Merge branch '2022'

CMakeLists.txt

@@ -187,6 +187,7 @@ if (WITH_GUI)
     add_subdirectory(imgui)
     add_subdirectory(wpigui)
     add_subdirectory(glass)
+    add_subdirectory(outlineviewer)
 endif()
 
 if (WITH_CSCORE)

cameraserver/multiCameraServer/src/main/java/edu/wpi/Main.java

@@ -10,8 +10,8 @@ import com.google.gson.JsonArray;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
 import com.google.gson.JsonParser;
-import edu.wpi.cscore.VideoSource;
 import edu.wpi.first.cameraserver.CameraServer;
+import edu.wpi.first.cscore.VideoSource;
 import edu.wpi.first.networktables.NetworkTableInstance;
 import java.io.IOException;
 import java.nio.file.Files;

cameraserver/multiCameraServer/src/main/native/cpp/main.cpp

@@ -158,7 +158,7 @@ bool ReadConfig() {
 void StartCamera(const CameraConfig& config) {
   wpi::outs() << "Starting camera '" << config.name << "' on " << config.path
               << '\n';
-  auto camera = frc::CameraServer::GetInstance()->StartAutomaticCapture(
+  auto camera = frc::CameraServer::GetInstance().StartAutomaticCapture(
       config.name, config.path);
 
   camera.SetConfigJson(config.config);

cameraserver/src/main/java/edu/wpi/first/cameraserver/CameraServer.java

@@ -4,20 +4,20 @@
 
 package edu.wpi.first.cameraserver;
 
-import edu.wpi.cscore.AxisCamera;
-import edu.wpi.cscore.CameraServerJNI;
-import edu.wpi.cscore.CvSink;
-import edu.wpi.cscore.CvSource;
-import edu.wpi.cscore.MjpegServer;
-import edu.wpi.cscore.UsbCamera;
-import edu.wpi.cscore.VideoEvent;
-import edu.wpi.cscore.VideoException;
-import edu.wpi.cscore.VideoListener;
-import edu.wpi.cscore.VideoMode;
-import edu.wpi.cscore.VideoMode.PixelFormat;
-import edu.wpi.cscore.VideoProperty;
-import edu.wpi.cscore.VideoSink;
-import edu.wpi.cscore.VideoSource;
+import edu.wpi.first.cscore.AxisCamera;
+import edu.wpi.first.cscore.CameraServerJNI;
+import edu.wpi.first.cscore.CvSink;
+import edu.wpi.first.cscore.CvSource;
+import edu.wpi.first.cscore.MjpegServer;
+import edu.wpi.first.cscore.UsbCamera;
+import edu.wpi.first.cscore.VideoEvent;
+import edu.wpi.first.cscore.VideoException;
+import edu.wpi.first.cscore.VideoListener;
+import edu.wpi.first.cscore.VideoMode;
+import edu.wpi.first.cscore.VideoMode.PixelFormat;
+import edu.wpi.first.cscore.VideoProperty;
+import edu.wpi.first.cscore.VideoSink;
+import edu.wpi.first.cscore.VideoSource;
 import edu.wpi.first.networktables.EntryListenerFlags;
 import edu.wpi.first.networktables.NetworkTable;
 import edu.wpi.first.networktables.NetworkTableEntry;

cameraserver/src/main/java/edu/wpi/first/vision/VisionRunner.java

@@ -4,9 +4,9 @@
 
 package edu.wpi.first.vision;
 
-import edu.wpi.cscore.CvSink;
-import edu.wpi.cscore.VideoSource;
 import edu.wpi.first.cameraserver.CameraServerSharedStore;
+import edu.wpi.first.cscore.CvSink;
+import edu.wpi.first.cscore.VideoSource;
 import org.opencv.core.Mat;
 
 /**

cameraserver/src/main/java/edu/wpi/first/vision/VisionThread.java

@@ -4,7 +4,7 @@
 
 package edu.wpi.first.vision;
 
-import edu.wpi.cscore.VideoSource;
+import edu.wpi.first.cscore.VideoSource;
 
 /**
  * A vision thread is a special thread that runs a vision pipeline. It is a <i>daemon</i> thread; it

cameraserver/src/main/java/edu/wpi/first/vision/package-info.java

@@ -13,7 +13,7 @@
  *     implements VisionRunner.Listener<MyFindTotePipeline> {
  *
  *      // A USB camera connected to the roboRIO.
- *      private {@link edu.wpi.cscore.VideoSource VideoSource} usbCamera;
+ *      private {@link edu.wpi.first.cscore.VideoSource VideoSource} usbCamera;
  *
  *      // A vision pipeline. This could be handwritten or generated by GRIP.
  *      // This has to implement {@link edu.wpi.first.vision.VisionPipeline}.

cameraserver/src/main/native/cpp/cameraserver/CameraServer.cpp

@@ -45,7 +45,7 @@ struct CameraServer::Impl {
   std::vector<std::string> m_addresses;
 };
 
