ArduPilotPlugin: add option to disable SITL from trying to sync with wall time

- Populate extra fields in JSON message.
- Generally Gazebo runs with simulation time, so we do not want to sync with the wall clock.
- When running SITL on a docker container using a windows or macOS host, the monotonic clock can jump to a different epoch if there is a vDSO page fault. This results in a FPE and crash.

Signed-off-by: Rhys Mainwaring <rhys.mainwaring@me.com>

Author: srmainwaring

include/ArduPilotPlugin.hh

@@ -84,6 +84,9 @@ class ArduPilotPluginPrivate;
 /// <anemometer>  scoped name for the wind sensor
 /// <connectionTimeoutMaxCount> timeout before giving up on
 ///                             controller synchronization
+/// <lock_step>           set true to enforce lock-step simulation
+/// <no_time_sync>        set true to prevent SITL from trying to sync
+///                       with wall-time
 /// <have_32_channels>    set true if 32 channels are enabled
 ///
 class GZ_SIM_VISIBLE ArduPilotPlugin:

src/ArduPilotPlugin.cc

@@ -244,6 +244,9 @@ class gz::sim::systems::ArduPilotPluginPrivate
   /// \brief Set true to enforce lock-step simulation
   public: bool isLockStep{false};
 
+  /// \brief Set true to prevent SITL from trying to sync with wall-time
+  public: bool isNoTimeSync{true};
+
   /// \brief Set true if have 32 servo channels
   public: bool have32Channels{false};
 
@@ -510,7 +513,11 @@ void gz::sim::systems::ArduPilotPlugin::Configure(
   this->dataPtr->isLockStep =
     sdfClone->Get("lock_step", this->dataPtr->isLockStep).first;
 
-  this->dataPtr->have32Channels =
+  // Prevent SITL attempting time-sync (has default: true)
+  this->dataPtr->isNoTimeSync =
+    sdfClone->Get("no_time_sync", this->dataPtr->isNoTimeSync).first;
+
+    this->dataPtr->have32Channels =
     sdfClone->Get("have_32_channels", false).first;
 
   // Add the signal handler
@@ -2000,6 +2007,14 @@ void gz::sim::systems::ArduPilotPlugin::CreateStateJSON(
       writer.EndObject();
     }
 
+    // Set no time sync
+    writer.Key("no_time_sync");
+    writer.Bool(this->dataPtr->isNoTimeSync);
+
+    // Set no lockstep
+    writer.Key("no_lockstep");
+    writer.Bool(!this->dataPtr->isLockStep);
+
     writer.EndObject();
 
     // get JSON