Add minimum frame length on the morse decoder

examples/test_morse_decoder.grc

@@ -1,5 +1,5 @@
 <?xml version='1.0' encoding='utf-8'?>
-<?grc format='1' created='3.7.10'?>
+<?grc format='1' created='3.7.11'?>
 <flow_graph>
   <timestamp>Fri Jan 22 20:01:21 2016</timestamp>
   <block>
@@ -131,6 +131,14 @@
       <key>debug_seq</key>
       <value>"SATNOGS HELLO EARTH WORLD 123456789"</value>
     </param>
+    <param>
+      <key>seq_pause_ms</key>
+      <value>1000</value>
+    </param>
+    <param>
+      <key>wpm</key>
+      <value>20</value>
+    </param>
   </block>
   <block>
     <key>satnogs_morse_decoder</key>
@@ -170,6 +178,10 @@
       <key>minoutbuf</key>
       <value>0</value>
     </param>
+    <param>
+      <key>min_frame_len</key>
+      <value>3</value>
+    </param>
     <param>
       <key>unrecognized_char</key>
       <value>ord('#')</value>

grc/satnogs_morse_decoder.xml

@@ -3,7 +3,7 @@
 	<name>Morse Decoder</name>
 	<key>satnogs_morse_decoder</key>
 	<import>import satnogs</import>
-	<make>satnogs.morse_decoder($unrecognized_char)</make>
+	<make>satnogs.morse_decoder($unrecognized_char, $min_frame_len)</make>
 
 	<param>
 		<name>Unrecognized character</name>
@@ -11,6 +11,13 @@
 		<value>ord('#')</value>
 		<type>int</type>
 	</param>
+	
+	<param>
+		<name>Minimum frame length</name>
+		<key>min_frame_len</key>
+		<value>3</value>
+		<type>int</type>
+	</param>
 
 
 	<sink>

include/satnogs/morse_decoder.h

@@ -42,8 +42,10 @@ namespace gr {
        * @param unrecognized_char the character that will be placed
        * in situations where the decoder can not decide which character
        * was received.
+       * @param min_frame_len the minimum frame length in order to reduce
+       * false alarms
        */
-      static sptr make(char unrecognized_char = '#');
+      static sptr make(char unrecognized_char = '#', size_t min_frame_len = 3);
     };
 
   } // namespace satnogs

lib/morse_decoder_impl.cc

@@ -32,10 +32,10 @@ namespace gr
   {
 
     morse_decoder::sptr
-    morse_decoder::make (char unrecognized_char)
+    morse_decoder::make (char unrecognized_char, size_t min_frame_len)
     {
       return gnuradio::get_initial_sptr (
-          new morse_decoder_impl (unrecognized_char));
+          new morse_decoder_impl (unrecognized_char, min_frame_len));
     }
 
     void
@@ -69,9 +69,11 @@ namespace gr
             break;
           }
           str = d_morse_tree.get_word ();
-          d_morse_tree.reset ();
+          if (str.length () > d_min_frame_len) {
-          message_port_pub (pmt::mp ("out"),
+            d_morse_tree.reset ();
-                            pmt::make_blob (str.c_str (), str.length ()));
+            message_port_pub (pmt::mp ("out"),
+                              pmt::make_blob (str.c_str (), str.length ()));
+          }
           break;
         case MORSE_INTRA_SPACE:
           /*Ignore it */
@@ -98,10 +100,13 @@ namespace gr
     /*
      * The private constructor
      */
-    morse_decoder_impl::morse_decoder_impl (char unrecognized_char) :
+    morse_decoder_impl::morse_decoder_impl (char unrecognized_char,
+                                            size_t min_frame_len) :
             gr::block ("morse_decoder", gr::io_signature::make (0, 0, 0),
                        gr::io_signature::make (0, 0, 0)),
-            d_morse_tree (unrecognized_char)
+            d_morse_tree (unrecognized_char),
+            d_min_frame_len (min_frame_len)
+
     {
       /* Register the input and output msg handler */
       message_port_register_in (pmt::mp ("in"));

lib/morse_decoder_impl.h

@@ -31,12 +31,13 @@ namespace gr {
     {
      private:
       morse_tree d_morse_tree;
+      size_t d_min_frame_len;
 
       void
       symbol_msg_handler(pmt::pmt_t msg);
 
      public:
-      morse_decoder_impl(char unrecognized_char);
+      morse_decoder_impl(char unrecognized_char, size_t min_frame_len);
 
     };