GCS_MAVLink: added have_flow_control() method

can be used to change speed of handling some protocol methods, as we
know communication will be reliable

libraries/GCS_MAVLink/GCS.h

@@ -287,10 +287,14 @@ private:
     void handle_mission_request_list(AP_Mission &mission, mavlink_message_t *msg);
     void handle_mission_request(AP_Mission &mission, mavlink_message_t *msg, 
                                 AP_Mission::Mission_Command &cmd);
+
     void handle_mission_set_current(AP_Mission &mission, mavlink_message_t *msg);
     void handle_mission_count(AP_Mission &mission, mavlink_message_t *msg);
     void handle_mission_clear_all(AP_Mission &mission, mavlink_message_t *msg);
     void handle_mission_write_partial_list(AP_Mission &mission, mavlink_message_t *msg);
+
+    // return true if this channel has hardware flow control
+    bool have_flow_control(void);
 };
 
 #endif // __GCS_H

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -365,3 +365,22 @@ void GCS_MAVLINK::handle_mission_write_partial_list(AP_Mission &mission, mavlink
     waypoint_request_i   = packet.start_index;
     waypoint_request_last= packet.end_index;
 }
+
+/*
+  return true if a channel has flow control
+ */
+bool GCS_MAVLINK::have_flow_control(void)
+{
+    switch (chan) {
+    case MAVLINK_COMM_0:
+        // assume USB has flow control
+        return hal.gpio->usb_connected() || hal.uartA->get_flow_control() != AP_HAL::UARTDriver::FLOW_CONTROL_DISABLE;
+
+    case MAVLINK_COMM_1:
+        return hal.uartC->get_flow_control() != AP_HAL::UARTDriver::FLOW_CONTROL_DISABLE;
+
+    case MAVLINK_COMM_2:
+        return hal.uartD != NULL && hal.uartD->get_flow_control() != AP_HAL::UARTDriver::FLOW_CONTROL_DISABLE;
+    }
+    return false;
+}

libraries/GCS_MAVLink/GCS_Logs.cpp

@@ -141,12 +141,7 @@ void GCS_MAVLINK::handle_log_send(DataFlash_Class &dataflash)
     if (chan == MAVLINK_COMM_0 && hal.gpio->usb_connected()) {
         // when on USB we can send a lot more data
         num_sends = 40;
-    } else if (chan == MAVLINK_COMM_1 && 
-               hal.uartC->get_flow_control() != AP_HAL::UARTDriver::FLOW_CONTROL_DISABLE) {
-        num_sends = 10;        
-    } else if (chan == MAVLINK_COMM_2 && 
-               hal.uartD != NULL &&
-               hal.uartD->get_flow_control() != AP_HAL::UARTDriver::FLOW_CONTROL_DISABLE) {
+    } else if (have_flow_control()) {
         num_sends = 10;        
     }