Feature: SDM power meter: switch to software serial

a 9600 baud serial interface does not need a hardware UART. these
changes switch the SDM power meter implementation to use a software
serial instance instead. this is desirable as hardware UARTs are scarce
and users need them for JK BMS and VE.Direct interfaces.

include/PowerMeterSerialSdm.h

@@ -4,6 +4,7 @@
 #include <atomic>
 #include <mutex>
 #include <condition_variable>
+#include <SoftwareSerial.h>
 #include "Configuration.h"
 #include "PowerMeterProvider.h"
 #include "SDM.h"
@@ -49,8 +50,7 @@ class PowerMeterSerialSdm : public PowerMeterProvider {
 
     mutable std::mutex _valueMutex;
 
-    static char constexpr _sdmSerialPortOwner[] = "SDM power meter";
-    std::unique_ptr<HardwareSerial> _upSdmSerial = nullptr;
+    std::unique_ptr<SoftwareSerial> _upSdmSerial = nullptr;
     std::unique_ptr<SDM> _upSdm = nullptr;
 
     TaskHandle_t _taskHandle = nullptr;

lib/SdmEnergyMeter/SDM.cpp

@@ -393,8 +393,18 @@ void SDM::modbusWrite(uint8_t* data, size_t messageLength) {
     resptime = millis() + waitForBytesSent_ms;
   }
 
+#if !defined ( USE_HARDWARESERIAL )
+  // prevent scheduler from messing up the serial message. this task shall only
+  // be scheduled after the whole serial message was transmitted.
+  vTaskSuspendAll();
+#endif
+
   sdmSer.write(data, messageLength);                                            //send 8 bytes
-
+
+#if !defined ( USE_HARDWARESERIAL )
+  xTaskResumeAll();
+#endif
+
   if (_dere_pin != NOT_A_PIN) {
     const int32_t timeleft = (int32_t) (resptime - millis());
     if (timeleft > 0) {

lib/SdmEnergyMeter/SDM_Config_User.h

@@ -14,7 +14,7 @@
 *  define or undefine USE_HARDWARESERIAL (uncomment only one or none)
 */
 //#undef USE_HARDWARESERIAL
-#define USE_HARDWARESERIAL
+//#define USE_HARDWARESERIAL
 
 //------------------------------------------------------------------------------
 

src/PowerMeterSerialSdm.cpp

@@ -23,8 +23,6 @@ PowerMeterSerialSdm::~PowerMeterSerialSdm()
         _upSdmSerial->end();
         _upSdmSerial = nullptr;
     }
-
-    SerialPortManager.freePort(_sdmSerialPortOwner);
 }
 
 bool PowerMeterSerialSdm::init()
@@ -40,13 +38,9 @@ bool PowerMeterSerialSdm::init()
         return false;
     }
 
-    auto oHwSerialPort = SerialPortManager.allocatePort(_sdmSerialPortOwner);
-    if (!oHwSerialPort) { return false; }
-
-    _upSdmSerial = std::make_unique<HardwareSerial>(*oHwSerialPort);
-    _upSdmSerial->end(); // make sure the UART will be re-initialized
+    _upSdmSerial = std::make_unique<SoftwareSerial>();
     _upSdm = std::make_unique<SDM>(*_upSdmSerial, 9600, pin.powermeter_dere,
-            SERIAL_8N1, pin.powermeter_rx, pin.powermeter_tx);
+            SWSERIAL_8N1, pin.powermeter_rx, pin.powermeter_tx);
     _upSdm->begin();
 
     std::unique_lock<std::mutex> lock(_pollingMutex);