-CameraServer* CameraServer::GetInstance() {
+CameraServer& CameraServer::GetInstance() {
   struct Creator {
     static void* call() { return new CameraServer{}; }
   };
@@ -53,7 +53,7 @@ CameraServer* CameraServer::GetInstance() {
     static void call(void* ptr) { delete static_cast<CameraServer*>(ptr); }
   };
   static wpi::ManagedStatic<CameraServer, Creator, Deleter> instance;
-  return &(*instance);
+  return *instance;
 }
 
 static wpi::StringRef MakeSourceValue(CS_Source source,

cameraserver/src/main/native/include/cameraserver/CameraServer.h

@@ -32,7 +32,7 @@ class CameraServer {
   /**
    * Get the CameraServer instance.
    */
-  static CameraServer* GetInstance();
+  static CameraServer& GetInstance();
 
   /**
    * Start automatically capturing images to send to the dashboard.

cscore/src/dev/java/edu/wpi/first/cscore/DevMain.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 import edu.wpi.first.wpiutil.RuntimeDetector;
 

cscore/src/main/java/edu/wpi/first/cscore/AxisCamera.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 /** A source that represents an Axis IP camera. */
 public class AxisCamera extends HttpCamera {

cscore/src/main/java/edu/wpi/first/cscore/CameraServerCvJNI.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 import edu.wpi.first.wpiutil.RuntimeLoader;
 import java.io.IOException;

cscore/src/main/java/edu/wpi/first/cscore/CameraServerJNI.java

@@ -2,9 +2,9 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
-import edu.wpi.cscore.raw.RawFrame;
+import edu.wpi.first.cscore.raw.RawFrame;
 import edu.wpi.first.wpiutil.RuntimeLoader;
 import java.io.IOException;
 import java.nio.ByteBuffer;

cscore/src/main/java/edu/wpi/first/cscore/CvSink.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 import org.opencv.core.Mat;
 

cscore/src/main/java/edu/wpi/first/cscore/CvSource.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 import org.opencv.core.Mat;
 

cscore/src/main/java/edu/wpi/first/cscore/HttpCamera.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 /** A source that represents a MJPEG-over-HTTP (IP) camera. */
 public class HttpCamera extends VideoCamera {

cscore/src/main/java/edu/wpi/first/cscore/ImageSink.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 public abstract class ImageSink extends VideoSink {
   protected ImageSink(int handle) {

cscore/src/main/java/edu/wpi/first/cscore/ImageSource.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 public abstract class ImageSource extends VideoSource {
   protected ImageSource(int handle) {

cscore/src/main/java/edu/wpi/first/cscore/MjpegServer.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 /** A sink that acts as a MJPEG-over-HTTP network server. */
 public class MjpegServer extends VideoSink {

cscore/src/main/java/edu/wpi/first/cscore/UsbCamera.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 /** A source that represents a USB camera. */
 public class UsbCamera extends VideoCamera {

cscore/src/main/java/edu/wpi/first/cscore/UsbCameraInfo.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 /** USB camera information. */
 public class UsbCameraInfo {

cscore/src/main/java/edu/wpi/first/cscore/VideoCamera.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 /** A source that represents a video camera. */
 public class VideoCamera extends VideoSource {

cscore/src/main/java/edu/wpi/first/cscore/VideoEvent.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 /** Video event. */
 public class VideoEvent {

cscore/src/main/java/edu/wpi/first/cscore/VideoException.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 /** An exception raised by the camera server. */
 public class VideoException extends RuntimeException {

cscore/src/main/java/edu/wpi/first/cscore/VideoListener.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 import java.util.HashMap;
 import java.util.Map;

cscore/src/main/java/edu/wpi/first/cscore/VideoMode.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 /** Video mode. */
 public class VideoMode {

cscore/src/main/java/edu/wpi/first/cscore/VideoProperty.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 /** A source or sink property. */
 public class VideoProperty {

cscore/src/main/java/edu/wpi/first/cscore/VideoSink.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 /**
  * A source for video that provides a sequence of frames. Each frame may consist of multiple images

cscore/src/main/java/edu/wpi/first/cscore/VideoSource.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 /**
  * A source for video that provides a sequence of frames. Each frame may consist of multiple images

cscore/src/main/java/edu/wpi/first/cscore/raw/RawFrame.java

@@ -2,9 +2,9 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore.raw;
+package edu.wpi.first.cscore.raw;
 
-import edu.wpi.cscore.CameraServerJNI;
+import edu.wpi.first.cscore.CameraServerJNI;
 import java.nio.ByteBuffer;
 
 /**

cscore/src/main/java/edu/wpi/first/cscore/raw/RawSink.java

@@ -2,10 +2,10 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore.raw;
+package edu.wpi.first.cscore.raw;
 
-import edu.wpi.cscore.CameraServerJNI;
-import edu.wpi.cscore.ImageSink;
+import edu.wpi.first.cscore.CameraServerJNI;
+import edu.wpi.first.cscore.ImageSink;
 
