Support sleep for NRF52 boards by suspending the main task

This uses FreeRTOS direct task notifications as recommended in the
docs.

Using the Arduino core functions suspendLoop() and resumeLoop() can
lead to deadlocks which can only be avoided by disabling IRQs and
possibly missing incoming packets.

Signed-off-by: Frieder Schrempf <frieder@fris.de>

Author: fschrempf

src/helpers/NRF52Board.cpp

@@ -5,6 +5,8 @@
 
 static BLEDfu bledfu;
 
+BaseType_t wakeup_event;
+
 static void connect_callback(uint16_t conn_handle) {
   (void)conn_handle;
   MESH_DEBUG_PRINTLN("BLE client connected");
@@ -19,6 +21,18 @@ static void disconnect_callback(uint16_t conn_handle, uint8_t reason) {
 
 void NRF52Board::begin() {
   startup_reason = BD_STARTUP_NORMAL;
+  loop_task_handle = xTaskGetHandle("loop");
+}
+
+void NRF52Board::sleep(uint32_t secs) {
+  MESH_DEBUG_PRINTLN("Suspending loop for powersaving, set wakeup timer in %u seconds", secs);
+  ulTaskNotifyTake(pdFALSE, pdMS_TO_TICKS(secs * 1000));
+}
+
+void NRF52Board::onRXInterrupt() {
+  BaseType_t higher_priority_task_woken = pdFALSE;
+  vTaskNotifyGiveFromISR(loop_task_handle, &higher_priority_task_woken);
+  portYIELD_FROM_ISR(higher_priority_task_woken);
 }
 
 void NRF52BoardDCDC::begin() {

src/helpers/NRF52Board.h

@@ -6,6 +6,9 @@
 #if defined(NRF52_PLATFORM)
 
 class NRF52Board : public mesh::MainBoard {
+private:
+  TaskHandle_t loop_task_handle;
+
 protected:
   uint8_t startup_reason;
 
@@ -14,6 +17,8 @@ class NRF52Board : public mesh::MainBoard {
   virtual uint8_t getStartupReason() const override { return startup_reason; }
   virtual float getMCUTemperature() override;
   virtual void reboot() override { NVIC_SystemReset(); }
+  virtual void sleep(uint32_t secs) override;
+  virtual void onRXInterrupt() override;
 };
 
 /*