Move PDP measurement fetching to a separate thread

Stupid CAN messages are too slow for being inline with the normal
path...

Change-Id: I160a24eb3216fc54083df576555b5bcad062ceb8
diff --git a/frc971/wpilib/BUILD b/frc971/wpilib/BUILD
index c07b7f8..7a7d7bb 100644
--- a/frc971/wpilib/BUILD
+++ b/frc971/wpilib/BUILD
@@ -170,5 +170,22 @@
     '//aos/common/messages:robot_state',
     '//aos/externals:wpilib',
     '//aos/common/logging:queue_logging',
+    ':pdp_fetcher',
+  ],
+)
+
+cc_library(
+  name = 'pdp_fetcher',
+  srcs = [
+    'pdp_fetcher.cc',
+  ],
+  hdrs = [
+    'pdp_fetcher.h',
+  ],
+  deps = [
+    '//aos/common/messages:robot_state',
+    '//aos/externals:wpilib',
+    '//aos/common/logging:queue_logging',
+    '//aos/linux_code:init',
   ],
 )
diff --git a/frc971/wpilib/loop_output_handler.h b/frc971/wpilib/loop_output_handler.h
index d7b6283..972d7ef 100644
--- a/frc971/wpilib/loop_output_handler.h
+++ b/frc971/wpilib/loop_output_handler.h
@@ -1,12 +1,12 @@
 #ifndef FRC971_WPILIB_LOOP_OUTPUT_HANDLER_H_
 #define FRC971_WPILIB_LOOP_OUTPUT_HANDLER_H_
 
+#include <atomic>
+
 #include "aos/common/scoped_fd.h"
 #include "aos/common/time.h"
 #include "aos/common/util/log_interval.h"
 
-#include <atomic>
-
 namespace frc971 {
 namespace wpilib {
 
diff --git a/frc971/wpilib/pdp_fetcher.cc b/frc971/wpilib/pdp_fetcher.cc
new file mode 100644
index 0000000..1c87107
--- /dev/null
+++ b/frc971/wpilib/pdp_fetcher.cc
@@ -0,0 +1,52 @@
+#include "frc971/wpilib/pdp_fetcher.h"
+
+#include "aos/common/logging/queue_logging.h"
+#include "aos/linux_code/init.h"
+
+namespace frc971 {
+namespace wpilib {
+
+PDPFetcher::PDPFetcher() : pdp_(new PowerDistributionPanel()) {
+  pdp_values_.Zero();
+}
+
+void PDPFetcher::GetValues(::aos::PDPValues *pdp_values) {
+  ::aos::MutexLocker locker(&values_lock_);
+  *pdp_values = pdp_values_;
+}
+
+void PDPFetcher::operator()() {
+  ::aos::SetCurrentThreadName("PDPFetcher");
+  // Something in WPILib blocks for long periods of time in here, so it's not
+  // actually a busy loop like it looks. It seems to somehow be related to
+  // joystick packets.
+  while (true) {
+    {
+      const double voltage = pdp_->GetVoltage();
+      ::aos::MutexLocker locker(&values_lock_);
+      pdp_values_.voltage = voltage;
+    }
+    {
+      const double temperature = pdp_->GetTemperature();
+      ::aos::MutexLocker locker(&values_lock_);
+      pdp_values_.temperature = temperature;
+    }
+    {
+      const double power = pdp_->GetTotalPower();
+      ::aos::MutexLocker locker(&values_lock_);
+      pdp_values_.power = power;
+    }
+    for (int i = 0; i < 16; ++i) {
+      const double current = pdp_->GetCurrent(i);
+      ::aos::MutexLocker locker(&values_lock_);
+      pdp_values_.currents[i] = current;
+    }
+    {
+      ::aos::MutexLocker locker(&values_lock_);
+      LOG_STRUCT(DEBUG, "finished fetching", pdp_values_);
+    }
+  }
+}
+
+}  // namespace wpilib
+}  // namespace frc971
diff --git a/frc971/wpilib/pdp_fetcher.h b/frc971/wpilib/pdp_fetcher.h
new file mode 100644
index 0000000..8271f2b
--- /dev/null
+++ b/frc971/wpilib/pdp_fetcher.h
@@ -0,0 +1,42 @@
+#ifndef FRC971_WPILIB_PDP_FETCHER_H_
+#define FRC971_WPILIB_PDP_FETCHER_H_
+
+#include <memory>
+#include <atomic>
+
+#include "aos/common/messages/robot_state.q.h"
+#include "aos/common/mutex.h"
+
+#include "PowerDistributionPanel.h"
+
+namespace frc971 {
+namespace wpilib {
+
+// Handles fetching values from the PDP. This is slow, so it has to happen in a
+// separate thread.
+class PDPFetcher {
+ public:
+  PDPFetcher();
+
+  void Quit() { run_ = false; }
+
+  // Retrieves the latest set of values and stores it in *pdp_values.
+  // This is safe to call from any thread.
+  void GetValues(::aos::PDPValues *pdp_values);
+
+  // To be called by a ::std::thread.
+  void operator()();
+
+ private:
+  const ::std::unique_ptr<PowerDistributionPanel> pdp_;
+
+  ::aos::PDPValues pdp_values_;
+  ::aos::Mutex values_lock_;
+
+  ::std::atomic<bool> run_{true};
+};
+
+}  // namespace wpilib
+}  // namespace frc971
+
+#endif  // FRC971_WPILIB_PDP_FETCHER_H_
diff --git a/frc971/wpilib/wpilib_interface.cc b/frc971/wpilib/wpilib_interface.cc
index 2129ec3..5df3c9c 100644
--- a/frc971/wpilib/wpilib_interface.cc
+++ b/frc971/wpilib/wpilib_interface.cc
@@ -3,6 +3,8 @@
 #include "aos/common/messages/robot_state.q.h"
 #include "aos/common/logging/queue_logging.h"
 
