Add TinyGsmAutoBaud

TinyGsmCommon.h

@@ -71,4 +71,26 @@ const T& TinyGsmMax(const T& a, const T& b)
     return (b < a) ? a : b;
 }
 
+template<class T>
+uint32_t TinyGsmAutoBaud(T& SerialAT)
+{
+  static uint32_t rates[] = { 115200, 57600, 38400, 19200, 9600, 74400, 74880, 230400, 460800, 2400, 4800, 14400, 28800 };
+
+  for (unsigned i = 0; i < sizeof(rates)/sizeof(rates[0]); i++) {
+    uint32_t rate = rates[i];
+    DBG("Trying baud rate", rate, "...");
+    SerialAT.begin(rate);
+    delay(10);
+    for (int i=0; i<3; i++) {
+      SerialAT.print("AT\r\n");
+      String input = SerialAT.readString();
+      if (input.indexOf("OK") >= 0) {
+        DBG("Modem responded at rate", rate);
+        return rate;
+      }
+    }
+  }
+  return 0;
+}
+
 #endif