 /**
  * A sink for user code to accept video frames as raw bytes.

cscore/src/main/java/edu/wpi/first/cscore/raw/RawSource.java

@@ -2,11 +2,11 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore.raw;
+package edu.wpi.first.cscore.raw;
 
-import edu.wpi.cscore.CameraServerJNI;
-import edu.wpi.cscore.ImageSource;
-import edu.wpi.cscore.VideoMode;
+import edu.wpi.first.cscore.CameraServerJNI;
+import edu.wpi.first.cscore.ImageSource;
+import edu.wpi.first.cscore.VideoMode;
 
 /**
  * A source for user code to provide video frames as raw bytes.

cscore/src/main/native/windows/UsbCameraImpl.cpp

@@ -293,32 +293,45 @@ void UsbCameraImpl::ProcessFrame(IMFSample* videoSample,
       return;
   }
 
-  bool lock2d = false;
   BYTE* ptr = NULL;
   LONG pitch = 0;
-  DWORD maxsize = 0, cursize = 0;
+  DWORD length = 0;
 
-  // "For 2-D buffers, the Lock2D method is more efficient than the Lock
-  // method" see IMFMediaBuffer::Lock method documentation:
-  // https://msdn.microsoft.com/en-us/library/windows/desktop/bb970366(v=vs.85).aspx
-  ComPtr<IMF2DBuffer> buffer2d;
-  DWORD memLength2d = 0;
-  if (true) {
-    buffer2d = buf.As<IMF2DBuffer>();
-    if (buffer2d) {
-      buffer2d->GetContiguousLength(&memLength2d);
-      if (SUCCEEDED(buffer2d->Lock2D(&ptr, &pitch))) {
-        lock2d = true;
+  // First try to access using Lock2DSize, then try Lock2D, then fallback
+  // https://docs.microsoft.com/en-us/windows/win32/api/mfobjects/nf-mfobjects-imfmediabuffer-lock
+
+  ComPtr<IMF2DBuffer> buffer2d = buf.As<IMF2DBuffer>();
+  if (buffer2d) {
+    BYTE* scanline0 = nullptr;
+    HRESULT result;
+    ComPtr<IMF2DBuffer2> buffer2d2 = buf.As<IMF2DBuffer2>();
+    if (buffer2d2) {
+      BYTE* datastart;
+      result = buffer2d2->Lock2DSize(MF2DBuffer_LockFlags_Read, &scanline0,
+                                     &pitch, &datastart, &length);
+    } else {
+      result = buffer2d->Lock2D(&scanline0, &pitch);
+    }
+    if (SUCCEEDED(result)) {
+      BOOL isContiguous;
+      if (pitch > 0 && SUCCEEDED(buffer2d->IsContiguousFormat(&isContiguous)) &&
+          isContiguous &&
+          (length || SUCCEEDED(buffer2d->GetContiguousLength(&length)))) {
+        // Use the buffer pointer.
+        ptr = scanline0;
+      } else {
+        // Release the buffer and fall back to Lock().
+        buffer2d->Unlock2D();
       }
     }
   }
   if (ptr == NULL) {
-    if (!SUCCEEDED(buf->Lock(&ptr, &maxsize, &cursize))) {
+    buffer2d = nullptr;
+    DWORD maxsize = 0;
+    if (!SUCCEEDED(buf->Lock(&ptr, &maxsize, &length))) {
       return;
     }
   }
-  if (!ptr)
-    return;
 
   cv::Mat tmpMat;
   std::unique_ptr<Image> dest;
@@ -328,7 +341,7 @@ void UsbCameraImpl::ProcessFrame(IMFSample* videoSample,
     case cs::VideoMode::PixelFormat::kMJPEG: {
       // Special case
       PutFrame(VideoMode::kMJPEG, mode.width, mode.height,
-               wpi::StringRef(reinterpret_cast<char*>(ptr), cursize),
+               wpi::StringRef(reinterpret_cast<char*>(ptr), length),
                wpi::Now());
       doFinalSet = false;
       break;
@@ -360,10 +373,11 @@ void UsbCameraImpl::ProcessFrame(IMFSample* videoSample,
     PutFrame(std::move(dest), wpi::Now());
   }
 
-  if (lock2d)
+  if (buffer2d) {
     buffer2d->Unlock2D();
-  else
+  } else {
     buf->Unlock();
+  }
 }
 
 LRESULT UsbCameraImpl::PumpMain(HWND hwnd, UINT uiMsg, WPARAM wParam,

cscore/src/test/java/edu/wpi/first/cscore/JNITest.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 import org.junit.jupiter.api.Test;
 

cscore/src/test/java/edu/wpi/first/cscore/UsbCameraTest.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package edu.wpi.cscore;
+package edu.wpi.first.cscore;
 
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTimeoutPreemptively;

glass/src/libnt/native/cpp/NetworkTables.cpp

@@ -741,30 +741,20 @@ void glass::DisplayNetworkTables(NetworkTablesModel* model,
   ImGui::Columns();
 }
 
