AP_GPS: fixed ublox M10S auto-config

this copes with the M10S rejecting multiple-key VALGET calls. We fall
back to fetching one at a time

libraries/AP_GPS/AP_GPS_UBLOX.cpp

@@ -994,6 +994,40 @@ AP_GPS_UBLOX::_parse_gps(void)
                 }
             }
         }
+        if(_msg_id == MSG_ACK_NACK) {
+            switch(_buffer.nack.clsID) {
+            case CLASS_CFG:
+                switch(_buffer.nack.msgID) {
+                case MSG_CFG_VALGET:
+                    if (active_config.list != nullptr) {
+                        /*
+                          likely this device does not support fetching multiple keys at once, go one at a time
+                        */
+                        if (active_config.fetch_index == -1) {
+                            Debug("NACK starting %u", unsigned(active_config.count));
+                            active_config.fetch_index = 0;
+                        } else {
+                            // the device does not support the config key we asked for,
+                            // consider the bit as done
+                            active_config.done_mask |= (1U<<active_config.fetch_index);
+                            Debug("NACK %d 0x%x done=0x%x",
+                                     int(active_config.fetch_index),
+                                     unsigned(active_config.list[active_config.fetch_index].key),
+                                     unsigned(active_config.done_mask));
+                            if (active_config.done_mask == (1U<<active_config.count)-1) {
+                                // all done!
+                                _unconfigured_messages &= ~active_config.unconfig_bit;
+                            }
+                            active_config.fetch_index++;
+                        }
+                        if (active_config.fetch_index < active_config.count) {
+                            _configure_valget(active_config.list[active_config.fetch_index].key);
+                        }
+                    }
+                    break;
+                }
+            }
+        }
         return false;
     }
 
@@ -1226,6 +1260,16 @@ AP_GPS_UBLOX::_parse_gps(void)
                             _unconfigured_messages &= ~active_config.unconfig_bit;
                         }
                     }
+                    if (active_config.fetch_index >= 0 &&
+                        active_config.fetch_index < active_config.count &&
+                        id == active_config.list[active_config.fetch_index].key) {
+                        active_config.fetch_index++;
+                        if (active_config.fetch_index < active_config.count) {
+                            _configure_valget(active_config.list[active_config.fetch_index].key);
+                            Debug("valget %d 0x%x", int(active_config.fetch_index),
+                                  unsigned(active_config.list[active_config.fetch_index].key));
+                        }
+                    }
                 }
 
                 // step over the value
@@ -1823,6 +1867,11 @@ AP_GPS_UBLOX::_configure_config_set(const config_list *list, uint8_t count, uint
     active_config.done_mask = 0;
     active_config.unconfig_bit = unconfig_bit;
     active_config.layers = layers;
+    // we start by fetching multiple values at once (with fetch_index
+    // -1) then if we get a NACK for VALGET we switch to fetching one
+    // value at a time. This copes with the M10S which can only fetch
+    // one value at a time
+    active_config.fetch_index = -1;
 
     uint8_t buf[sizeof(ubx_cfg_valget)+count*sizeof(ConfigKey)];
     struct ubx_cfg_valget msg {};

libraries/AP_GPS/AP_GPS_UBLOX.h

@@ -565,6 +565,10 @@ private:
         uint8_t clsID;
         uint8_t msgID;
     };
+    struct PACKED ubx_ack_nack {
+        uint8_t clsID;
+        uint8_t msgID;
+    };
 
 
     struct PACKED ubx_cfg_cfg {
@@ -618,6 +622,7 @@ private:
         ubx_rxm_rawx rxm_rawx;
 #endif
         ubx_ack_ack ack;
+        ubx_ack_nack nack;
         ubx_tim_tm2 tim_tm2;
     } _buffer;
 
@@ -849,6 +854,7 @@ private:
         uint32_t done_mask;
         uint32_t unconfig_bit;
         uint8_t layers;
+        int8_t fetch_index;
     } active_config;
 
 #if GPS_MOVING_BASELINE