Support sleep for NRF52 boards by suspending the main task

This uses the core functions suspendLoop() and resumeLoop() to suspend
the main task and put the CPU in a low power idle mode.

The wakeup occurs either through the specified timeout using a timer
interrupt or through an RX interrupt from the radio module.

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;
 };
 
 /*