-void NetworkTablesView::Display() {
-  auto& storage = GetStorage();
-  auto pTreeView =
-      storage.GetBoolRef("tree", m_defaultFlags & NetworkTablesFlags_TreeView);
-  auto pShowConnections = storage.GetBoolRef(
-      "connections", m_defaultFlags & NetworkTablesFlags_ShowConnections);
-  auto pShowFlags = storage.GetBoolRef(
-      "flags", m_defaultFlags & NetworkTablesFlags_ShowFlags);
-  auto pShowTimestamp = storage.GetBoolRef(
-      "timestamp", m_defaultFlags & NetworkTablesFlags_ShowTimestamp);
-  auto pCreateNoncanonicalKeys = storage.GetBoolRef(
-      "createNonCanonical",
-      m_defaultFlags & NetworkTablesFlags_CreateNoncanonicalKeys);
-
-  if (ImGui::BeginPopupContextItem()) {
-    ImGui::MenuItem("Tree View", "", pTreeView);
-    ImGui::MenuItem("Show Connections", "", pShowConnections);
-    ImGui::MenuItem("Show Flags", "", pShowFlags);
-    ImGui::MenuItem("Show Timestamp", "", pShowTimestamp);
-    ImGui::Separator();
-    ImGui::MenuItem("Allow creation of non-canonical keys", "",
-                    pCreateNoncanonicalKeys);
-
-    ImGui::EndPopup();
+void NetworkTablesFlagsSettings::Update() {
+  if (!m_pTreeView) {
+    auto& storage = GetStorage();
+    m_pTreeView = storage.GetBoolRef(
+        "tree", m_defaultFlags & NetworkTablesFlags_TreeView);
+    m_pShowConnections = storage.GetBoolRef(
+        "connections", m_defaultFlags & NetworkTablesFlags_ShowConnections);
+    m_pShowFlags = storage.GetBoolRef(
+        "flags", m_defaultFlags & NetworkTablesFlags_ShowFlags);
+    m_pShowTimestamp = storage.GetBoolRef(
+        "timestamp", m_defaultFlags & NetworkTablesFlags_ShowTimestamp);
+    m_pCreateNoncanonicalKeys = storage.GetBoolRef(
+        "createNonCanonical",
+        m_defaultFlags & NetworkTablesFlags_CreateNoncanonicalKeys);
   }
 
   m_flags &=
@@ -772,11 +762,32 @@ void NetworkTablesView::Display() {
         NetworkTablesFlags_ShowFlags | NetworkTablesFlags_ShowTimestamp |
         NetworkTablesFlags_CreateNoncanonicalKeys);
   m_flags |=
-      (*pTreeView ? NetworkTablesFlags_TreeView : 0) |
-      (*pShowConnections ? NetworkTablesFlags_ShowConnections : 0) |
-      (*pShowFlags ? NetworkTablesFlags_ShowFlags : 0) |
-      (*pShowTimestamp ? NetworkTablesFlags_ShowTimestamp : 0) |
-      (*pCreateNoncanonicalKeys ? NetworkTablesFlags_CreateNoncanonicalKeys
-                                : 0);
-  DisplayNetworkTables(m_model, m_flags);
+      (*m_pTreeView ? NetworkTablesFlags_TreeView : 0) |
+      (*m_pShowConnections ? NetworkTablesFlags_ShowConnections : 0) |
+      (*m_pShowFlags ? NetworkTablesFlags_ShowFlags : 0) |
+      (*m_pShowTimestamp ? NetworkTablesFlags_ShowTimestamp : 0) |
+      (*m_pCreateNoncanonicalKeys ? NetworkTablesFlags_CreateNoncanonicalKeys
+                                  : 0);
+}
+
+void NetworkTablesFlagsSettings::DisplayMenu() {
+  if (!m_pTreeView) {
+    return;
+  }
+  ImGui::MenuItem("Tree View", "", m_pTreeView);
+  ImGui::MenuItem("Show Connections", "", m_pShowConnections);
+  ImGui::MenuItem("Show Flags", "", m_pShowFlags);
+  ImGui::MenuItem("Show Timestamp", "", m_pShowTimestamp);
+  ImGui::Separator();
+  ImGui::MenuItem("Allow creation of non-canonical keys", "",
+                  m_pCreateNoncanonicalKeys);
+}
+
+void NetworkTablesView::Display() {
+  m_flags.Update();
+  if (ImGui::BeginPopupContextItem()) {
+    m_flags.DisplayMenu();
+    ImGui::EndPopup();
+  }
+  DisplayNetworkTables(m_model, m_flags.GetFlags());
 }

glass/src/libnt/native/include/glass/networktables/NetworkTables.h

@@ -104,19 +104,39 @@ void DisplayNetworkTables(
     NetworkTablesModel* model,
     NetworkTablesFlags flags = NetworkTablesFlags_Default);
 
