Merge tag 'spark_4' into compile-server2

Tag version 0.2.1 as spark_4

Author: David Middlecamp

src/spark_protocol.cpp

@@ -793,6 +793,8 @@ bool SparkProtocol::handle_received_message(void)
       int return_value = descriptor.call_function(function_key, function_arg);
 
       // send return value
+      *msg_to_send = 0;
+      *(msg_to_send + 1) = 16;
       function_return(msg_to_send + 2, token, return_value);
       if (0 > blocking_send(msg_to_send, 18))
       {
@@ -874,9 +876,16 @@ bool SparkProtocol::handle_received_message(void)
       unsigned int given_crc = queue[8] << 24 | queue[9] << 16 | queue[10] << 8 | queue[11];
       if (callback_calculate_crc(queue + 13, len - 13 - queue[len - 1]) == given_crc)
       {
-        callback_save_firmware_chunk(queue + 13, len - 13 - queue[len - 1]);
-        chunk_received(msg_to_send + 2, token, ChunkReceivedCode::OK);
-        ++chunk_index;
+    	unsigned short next_chunk_index = callback_save_firmware_chunk(queue + 13, len - 13 - queue[len - 1]);
+        if (next_chunk_index > chunk_index)
+        {
+          chunk_received(msg_to_send + 2, token, ChunkReceivedCode::OK);
+        }
+        else
+        {
+          chunk_missed(msg_to_send + 2, next_chunk_index);
+        }
+        chunk_index = next_chunk_index;
       }
       else
       {

src/spark_protocol.h

@@ -64,7 +64,7 @@ struct SparkCallbacks
   void (*prepare_for_firmware_update)(void);
   void (*finish_firmware_update)(void);
   long unsigned int (*calculate_crc)(unsigned char *buf, long unsigned int buflen);
-  void (*save_firmware_chunk)(unsigned char *buf, long unsigned int buflen);
+  unsigned short (*save_firmware_chunk)(unsigned char *buf, long unsigned int buflen);
   void (*signal)(bool on);
   system_tick_t (*millis)();
 };
@@ -142,7 +142,7 @@ class SparkProtocol
     void (*callback_prepare_for_firmware_update)(void);
     void (*callback_finish_firmware_update)(void);
     long unsigned int (*callback_calculate_crc)(unsigned char *buf, long unsigned int buflen);
-    void (*callback_save_firmware_chunk)(unsigned char *buf, long unsigned int buflen);
+    unsigned short (*callback_save_firmware_chunk)(unsigned char *buf, long unsigned int buflen);
     void (*callback_signal)(bool on);
     system_tick_t (*callback_millis)();