
+    case ESP_RST_TASK_WDT: return "task-watchdog";
+    case ESP_RST_WDT: return "other-watchdog";
+    case ESP_RST_DEEPSLEEP: return "deep-sleep";
+    case ESP_RST_BROWNOUT: return "brownout";
+    case ESP_RST_SDIO: return "sdio";
+    default: return "unknown";
+  }
+}
+
+static void captureBootForensics()
+{
+  s_thisReset = (int32_t)esp_reset_reason();
+  s_bootCount = (s_bootFx.magic == TRAINER_BOOT_FX_MAGIC) ? s_bootFx.boots + 1 : 1;
+  s_bootFx.magic = TRAINER_BOOT_FX_MAGIC;
+  s_bootFx.boots = s_bootCount;
+}
+#endif
+
 static bool target_seen = false;
 static uint8_t target_pos = 0;
 static String target_found;
@@ -314,6 +378,23 @@ static void GetConfiguration(AsyncWebServerRequest *request)
 #if defined(HAS_HEADTRACKING) || defined(SUPPORT_HEADTRACKING)
   json["config"]["head-tracking"] = true;
 #endif
+#if defined(HAS_BLE_TRAINER)
+  json["config"]["trainer"]["paired"] = config.IsTrainerPaired();
+  json["config"]["trainer"]["interval"] = config.GetTrainerIntervalMs();
+  const uint8_t *trainerMac = config.GetTrainerPeerMac();
+  char trainerMacStr[18];
+  snprintf(trainerMacStr, sizeof(trainerMacStr), "%02X:%02X:%02X:%02X:%02X:%02X",
+           trainerMac[0], trainerMac[1], trainerMac[2], trainerMac[3], trainerMac[4], trainerMac[5]);
+  json["config"]["trainer"]["mac"] = trainerMacStr;
+  const char *trainerSource = "auto";
+  if (config.GetTrainerSource() == TRAINER_SOURCE_ESPNOW) trainerSource = "native";
+  else if (config.GetTrainerSource() == TRAINER_SOURCE_BLE) trainerSource = "ble";
+  json["config"]["trainer"]["source"] = trainerSource;
+  json["config"]["trainer"]["boots"] = s_bootCount;
+  json["config"]["trainer"]["lastreset"] = resetReasonName(s_thisReset);
+  json["config"]["trainer"]["linked"] = bleTrainerConnected();
+  json["config"]["trainer"]["setptr"] = bleTrainerSetPtrCount();
+#endif
 #if defined(AAT_BACKPACK)
   WebAatAppendConfig(json);
 #endif
@@ -621,6 +702,34 @@ static void WebUpdateSetMavLink(AsyncWebServerRequest *request)
 }
 #endif
 
+#if defined(HAS_BLE_TRAINER)
+static void WebUpdateSetTrainer(AsyncWebServerRequest *request)
+{
+  if (request->hasArg("interval"))
+  {
+    int interval = request->arg("interval").toInt();
+    config.SetTrainerIntervalMs((uint16_t)constrain(interval, 7, 1000));
+  }
+  if (request->hasArg("source"))
+  {
+    String source = request->arg("source");
+    if (source == "native" || source == "espnow")
+      config.SetTrainerSource(TRAINER_SOURCE_ESPNOW);
+    else if (source == "ble")
+      config.SetTrainerSource(TRAINER_SOURCE_BLE);
+    else
+      config.SetTrainerSource(TRAINER_SOURCE_AUTO);
+  }
+  if (request->hasArg("forget") && request->arg("forget") != "0")
+  {
+    config.ClearTrainerPeerMac();
+  }
+  config.Commit();
+  DBGLN("Bluetooth trainer configuration updated");
+  request->send(200, "text/plain", "Bluetooth trainer settings saved");
+}
+#endif
+
 static void wifiOff()
 {
   wifiStarted = false;
@@ -748,6 +857,9 @@ static void startServices()
   #if defined(MAVLINK_ENABLED)
   server.on("/setmavlink", WebUpdateSetMavLink);
   #endif
+  #if defined(HAS_BLE_TRAINER)
+  server.on("/settrainer", HTTP_POST, WebUpdateSetTrainer);
+  #endif
   server.on("/forget", WebUpdateForget);
   server.on("/connect", WebUpdateConnect);
   server.on("/access", WebUpdateAccessPoint);
@@ -800,6 +912,15 @@ static void startServices()
 static void HandleWebUpdate()
 {
   unsigned long now = millis();
+#if defined(HAS_BLE_TRAINER)
+  static unsigned long lastStatusLog = 0;
+  if (now - lastStatusLog > 3000)
+  {
+    lastStatusLog = now;
+    DBGLN("WIFI status mode=%d started=%d services=%d ap=%s", (int)wifiMode, wifiStarted,
+          servicesStarted, WiFi.softAPIP().toString().c_str());
+  }
+#endif
   wl_status_t status = WiFi.status();
   if (status != laststatus && wifiMode == WIFI_STA) {
     DBGLN("WiFi status %d", status);
@@ -843,12 +964,7 @@ static void HandleWebUpdate()
         }
         else if (wifiService == WIFI_SERVICE_MAVLINK_TX)
         {
-          // Generate a unique SSID using config.address as hex
-          sprintf(wifi_ap_ssid, "ExpressLRS TX Backpack %02X%02X%02X",
-            firmwareOptions.uid[3],
-            firmwareOptions.uid[4],
-            firmwareOptions.uid[5]
-          );
+          setMavlinkAccessPointSSID();
         }
 #endif
         WiFi.softAP(wifi_ap_ssid, wifi_ap_password);
@@ -945,11 +1061,10 @@ static void HandleWebUpdate()
     #endif
     // When in STA mode, a small delay reduces power use from 90mA to 30mA when idle
     // In AP mode, it doesn't seem to make a measurable difference, but does not hurt
-#if defined(MAVLINK_ENABLED)
-    if (!updater.isRunning() && wifiService != WIFI_SERVICE_MAVLINK_TX)
-#else
+    // The ESP32-C3 is single-core: always yield to the idle task here. Skipping
+    // the delay in MAVLINK_TX lets this tight poll loop starve the idle task
+    // once BLE adds its radio tasks, which resets the whole chip.
     if (!updater.isRunning())
-#endif
       delay(1);
     if (do_flash) {
       do_flash = false;
@@ -995,6 +1110,9 @@ static void HandleWebUpdate()
 
 static int start()
 {
+#if defined(HAS_BLE_TRAINER)
+  captureBootForensics();
+#endif
   return DURATION_NEVER;
 }