+class NetworkTablesFlagsSettings {
+ public:
+  explicit NetworkTablesFlagsSettings(
+      NetworkTablesFlags defaultFlags = NetworkTablesFlags_Default)
+      : m_defaultFlags{defaultFlags}, m_flags{defaultFlags} {}
+
+  void Update();
+  void DisplayMenu();
+
+  NetworkTablesFlags GetFlags() const { return m_flags; }
+
+ private:
+  bool* m_pTreeView = nullptr;
+  bool* m_pShowConnections = nullptr;
+  bool* m_pShowFlags = nullptr;
+  bool* m_pShowTimestamp = nullptr;
+  bool* m_pCreateNoncanonicalKeys = nullptr;
+  NetworkTablesFlags m_defaultFlags;  // NOLINT
+  NetworkTablesFlags m_flags;         // NOLINT
+};
+
 class NetworkTablesView : public View {
  public:
   explicit NetworkTablesView(
       NetworkTablesModel* model,
       NetworkTablesFlags defaultFlags = NetworkTablesFlags_Default)
-      : m_model{model}, m_defaultFlags{defaultFlags}, m_flags{defaultFlags} {}
+      : m_model{model}, m_flags{defaultFlags} {}
 
   void Display() override;
 
  private:
   NetworkTablesModel* m_model;
-  NetworkTablesFlags m_defaultFlags;
-  NetworkTablesFlags m_flags;
+  NetworkTablesFlagsSettings m_flags;
 };
 
 }  // namespace glass

hal/src/main/java/edu/wpi/first/hal/HAL.java

@@ -28,7 +28,36 @@ public final class HAL extends JNIWrapper {
 
   private static native void simPeriodicBeforeNative();
 
-  public static final List<Runnable> s_simPeriodicBefore = new ArrayList<>();
+  private static final List<Runnable> s_simPeriodicBefore = new ArrayList<>();
+
+  public static class SimPeriodicBeforeCallback implements AutoCloseable {
+    private SimPeriodicBeforeCallback(Runnable r) {
+      m_run = r;
+    }
+
+    @Override
+    public void close() {
+      synchronized (s_simPeriodicBefore) {
+        s_simPeriodicBefore.remove(m_run);
+      }
+    }
+
+    private final Runnable m_run;
+  }
+
+  /**
+   * Registers a callback to be run by IterativeRobotBase prior to the user's simulationPeriodic
+   * code.
+   *
+   * @param r runnable
+   * @return Callback object (must be retained for callback to stay active).
+   */
+  public static SimPeriodicBeforeCallback registerSimPeriodicBeforeCallback(Runnable r) {
+    synchronized (s_simPeriodicBefore) {
+      s_simPeriodicBefore.add(r);
+    }
+    return new SimPeriodicBeforeCallback(r);
+  }
 
   /**
    * Runs SimPeriodicBefore callbacks. IterativeRobotBase calls this prior to the user's
@@ -45,7 +74,35 @@ public final class HAL extends JNIWrapper {
 
   private static native void simPeriodicAfterNative();
 
-  public static final List<Runnable> s_simPeriodicAfter = new ArrayList<>();
+  private static final List<Runnable> s_simPeriodicAfter = new ArrayList<>();
+
+  public static class SimPeriodicAfterCallback implements AutoCloseable {
+    private SimPeriodicAfterCallback(Runnable r) {
+      m_run = r;
+    }
+
+    @Override
+    public void close() {
+      synchronized (s_simPeriodicAfter) {
+        s_simPeriodicAfter.remove(m_run);
+      }
+    }
+
+    private final Runnable m_run;
+  }
+
+  /**
+   * Registers a callback to be run by IterativeRobotBase after the user's simulationPeriodic code.
+   *
+   * @param r runnable
+   * @return Callback object (must be retained for callback to stay active).
+   */
+  public static SimPeriodicAfterCallback registerSimPeriodicAfterCallback(Runnable r) {
+    synchronized (s_simPeriodicAfter) {
+      s_simPeriodicAfter.add(r);
+    }
+    return new SimPeriodicAfterCallback(r);
+  }
 
   /**
    * Runs SimPeriodicAfter callbacks. IterativeRobotBase calls this after the user's

hal/src/main/java/edu/wpi/first/hal/simulation/SimDeviceDataJNI.java

@@ -47,17 +47,11 @@ public class SimDeviceDataJNI extends JNIWrapper {
   public static native int registerSimValueCreatedCallback(
       int device, SimValueCallback callback, boolean initialNotify);
 
-  public static native int registerSimValueCreatedCallback2(
-      int device, SimValueCallback2 callback, boolean initialNotify);
-
   public static native void cancelSimValueCreatedCallback(int uid);
 
   public static native int registerSimValueChangedCallback(
       int handle, SimValueCallback callback, boolean initialNotify);
 
-  public static native int registerSimValueChangedCallback2(
-      int handle, SimValueCallback2 callback, boolean initialNotify);
-
   public static native void cancelSimValueChangedCallback(int uid);
 
