GCS_MAVLink: send `AVAILABLE_MODES_MONITOR` message

libraries/GCS_MAVLink/GCS.h

@@ -1139,6 +1139,7 @@ private:
         uint8_t next_index;
     } available_modes;
     bool send_available_modes();
+    bool send_available_mode_monitor();
 
 };
 
@@ -1301,6 +1302,11 @@ public:
     MAV_RESULT lua_command_int_packet(const mavlink_command_int_t &packet);
 #endif
 
+    // Sequence number should be incremented when available modes changes
+    // Sent in AVAILABLE_MODES_MONITOR msg
+    uint8_t get_available_modes_sequence() const { return available_modes_sequence; }
+    void available_modes_changed() { available_modes_sequence += 1; }
+
 protected:
 
     virtual GCS_MAVLINK *new_gcs_mavlink_backend(GCS_MAVLINK_Parameters &params,
@@ -1378,6 +1384,10 @@ private:
     // GCS::update_send is called so we don't starve later links of
     // time in which they are permitted to send messages.
     uint8_t first_backend_to_send;
+
+    // Sequence number should be incremented when available modes changes
+    // Sent in AVAILABLE_MODES_MONITOR msg
+    uint8_t available_modes_sequence;
 };
 
 GCS &gcs();

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -1153,6 +1153,7 @@ ap_message GCS_MAVLINK::mavlink_id_to_ap_message_id(const uint32_t mavlink_id) c
         { MAVLINK_MSG_ID_AIRSPEED, MSG_AIRSPEED},
 #endif
         { MAVLINK_MSG_ID_AVAILABLE_MODES, MSG_AVAILABLE_MODES},
+        { MAVLINK_MSG_ID_AVAILABLE_MODES_MONITOR, MSG_AVAILABLE_MODES_MONITOR},
             };
 
     for (uint8_t i=0; i<ARRAY_SIZE(map); i++) {
@@ -3210,6 +3211,10 @@ MAV_RESULT GCS_MAVLINK::handle_command_request_message(const mavlink_command_int
         available_modes.should_send = true;
         available_modes.next_index = 1;
         available_modes.requested_index = (uint8_t)packet.param2;
+
+        // After the first request sequnece is streamed in the AVAILABLE_MODES_MONITOR message
+        // This allows the GCS to re-request modes if there is a change
+        set_ap_message_interval(MSG_AVAILABLE_MODES_MONITOR, 5000);
         break;
 
     default:
@@ -6137,6 +6142,18 @@ bool GCS_MAVLINK::send_available_modes()
     return true;
 }
 
+bool GCS_MAVLINK::send_available_mode_monitor()
+{
+    CHECK_PAYLOAD_SIZE(AVAILABLE_MODES_MONITOR);
+
+    mavlink_msg_available_modes_monitor_send(
+        chan,
+        gcs().get_available_modes_sequence()
+    );
+
+    return true;
+}
+
 bool GCS_MAVLINK::try_send_message(const enum ap_message id)
 {
     bool ret = true;
@@ -6571,6 +6588,10 @@ bool GCS_MAVLINK::try_send_message(const enum ap_message id)
         ret = send_available_modes();
         break;
 
+    case MSG_AVAILABLE_MODES_MONITOR:
+        ret = send_available_mode_monitor();
+        break;
+
     default:
         // try_send_message must always at some stage return true for
         // a message, or we will attempt to infinitely retry the

libraries/GCS_MAVLink/ap_message.h

@@ -104,5 +104,6 @@ enum ap_message : uint8_t {
 #endif
     MSG_AIRSPEED,
     MSG_AVAILABLE_MODES,
+    MSG_AVAILABLE_MODES_MONITOR,
     MSG_LAST // MSG_LAST must be the last entry in this enum
 };