[BattOr] Reduce StartTracing time by about four seconds.

tools/battor_agent/battor_agent.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 #include "tools/battor_agent/battor_agent.h"
 
 #include <iomanip>
 
 #include "base/bind.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "tools/battor_agent/battor_connection_impl.h"
@@ skipping 208 matching lines @@
       return;
     case Action::SEND_SAMPLES_REQUEST:
       PerformAction(Action::READ_CALIBRATION_FRAME);
       return;
     case Action::SEND_CURRENT_SAMPLE_REQUEST:
       PerformAction(Action::READ_CURRENT_SAMPLE);
       return;
     case Action::SEND_GIT_HASH_REQUEST:
       PerformAction(Action::READ_GIT_HASH);
       return;
+    case Action::RESET:
+      CompleteCommand(BATTOR_ERROR_NONE);
+      return;
     default:
       NOTREACHED();
       return;
   }
 }
 
 void BattOrAgent::OnMessageRead(bool success,
                                 BattOrMessageType type,
                                 std::unique_ptr<vector<char>> bytes) {
   if (!success) {
@@ skipping 106 matching lines @@
         RetryCommand();
         return;
       }
 
       // Check for the empty frame the BattOr uses to indicate it's done
       // streaming samples.
       if (frame.empty()) {
         // Cancel the next data frame timeout.
         timeout_callback_.Cancel();
         CompleteCommand(BATTOR_ERROR_NONE);
+
+        // Proactively reset the BattOr to speed up the next trace.
+        //
+        // Without this proactive reset, the BattOr will take several seconds
+        // to automatically reset the next time that a trace is started. By
+        // proactively resetting the BattOr now, before the trace is printed by
+        // the agent, the reset is parallelized with the final processing of
+        // this trace by the agent. Thus the BattOr will be ready to start
+        // the next trace immediately.
+        PerformAction(Action::RESET);
         return;
       }
 
       samples_.insert(samples_.end(), frame.begin(), frame.end());
 
       PerformAction(Action::READ_DATA_FRAME);
       return;
     }
 
     case Action::READ_CURRENT_SAMPLE:
@@ skipping 103 matching lines @@
 
     case Action::SEND_GIT_HASH_REQUEST:
       SendControlMessage(
           BATTOR_CONTROL_MESSAGE_TYPE_GET_FIRMWARE_GIT_HASH, 0, 0);
       return;
 
     case Action::READ_GIT_HASH:
       connection_->ReadMessage(BATTOR_MESSAGE_TYPE_CONTROL_ACK);
       return;
 
+    case Action::RESET:
+      SendControlMessage(BATTOR_CONTROL_MESSAGE_TYPE_RESET, 0, 0);
+      return;
+
     case Action::INVALID:
       NOTREACHED();
       return;
   }
 }
 
 void BattOrAgent::PerformDelayedAction(Action action, base::TimeDelta delay) {
   base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
       FROM_HERE, base::Bind(&BattOrAgent::PerformAction, AsWeakPtr(), action),
       delay);
@@ skipping 136 matching lines @@
 
 void BattOrAgent::SetActionTimeout(uint16_t timeout_seconds) {
   timeout_callback_.Reset(
       base::Bind(&BattOrAgent::OnActionTimeout, AsWeakPtr()));
   base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
       FROM_HERE, timeout_callback_.callback(),
       base::TimeDelta::FromSeconds(timeout_seconds));
 }
 
 }  // namespace battor