   /**
@@ -69,7 +63,7 @@ public class SimDeviceDataJNI extends JNIWrapper {
    * @param initialNotify ignored (present for consistency)
    */
   public static native int registerSimValueResetCallback(
-      int handle, SimValueCallback2 callback, boolean initialNotify);
+      int handle, SimValueCallback callback, boolean initialNotify);
 
   public static native void cancelSimValueResetCallback(int uid);
 

hal/src/main/java/edu/wpi/first/hal/simulation/SimValueCallback.java

@@ -8,10 +8,10 @@ import edu.wpi.first.hal.HALValue;
 
 @FunctionalInterface
 public interface SimValueCallback {
-  void callback(String name, int handle, boolean readonly, HALValue value);
+  void callback(String name, int handle, int direction, HALValue value);
 
   default void callbackNative(
-      String name, int handle, boolean readonly, int type, long value1, double value2) {
-    callback(name, handle, readonly, HALValue.fromNative(type, value1, value2));
+      String name, int handle, int direction, int type, long value1, double value2) {
+    callback(name, handle, direction, HALValue.fromNative(type, value1, value2));
   }
 }

hal/src/main/java/edu/wpi/first/hal/simulation/SimValueCallback2.java

@@ -1,17 +0,0 @@
-// Copyright (c) FIRST and other WPILib contributors.
-// Open Source Software; you can modify and/or share it under the terms of
-// the WPILib BSD license file in the root directory of this project.
-
-package edu.wpi.first.hal.simulation;
-
-import edu.wpi.first.hal.HALValue;
-
-@FunctionalInterface
-public interface SimValueCallback2 {
-  void callback(String name, int handle, int direction, HALValue value);
-
-  default void callbackNative(
-      String name, int handle, int direction, int type, long value1, double value2) {
-    callback(name, handle, direction, HALValue.fromNative(type, value1, value2));
-  }
-}

hal/src/main/java/edu/wpi/first/hal/simulation/SimulatorJNI.java

@@ -4,7 +4,6 @@
 
 package edu.wpi.first.hal.simulation;
 
-import edu.wpi.first.hal.HAL;
 import edu.wpi.first.hal.JNIWrapper;
 
 public class SimulatorJNI extends JNIWrapper {
@@ -29,48 +28,4 @@ public class SimulatorJNI extends JNIWrapper {
   public static native void stepTimingAsync(long delta);
 
   public static native void resetHandles();
-
-  public static class SimPeriodicBeforeCallback implements AutoCloseable {
-    private SimPeriodicBeforeCallback(Runnable r) {
-      m_run = r;
-    }
-
-    @Override
-    public void close() {
-      synchronized (HAL.s_simPeriodicBefore) {
-        HAL.s_simPeriodicBefore.remove(m_run);
-      }
-    }
-
-    private Runnable m_run;
-  }
-
-  public static SimPeriodicBeforeCallback registerSimPeriodicBeforeCallback(Runnable r) {
-    synchronized (HAL.s_simPeriodicBefore) {
-      HAL.s_simPeriodicBefore.add(r);
-    }
-    return new SimPeriodicBeforeCallback(r);
-  }
-
-  public static class SimPeriodicAfterCallback implements AutoCloseable {
-    private SimPeriodicAfterCallback(Runnable r) {
-      m_run = r;
-    }
-
-    @Override
-    public void close() {
-      synchronized (HAL.s_simPeriodicAfter) {
-        HAL.s_simPeriodicAfter.remove(m_run);
-      }
-    }
-
-    private Runnable m_run;
-  }
-
-  public static SimPeriodicAfterCallback registerSimPeriodicAfterCallback(Runnable r) {
-    synchronized (HAL.s_simPeriodicAfter) {
-      HAL.s_simPeriodicAfter.add(r);
-    }
-    return new SimPeriodicAfterCallback(r);
-  }
 }

hal/src/main/native/athena/AddressableLED.cpp

@@ -11,6 +11,7 @@
 #include "ConstantsInternal.h"
 #include "DigitalInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/AddressableLEDTypes.h"
 #include "hal/ChipObject.h"
@@ -142,8 +143,11 @@ void HAL_SetAddressableLEDLength(HAL_AddressableLEDHandle handle,
     return;
   }
 
-  if (length > HAL_kAddressableLEDMaxLength) {
+  if (length > HAL_kAddressableLEDMaxLength || length < 0) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status, "LED length must be less than or equal to " +
+                                  wpi::Twine(HAL_kAddressableLEDMaxLength) +
+                                  ". " + wpi::Twine(length) + " was requested");
     return;
   }
 
@@ -173,8 +177,11 @@ void HAL_WriteAddressableLEDData(HAL_AddressableLEDHandle handle,
     return;
   }
 
