APM: much faster parameter fetching

allow up to 30% of bandwidth to be used for parameter send

ArduPlane/GCS.h

@@ -153,6 +153,7 @@ private:
     uint16_t                    _queued_parameter_count; ///< saved count of
                                                          // parameters for
                                                          // queued send
+    uint32_t                    _queued_parameter_send_time_ms;
 
     /// Count the number of reportable parameters.
     ///

ArduPlane/GCS_Mavlink.pde

@@ -1989,31 +1989,47 @@ GCS_MAVLINK::_count_parameters()
 void
 GCS_MAVLINK::queued_param_send()
 {
-    // Check to see if we are sending parameters
+    if (_queued_parameter == NULL) {
-    if (NULL == _queued_parameter) return;
+        return;
+    }
+
+    uint16_t bytes_allowed;
+    uint8_t count;
+    uint32_t tnow = millis();
 
-    AP_Param      *vp;
+    // use at most 30% of bandwidth on parameters. The constant 26 is
-    float value;
+    // 1/(1000 * 1/8 * 0.001 * 0.3)
+    bytes_allowed = g.serial3_baud * (tnow - _queued_parameter_send_time_ms) * 26;
+    if (bytes_allowed > comm_get_txspace(chan)) {
+        bytes_allowed = comm_get_txspace(chan);
+    }
+    count = bytes_allowed / (MAVLINK_MSG_ID_PARAM_VALUE_LEN + MAVLINK_NUM_NON_PAYLOAD_BYTES);
 
-    // copy the current parameter and prepare to move to the next
+    while (_queued_parameter != NULL && count--) {
-    vp = _queued_parameter;
+        AP_Param      *vp;
+        float value;
 
-    // if the parameter can be cast to float, report it here and break out of the loop
+        // copy the current parameter and prepare to move to the next
-    value = vp->cast_to_float(_queued_parameter_type);
+        vp = _queued_parameter;
 
-    char param_name[ONBOARD_PARAM_NAME_LENGTH];
+        // if the parameter can be cast to float, report it here and break out of the loop
-    vp->copy_name(param_name, sizeof(param_name), true);
+        value = vp->cast_to_float(_queued_parameter_type);
 
-    mavlink_msg_param_value_send(
+        char param_name[ONBOARD_PARAM_NAME_LENGTH];
-        chan,
+        vp->copy_name(param_name, sizeof(param_name), true);
-        param_name,
+
-        value,
+        mavlink_msg_param_value_send(
-        mav_var_type(_queued_parameter_type),
+            chan,
-        _queued_parameter_count,
+            param_name,
-        _queued_parameter_index);
+            value,
-
+            mav_var_type(_queued_parameter_type),
-    _queued_parameter = AP_Param::next_scalar(&_queued_parameter_token, &_queued_parameter_type);
+            _queued_parameter_count,
-    _queued_parameter_index++;
+            _queued_parameter_index);
+
+        _queued_parameter = AP_Param::next_scalar(&_queued_parameter_token, &_queued_parameter_type);
+        _queued_parameter_index++;
+    }
+    _queued_parameter_send_time_ms = tnow;
 }
 
 /**