Feature: SDM power meter: poll asynchronously

include/PowerMeterSerialSdm.h

@@ -1,7 +1,9 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 #pragma once
 
+#include <atomic>
 #include <mutex>
+#include <condition_variable>
 #include "Configuration.h"
 #include "PowerMeterProvider.h"
 #include "SDM.h"
@@ -20,16 +22,20 @@ public:
     ~PowerMeterSerialSdm();
 
     bool init() final;
-    void loop() final;
+    void loop() final { } // polling is performed asynchronously
     float getPowerTotal() const final;
     bool isDataValid() const final;
     void doMqttPublish() const final;
 
 private:
+    static void pollingLoopHelper(void* context);
+    std::atomic<bool> _taskDone;
+    void pollingLoop();
+
     Phases _phases;
     PowerMeterSerialSdmConfig const _cfg;
 
-    uint32_t _lastPoll;
+    uint32_t _lastPoll = 0;
 
     float _phase1Power = 0.0;
     float _phase2Power = 0.0;
@@ -40,9 +46,14 @@ private:
     float _energyImport = 0.0;
     float _energyExport = 0.0;
 
-    mutable std::mutex _mutex;
+    mutable std::mutex _valueMutex;
 
     static char constexpr _sdmSerialPortOwner[] = "SDM power meter";
     std::unique_ptr<HardwareSerial> _upSdmSerial = nullptr;
     std::unique_ptr<SDM> _upSdm = nullptr;
+
+    TaskHandle_t _taskHandle = nullptr;
+    bool _stopPolling;
+    mutable std::mutex _pollingMutex;
+    std::condition_variable _cv;
 };

src/PowerMeterSerialSdm.cpp

@@ -6,6 +6,19 @@
 
 PowerMeterSerialSdm::~PowerMeterSerialSdm()
 {
+    _taskDone = false;
+
+    std::unique_lock<std::mutex> lock(_pollingMutex);
+    _stopPolling = true;
+    lock.unlock();
+
+    _cv.notify_all();
+
+    if (_taskHandle != nullptr) {
+        while (!_taskDone) { delay(10); }
+        _taskHandle = nullptr;
+    }
+
     if (_upSdmSerial) {
         _upSdmSerial->end();
         _upSdmSerial = nullptr;
@@ -34,12 +47,20 @@ bool PowerMeterSerialSdm::init()
             SERIAL_8N1, pin.powermeter_rx, pin.powermeter_tx);
     _upSdm->begin();
 
+    std::unique_lock<std::mutex> lock(_pollingMutex);
+    _stopPolling = false;
+    lock.unlock();
+
+    uint32_t constexpr stackSize = 3072;
+    xTaskCreate(PowerMeterSerialSdm::pollingLoopHelper, "PM:SDM",
+            stackSize, this, 1/*prio*/, &_taskHandle);
+
     return true;
 }
 
 float PowerMeterSerialSdm::getPowerTotal() const
 {
-    std::lock_guard<std::mutex> l(_mutex);
+    std::lock_guard<std::mutex> l(_valueMutex);
     return _phase1Power + _phase2Power + _phase3Power;
 }
 
@@ -51,7 +72,7 @@ bool PowerMeterSerialSdm::isDataValid() const
 
 void PowerMeterSerialSdm::doMqttPublish() const
 {
-    std::lock_guard<std::mutex> l(_mutex);
+    std::lock_guard<std::mutex> l(_valueMutex);
     mqttPublish("power1", _phase1Power);
     mqttPublish("power2", _phase2Power);
     mqttPublish("power3", _phase3Power);
@@ -62,14 +83,30 @@ void PowerMeterSerialSdm::doMqttPublish() const
     mqttPublish("export", _energyExport);
 }
 
-void PowerMeterSerialSdm::loop()
+void PowerMeterSerialSdm::pollingLoopHelper(void* context)
 {
-    if (!_upSdm) { return; }
+    auto pInstance = static_cast<PowerMeterSerialSdm*>(context);
+    pInstance->pollingLoop();
+    pInstance->_taskDone = true;
+    vTaskDelete(nullptr);
+}
 
-    if ((millis() - _lastPoll) < (_cfg.PollingInterval * 1000)) {
-        return;
+void PowerMeterSerialSdm::pollingLoop()
+{
+    std::unique_lock<std::mutex> lock(_pollingMutex);
+
+    while (!_stopPolling) {
+        auto elapsedMillis = millis() - _lastPoll;
+        auto intervalMillis = _cfg.PollingInterval * 1000;
+        if (_lastPoll > 0 && elapsedMillis < intervalMillis) {
+            auto sleepMs = intervalMillis - elapsedMillis;
+            _cv.wait_for(lock, std::chrono::milliseconds(sleepMs),
+                    [this] { return _stopPolling; }); // releases the mutex
+            continue;
         }
 
+        _lastPoll = millis();
+
         uint8_t addr = _cfg.Address;
 
         // reading takes a "very long" time as each readVal() is a synchronous
@@ -92,7 +129,7 @@ void PowerMeterSerialSdm::loop()
         }
 
         {
-        std::lock_guard<std::mutex> l(_mutex);
+            std::lock_guard<std::mutex> l(_valueMutex);
             _phase1Power = static_cast<float>(phase1Power);
             _phase2Power = static_cast<float>(phase2Power);
             _phase3Power = static_cast<float>(phase3Power);
@@ -103,9 +140,8 @@ void PowerMeterSerialSdm::loop()
             _energyExport = static_cast<float>(energyExport);
         }
 
-    gotUpdate();
-
         MessageOutput.printf("[PowerMeterSerialSdm] TotalPower: %5.2f\r\n", getPowerTotal());
 
-    _lastPoll = millis();
+        gotUpdate();
+    }
 }