-  if (length > led->stringLength) {
+  if (length > led->stringLength || length < 0) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status, "Data length must be less than or equal to " +
+                                  wpi::Twine(led->stringLength) + ". " +
+                                  wpi::Twine(length) + " was requested");
     return;
   }
 

hal/src/main/native/athena/AnalogGyro.cpp

@@ -4,12 +4,14 @@
 
 #include "hal/AnalogGyro.h"
 
+#include <string>
 #include <thread>
 
 #include <wpi/raw_ostream.h>
 
 #include "AnalogInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "hal/AnalogAccumulator.h"
 #include "hal/AnalogInput.h"
 #include "hal/handles/IndexedHandleResource.h"
@@ -21,6 +23,7 @@ struct AnalogGyro {
   double voltsPerDegreePerSecond;
   double offset;
   int32_t center;
+  std::string previousAllocation;
 };
 
 }  // namespace
@@ -55,36 +58,43 @@ static void Wait(double seconds) {
 extern "C" {
 
 HAL_GyroHandle HAL_InitializeAnalogGyro(HAL_AnalogInputHandle analogHandle,
+                                        const char* allocationLocation,
                                         int32_t* status) {
   hal::init::CheckInit();
+  // Handle will be type checked by HAL_IsAccumulatorChannel
+  int16_t channel = getHandleIndex(analogHandle);
   if (!HAL_IsAccumulatorChannel(analogHandle, status)) {
     if (*status == 0) {
       *status = HAL_INVALID_ACCUMULATOR_CHANNEL;
+      hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for Analog Gyro",
+                                       0, kNumAccumulators, channel);
     }
     return HAL_kInvalidHandle;
   }
 
-  // handle known to be correct, so no need to type check
-  int16_t channel = getHandleIndex(analogHandle);
-
-  auto handle = analogGyroHandles->Allocate(channel, status);
+  HAL_GyroHandle handle;
+  auto gyro = analogGyroHandles->Allocate(channel, &handle, status);
 
   if (*status != 0) {
+    if (gyro) {
+      hal::SetLastErrorPreviouslyAllocated(status, "Analog Gyro", channel,
+                                           gyro->previousAllocation);
+    } else {
+      hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for Analog Gyro",
+                                       0, kNumAccumulators, channel);
+    }
     return HAL_kInvalidHandle;  // failed to allocate. Pass error back.
   }
 
   // Initialize port structure
-  auto gyro = analogGyroHandles->Get(handle);
-  if (gyro == nullptr) {  // would only error on thread issue
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
 
   gyro->handle = analogHandle;
   gyro->voltsPerDegreePerSecond = 0;
   gyro->offset = 0;
   gyro->center = 0;
 
+  gyro->previousAllocation = allocationLocation ? allocationLocation : "";
+
   return handle;
 }
 

hal/src/main/native/athena/AnalogInput.cpp

@@ -9,6 +9,7 @@
 
 #include "AnalogInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/AnalogAccumulator.h"
 #include "hal/handles/HandlesInternal.h"
@@ -21,8 +22,9 @@ using namespace hal;
 
 extern "C" {
 
-HAL_AnalogInputHandle HAL_InitializeAnalogInputPort(HAL_PortHandle portHandle,
-                                                    int32_t* status) {
+HAL_AnalogInputHandle HAL_InitializeAnalogInputPort(
+    HAL_PortHandle portHandle, const char* allocationLocation,
+    int32_t* status) {
   hal::init::CheckInit();
   initializeAnalog(status);
 
@@ -31,23 +33,28 @@ HAL_AnalogInputHandle HAL_InitializeAnalogInputPort(HAL_PortHandle portHandle,
   }
 
   int16_t channel = getPortHandleChannel(portHandle);
-  if (channel == InvalidHandleIndex) {
-    *status = PARAMETER_OUT_OF_RANGE;
+  if (channel == InvalidHandleIndex || channel >= kNumAnalogInputs) {
+    *status = RESOURCE_OUT_OF_RANGE;
+    hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for Analog Input",
+                                     0, kNumAnalogInputs, channel);
     return HAL_kInvalidHandle;
   }
 
-  HAL_AnalogInputHandle handle = analogInputHandles->Allocate(channel, status);
+  HAL_AnalogInputHandle handle;
+  auto analog_port = analogInputHandles->Allocate(channel, &handle, status);
 
   if (*status != 0) {
+    if (analog_port) {
+      hal::SetLastErrorPreviouslyAllocated(status, "Analog Input", channel,
+                                           analog_port->previousAllocation);
+    } else {
+      hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for Analog Input",
+                                       0, kNumAnalogInputs, channel);
+    }
     return HAL_kInvalidHandle;  // failed to allocate. Pass error back.
   }
 
