farm mode ping

Firmware/Marlin_main.cpp

@@ -231,7 +231,7 @@ CardReader card;
 
 unsigned long TimeSent = millis();
 unsigned long TimeNow = millis();
-
+unsigned long PingTime = millis();
 union Data
 {
 byte b[2];
@@ -1954,7 +1954,13 @@ void process_commands()
   int8_t SilentMode;
 #endif
   if(code_seen("PRUSA")){
-		if (code_seen("PRN")) {
+		if (code_seen("Ping")) {
+			if (farm_mode) {
+				PingTime = millis();
+				MYSERIAL.print(farm_no); MYSERIAL.println(" : OK");
+			}	  
+		}
+		else if (code_seen("PRN")) {
 		  MYSERIAL.println(status_number);
 
 		}else if (code_seen("fn")) {

Firmware/ultralcd.cpp

@@ -4473,6 +4473,9 @@ void lcd_update(uint8_t lcdDrawUpdateOverride)
 	  lcd_next_update_millis = millis() + LCD_UPDATE_INTERVAL;
 	  }
 	if (!SdFatUtil::test_stack_integrity()) stack_error();
+	if (farm_mode && ((millis() - PingTime) > PING_TIME * 1000)) {
+		// beep once per minute
+	}
 }
 
 void lcd_ignore_click(bool b)