From 1e0a2fb0bef69c8d68b0ec9f005095622d7b6db9 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <tridge@samba.org>
Date: Fri, 30 Mar 2012 17:22:48 +1100
Subject: [PATCH] MAVLink: don't waste 100 bytes of bandwidth sending 1 byte of
 information

the GPS_STATUS message is a massive waste of bandwidth, but it is the
only message that tells us the number of visible satellites. So only
send it if that information changes.

This makes MAVLink work better at low baud rates
---
 ArduCopter/GCS.h           |  4 ++++
 ArduCopter/GCS_Mavlink.pde | 11 +++++++++--
 ArduPlane/GCS.h            |  4 ++++
 ArduPlane/GCS_Mavlink.pde  | 10 +++++++++-
 4 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/ArduCopter/GCS.h b/ArduCopter/GCS.h
index 7047beaf09..6a1fc4182c 100644
--- a/ArduCopter/GCS.h
+++ b/ArduCopter/GCS.h
@@ -43,6 +43,7 @@ public:
 	void		init(FastSerial *port) {
         _port = port;
         initialised = true;
+        last_gps_satellites = 255;
     }
 
 	/// Update GCS state.
@@ -89,6 +90,9 @@ public:
     // set to true if this GCS link is active
     bool initialised;
 
+    // used to prevent wasting bandwidth with GPS_STATUS messages
+    uint8_t last_gps_satellites;
+
 protected:
 	/// The stream we are communicating over
 	FastSerial			*_port;
diff --git a/ArduCopter/GCS_Mavlink.pde b/ArduCopter/GCS_Mavlink.pde
index 8cb0957367..bdd0f217cd 100644
--- a/ArduCopter/GCS_Mavlink.pde
+++ b/ArduCopter/GCS_Mavlink.pde
@@ -697,11 +697,18 @@ GCS_MAVLINK::data_stream_send(uint16_t freqMin, uint16_t freqMax)
 		if (freqLoopMatch(streamRateExtendedStatus, freqMin, freqMax)) {
 			send_message(MSG_EXTENDED_STATUS1);
 			send_message(MSG_EXTENDED_STATUS2);
-			send_message(MSG_GPS_STATUS);
 			send_message(MSG_CURRENT_WAYPOINT);
 			send_message(MSG_GPS_RAW);			// TODO - remove this message after location message is working
 			send_message(MSG_NAV_CONTROLLER_OUTPUT);
-			//Serial.printf("mav2 %d\n", (int)streamRateExtendedStatus.get());
+
+            if (last_gps_satellites != g_gps->num_sats) {
+                // this message is mostly a huge waste of bandwidth,
+                // except it is the only message that gives the number
+                // of visible satellites. So only send it when that
+                // changes.
+                send_message(MSG_GPS_STATUS);
+                last_gps_satellites = g_gps->num_sats;
+            }
 		}
 
 		if (freqLoopMatch(streamRatePosition, freqMin, freqMax)) {
diff --git a/ArduPlane/GCS.h b/ArduPlane/GCS.h
index 7047beaf09..6a1fc4182c 100644
--- a/ArduPlane/GCS.h
+++ b/ArduPlane/GCS.h
@@ -43,6 +43,7 @@ public:
 	void		init(FastSerial *port) {
         _port = port;
         initialised = true;
+        last_gps_satellites = 255;
     }
 
 	/// Update GCS state.
@@ -89,6 +90,9 @@ public:
     // set to true if this GCS link is active
     bool initialised;
 
+    // used to prevent wasting bandwidth with GPS_STATUS messages
+    uint8_t last_gps_satellites;
+
 protected:
 	/// The stream we are communicating over
 	FastSerial			*_port;
diff --git a/ArduPlane/GCS_Mavlink.pde b/ArduPlane/GCS_Mavlink.pde
index 2cede18da0..3d7e2d35b3 100644
--- a/ArduPlane/GCS_Mavlink.pde
+++ b/ArduPlane/GCS_Mavlink.pde
@@ -900,11 +900,19 @@ GCS_MAVLINK::data_stream_send(uint16_t freqMin, uint16_t freqMax)
 		if (freqLoopMatch(streamRateExtendedStatus, freqMin, freqMax)) {
 			send_message(MSG_EXTENDED_STATUS1);
 			send_message(MSG_EXTENDED_STATUS2);
-			send_message(MSG_GPS_STATUS);
 			send_message(MSG_CURRENT_WAYPOINT);
 			send_message(MSG_GPS_RAW);            // TODO - remove this message after location message is working
 			send_message(MSG_NAV_CONTROLLER_OUTPUT);
 			send_message(MSG_FENCE_STATUS);
+
+            if (last_gps_satellites != g_gps->num_sats) {
+                // this message is mostly a huge waste of bandwidth,
+                // except it is the only message that gives the number
+                // of visible satellites. So only send it when that
+                // changes.
+                send_message(MSG_GPS_STATUS);
+                last_gps_satellites = g_gps->num_sats;
+            }
 		}
 
 		if (freqLoopMatch(streamRatePosition, freqMin, freqMax)) {