allow to start m5 atom s3 without USB device connected

lib/serial/GwSerial.h

@@ -16,17 +16,19 @@ class GwSerial : public GwChannelInterface{
         int id=-1;
         int overflows=0;
         size_t enqueue(const uint8_t *data, size_t len,bool partial=false);
-        HardwareSerial *serial;
+        Stream *serial;
+        bool availableWrite=false; //if this is false we will wait for availabkleWrite until we flush again
     public:
         static const int bufferSize=200;
-        GwSerial(GwLog *logger,HardwareSerial *stream,int id,bool allowRead=true);
+        GwSerial(GwLog *logger,Stream *stream,int id,bool allowRead=true);
         ~GwSerial();
         bool isInitialized();
         virtual size_t sendToClients(const char *buf,int sourceId,bool partial=false);
         virtual void loop(bool handleRead=true,bool handleWrite=true);
         virtual void readMessages(GwMessageFetcher *writer);
-        void flush();
+        bool flush(long millis=200);
         virtual Stream *getStream(bool partialWrites);
+        bool getAvailableWrite(){return availableWrite;}
     friend GwSerialStream;
 };
 #endif