Sub: allow GCS MAVLink base class to handle out-of-time for sending messages

ArduSub/GCS_Mavlink.cpp

@@ -219,14 +219,6 @@ bool GCS_Sub::vehicle_initialised() const {
 // try to send a message, return false if it won't fit in the serial tx buffer
 bool GCS_MAVLINK_Sub::try_send_message(enum ap_message id)
 {
-    // if we don't have at least 250 micros remaining before the main loop
-    // wants to fire then don't send a mavlink message. We want to
-    // prioritise the main flight control loop over communications
-    if (sub.scheduler.time_available_usec() < 250 && sub.motors.armed()) {
-        gcs().set_out_of_time(true);
-        return false;
-    }
-
     switch (id) {
 
     case MSG_NAMED_FLOAT:

ArduSub/GCS_Sub.h

@@ -27,6 +27,16 @@ public:
 
     bool vehicle_initialised() const override;
 
+protected:
+
+    // minimum amount of time (in microseconds) that must remain in
+    // the main scheduler loop before we are allowed to send any
+    // mavlink messages.  We want to prioritise the main flight
+    // control loop over communications
+    uint16_t min_loop_time_remaining_for_message_send_us() const override {
+        return 250;
+    }
+
 private:
 
     GCS_MAVLINK_Sub _chan[MAVLINK_COMM_NUM_BUFFERS];