add new (not yet used) interface for downlink transport using function pointers

sw/airborne/downlink_transport.h

@@ -0,0 +1,50 @@
+/*
+ * Paparazzi $Id: downlink_transport.h 4766 2010-03-30 10:00:29Z hecto $
+ *  
+ * Copyright (C) 2003-2006  Pascal Brisset, Antoine Drouin
+ *
+ * This file is part of paparazzi.
+ *
+ * paparazzi is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * paparazzi is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with paparazzi; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA. 
+ *
+ */
+
+/** \file downlink_transport.h
+ *  \brief Interface for downlink transport implementation
+ *
+ */
+
+#ifndef DOWNLINK_TRANSPORT_H
+#define DOWNLINK_TRANSPORT_H
+
+#include <inttypes.h>
+
+struct DownlinkTransport
+{
+	uint8_t (*SizeOf)(void *impl, uint8_t size);
+	int (*CheckFreeSpace)(void *impl, uint8_t size);
+
+	void (*PutBytes)(void *impl, uint8_t len, const uint8_t *bytes);
+
+	void (*StartMessage)(void *impl, char *name, uint8_t msg_id, uint8_t payload_len);
+	void (*EndMessage)(void *impl);
+	void (*Overrun)(void *impl);
+	void (*CountBytes)(void *impl, uint8_t len);
+
+	void *impl;
+};
+
+#endif /* DOWNLINK_TRANSPORT_H */