Convert aos over to flatbuffers

Everything builds, and all the tests pass.  I suspect that some entries
are missing from the config files, but those will be found pretty
quickly on startup.

There is no logging or live introspection of queue messages.

Change-Id: I496ee01ed68f202c7851bed7e8786cee30df29f5
diff --git a/aos/events/ping.cc b/aos/events/ping.cc
new file mode 100644
index 0000000..b904cb2
--- /dev/null
+++ b/aos/events/ping.cc
@@ -0,0 +1,88 @@
+#include <chrono>
+
+#include "aos/configuration.h"
+#include "aos/events/pingpong_generated.h"
+#include "aos/events/shm_event_loop.h"
+#include "aos/init.h"
+#include "aos/json_to_flatbuffer.h"
+#include "gflags/gflags.h"
+#include "glog/logging.h"
+
+DEFINE_int32(sleep_ms, 10, "Time to sleep between pings");
+
+namespace aos {
+
+namespace chrono = std::chrono;
+
+class Ping {
+ public:
+  Ping(EventLoop *event_loop)
+      : event_loop_(event_loop),
+        sender_(event_loop_->MakeSender<examples::Ping>("/test")) {
+    timer_handle_ = event_loop_->AddTimer([this]() { SendPing(); });
+
+    event_loop_->MakeWatcher(
+        "/test", [this](const examples::Pong &pong) { HandlePong(pong); });
+
+    event_loop_->OnRun([this]() {
+      timer_handle_->Setup(event_loop_->monotonic_now(),
+                           chrono::milliseconds(FLAGS_sleep_ms));
+    });
+
+    event_loop_->SetRuntimeRealtimePriority(5);
+  }
+
+  void SendPing() {
+    ++count_;
+    aos::Sender<examples::Ping>::Builder msg = sender_.MakeBuilder();
+    examples::Ping::Builder builder = msg.MakeBuilder<examples::Ping>();
+    builder.add_value(count_);
+    builder.add_send_time(
+        event_loop_->monotonic_now().time_since_epoch().count());
+    CHECK(msg.Send(builder.Finish()));
+    VLOG(2) << "Sending ping";
+  }
+
+  void HandlePong(const examples::Pong &pong) {
+    const aos::monotonic_clock::time_point monotonic_send_time(
+        chrono::nanoseconds(pong.initial_send_time()));
+    const aos::monotonic_clock::time_point monotonic_now =
+        event_loop_->monotonic_now();
+
+    const chrono::nanoseconds round_trip_time =
+        monotonic_now - monotonic_send_time;
+
+    if (pong.value() == count_) {
+      VLOG(1) << "Elapsed time " << round_trip_time.count() << " ns "
+              << FlatbufferToJson(&pong);
+    } else {
+      VLOG(1) << "Missmatched pong message";
+    }
+  }
+
+ private:
+  EventLoop *event_loop_;
+  aos::Sender<examples::Ping> sender_;
+  TimerHandler *timer_handle_;
+  int count_ = 0;
+};
+
+}  // namespace aos
+
+int main(int argc, char **argv) {
+  FLAGS_logtostderr = true;
+  google::InitGoogleLogging(argv[0]);
+  ::gflags::ParseCommandLineFlags(&argc, &argv, true);
+
+  aos::FlatbufferDetachedBuffer<aos::Configuration> config =
+      aos::configuration::ReadConfig("aos/events/config.fb.json");
+
+  ::aos::ShmEventLoop event_loop(&config.message());
+
+  aos::Ping ping(&event_loop);
+
+  event_loop.Run();
+
+  ::aos::Cleanup();
+  return 0;
+}