fix(nrf52): run app loop on dedicated FreeRTOS task to avoid stack overflow

examples/simple_repeater/main.cpp

@@ -3,6 +3,11 @@
 
 #include "MyMesh.h"
 
+#if defined(NRF52_PLATFORM)
+#include <helpers/MeshWorkerTask.h>
+static void meshAppLoop();   // forward decl: setup() passes it to startMeshWorker()
+#endif
+
 #ifdef DISPLAY_CLASS
   #include "UITask.h"
   static UITask ui_task(display);
@@ -105,9 +110,16 @@ void setup() {
 #endif
 
   board.onBootComplete();
+
+#if defined(NRF52_PLATFORM)
+  if (!startMeshWorker(meshAppLoop)) {
+    MESH_DEBUG_PRINTLN("Failed to start mesh worker task!");
+    halt();
+  }
+#endif
 }
 
-void loop() {
+static void meshAppLoop() {
   board.loop();
 
   int len = strlen(command);
@@ -172,3 +184,11 @@ void loop() {
     #endif
   }
 }
+
+void loop() {
+#if defined(NRF52_PLATFORM)
+  vTaskDelay(pdMS_TO_TICKS(1000));   // app loop runs on the dedicated mesh worker task
+#else
+  meshAppLoop();
+#endif
+}

examples/simple_room_server/main.cpp

@@ -3,6 +3,11 @@
 
 #include "MyMesh.h"
 
+#if defined(NRF52_PLATFORM)
+#include <helpers/MeshWorkerTask.h>
+static void meshAppLoop();   // forward decl: setup() passes it to startMeshWorker()
+#endif
+
 #ifdef DISPLAY_CLASS
   #include "UITask.h"
   static UITask ui_task(display);
@@ -82,9 +87,16 @@ void setup() {
 #endif
 
   board.onBootComplete();
+
+#if defined(NRF52_PLATFORM)
+  if (!startMeshWorker(meshAppLoop)) {
+    MESH_DEBUG_PRINTLN("Failed to start mesh worker task!");
+    halt();
+  }
+#endif
 }
 
-void loop() {
+static void meshAppLoop() {
   board.loop();
 
   int len = strlen(command);
@@ -118,3 +130,11 @@ void loop() {
 #endif
   rtc_clock.tick();
 }
+
+void loop() {
+#if defined(NRF52_PLATFORM)
+  vTaskDelay(pdMS_TO_TICKS(1000));   // app loop runs on the dedicated mesh worker task
+#else
+  meshAppLoop();
+#endif
+}

src/helpers/MeshWorkerTask.cpp

@@ -0,0 +1,38 @@
+#include "MeshWorkerTask.h"
+
+#if defined(NRF52_PLATFORM)
+#include <Arduino.h>
+#include <MeshCore.h>   // MESH_DEBUG_PRINTLN
+#include <FreeRTOS.h>
+#include <task.h>
+
+static TaskHandle_t   _meshTaskHandle = nullptr;
+static void (*_meshLoopBody)() = nullptr;
+
+static void mesh_worker_task(void*) {
+  for (;;) {
+    if (_meshLoopBody) _meshLoopBody();
+    vTaskDelay(1);   // yield at least one tick (tick-rate independent)
+  }
+}
+
+bool startMeshWorker(void (*loopBody)()) {
+  if (loopBody == nullptr) {
+    MESH_DEBUG_PRINTLN("startMeshWorker: null loopBody");
+    return false;
+  }
+  if (_meshTaskHandle != nullptr) {
+    MESH_DEBUG_PRINTLN("startMeshWorker: already started");
+    return false;
+  }
+  _meshLoopBody = loopBody;
+  // 2048 words = 8KB stack (measured peak ~4.7KB + headroom).
+  // TASK_PRIO_LOW (1) matches the framework's own loop_task priority.
+  if (xTaskCreate(mesh_worker_task, "mesh", 2048, NULL, TASK_PRIO_LOW, &_meshTaskHandle) != pdPASS) {
+    MESH_DEBUG_PRINTLN("startMeshWorker: xTaskCreate failed (out of FreeRTOS heap?)");
+    _meshTaskHandle = nullptr;
+    return false;
+  }
+  return true;
+}
+#endif

src/helpers/MeshWorkerTask.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#if defined(NRF52_PLATFORM)
+// Run an application loop body on a dedicated FreeRTOS task with an 8KB stack,
+// instead of the Adafruit_nRF52_Arduino framework's Arduino loop_task (whose 4KB
+// stack -- LOOP_STACK_SZ = 256*4, an unconditional #define that build flags can't
+// override -- is too small for LittleFS file opens done from loop(), e.g.
+// ClientACL::saveSessionKeys, which overflow it and corrupt adjacent heap).
+//
+// Definitions live in MeshWorkerTask.cpp so there is a single shared instance.
+// Returns true if the task was created, false on FreeRTOS heap exhaustion.
+bool startMeshWorker(void (*loopBody)());
+#endif