+#include "frc971/wpilib/pdp_fetcher.h"
+
 #include "DriverStation.h"
 #include "ControllerPower.h"
 #undef ERROR
@@ -11,7 +13,7 @@
 namespace wpilib {
 
 void SendRobotState(int32_t my_pid, DriverStation *ds,
-                    PowerDistributionPanel *pdp) {
+                    PDPFetcher *pdp_fetcher) {
   auto new_state = ::aos::robot_state.MakeMessage();
 
   new_state->reader_pid = my_pid;
@@ -26,12 +28,7 @@
   new_state->voltage_roborio_in = ControllerPower::GetInputVoltage();
   new_state->voltage_battery = ds->GetBatteryVoltage();
 
-  new_state->pdp_voltage = pdp->GetVoltage();
-  new_state->pdp_temperature = pdp->GetTemperature();
-  new_state->pdp_power = pdp->GetTotalPower();
-  for (int i = 0; i < 16; ++i) {
-    new_state->pdp_currents[i] = pdp->GetCurrent(i);
-  }
+  pdp_fetcher->GetValues(&new_state->pdp);
 
   LOG_STRUCT(DEBUG, "robot_state", *new_state);
 
diff --git a/frc971/wpilib/wpilib_interface.h b/frc971/wpilib/wpilib_interface.h
index 7d4b92d..82936ec 100644
--- a/frc971/wpilib/wpilib_interface.h
+++ b/frc971/wpilib/wpilib_interface.h
@@ -3,16 +3,16 @@
 
 #include <stdint.h>
 
-#include "PowerDistributionPanel.h"
-
 class DriverStation;
 
 namespace frc971 {
 namespace wpilib {
 
+class PDPFetcher;
+
 // Sends out a message on ::aos::robot_state.
 void SendRobotState(int32_t my_pid, DriverStation *ds,
-                    PowerDistributionPanel *pdp);
+                    PDPFetcher *pdp_fetcher);
 
 }  // namespace wpilib
 }  // namespace frc971