   // Initialize port structure
-  auto analog_port = analogInputHandles->Get(handle);
-  if (analog_port == nullptr) {  // would only error on thread issue
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
   analog_port->channel = static_cast<uint8_t>(channel);
   if (HAL_IsAccumulatorChannel(handle, status)) {
     analog_port->accumulator.reset(tAccumulator::create(channel, status));
@@ -59,6 +66,8 @@ HAL_AnalogInputHandle HAL_InitializeAnalogInputPort(HAL_PortHandle portHandle,
   analogInputSystem->writeScanList(channel, channel, status);
   HAL_SetAnalogAverageBits(handle, kDefaultAverageBits, status);
   HAL_SetAnalogOversampleBits(handle, kDefaultOversampleBits, status);
+  analog_port->previousAllocation =
+      allocationLocation ? allocationLocation : "";
   return handle;
 }
 

hal/src/main/native/athena/AnalogInternal.h

@@ -7,6 +7,7 @@
 #include <stdint.h>
 
 #include <memory>
+#include <string>
 
 #include <wpi/mutex.h>
 
@@ -31,6 +32,7 @@ extern bool analogSampleRateSet;
 struct AnalogPort {
   uint8_t channel;
   std::unique_ptr<tAccumulator> accumulator;
+  std::string previousAllocation;
 };
 
 extern IndexedHandleResource<HAL_AnalogInputHandle, hal::AnalogPort,

hal/src/main/native/athena/AnalogOutput.cpp

@@ -4,8 +4,11 @@
 
 #include "hal/AnalogOutput.h"
 
+#include <string>
+
 #include "AnalogInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/Errors.h"
 #include "hal/handles/HandlesInternal.h"
@@ -17,6 +20,7 @@ namespace {
 
 struct AnalogOutput {
   uint8_t channel;
+  std::string previousAllocation;
 };
 
 }  // namespace
@@ -36,8 +40,9 @@ void InitializeAnalogOutput() {
 
 extern "C" {
 
-HAL_AnalogOutputHandle HAL_InitializeAnalogOutputPort(HAL_PortHandle portHandle,
-                                                      int32_t* status) {
+HAL_AnalogOutputHandle HAL_InitializeAnalogOutputPort(
+    HAL_PortHandle portHandle, const char* allocationLocation,
+    int32_t* status) {
   hal::init::CheckInit();
   initializeAnalog(status);
 
@@ -46,25 +51,31 @@ HAL_AnalogOutputHandle HAL_InitializeAnalogOutputPort(HAL_PortHandle portHandle,
   }
 
   int16_t channel = getPortHandleChannel(portHandle);
-  if (channel == InvalidHandleIndex) {
-    *status = PARAMETER_OUT_OF_RANGE;
+  if (channel == InvalidHandleIndex || channel >= kNumAnalogOutputs) {
+    *status = RESOURCE_OUT_OF_RANGE;
+    hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for Analog Output",
+                                     0, kNumAnalogOutputs, channel);
     return HAL_kInvalidHandle;
   }
 
-  HAL_AnalogOutputHandle handle =
-      analogOutputHandles->Allocate(channel, status);
+  HAL_AnalogOutputHandle handle;
+  auto port = analogOutputHandles->Allocate(channel, &handle, status);
 
   if (*status != 0) {
+    if (port) {
+      hal::SetLastErrorPreviouslyAllocated(status, "Analog Output", channel,
+                                           port->previousAllocation);
+    } else {
+      hal::SetLastErrorIndexOutOfRange(status,
+                                       "Invalid Index for Analog Output", 0,
+                                       kNumAnalogOutputs, channel);
+    }
     return HAL_kInvalidHandle;  // failed to allocate. Pass error back.
   }
 
-  auto port = analogOutputHandles->Get(handle);
-  if (port == nullptr) {  // would only error on thread issue
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
-
   port->channel = static_cast<uint8_t>(channel);
+  port->previousAllocation = allocationLocation ? allocationLocation : "";
+
   return handle;
 }
 

hal/src/main/native/athena/AnalogTrigger.cpp

@@ -7,6 +7,7 @@
 #include "AnalogInternal.h"
 #include "DutyCycleInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/AnalogInput.h"
 #include "hal/DutyCycle.h"
@@ -138,6 +139,11 @@ void HAL_SetAnalogTriggerLimitsDutyCycle(
 
   if (lower < 0.0 || upper > 1.0) {
     *status = PARAMETER_OUT_OF_RANGE;
+    auto lowerStr = std::to_string(lower);
+    auto upperStr = std::to_string(upper);
+    hal::SetLastError(
+        status, "Lower must be >= 0 and upper must be <=1. Requested lower " +
+                    lowerStr + " Requested upper " + upperStr);
     return;
   }
 

hal/src/main/native/athena/Counter.cpp

@@ -7,6 +7,7 @@
 #include "ConstantsInternal.h"
 #include "DigitalInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/HAL.h"
 #include "hal/handles/LimitedHandleResource.h"
@@ -146,6 +147,9 @@ void HAL_SetCounterDownSource(HAL_CounterHandle counterHandle,
     // TODO: wpi_setWPIErrorWithContext(ParameterOutOfRange, "Counter only
     // supports DownSource in TwoPulse and ExternalDirection modes.");
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status,
+                      "Counter only supports DownSource in TwoPulse and "
+                      "ExternalDirection mode.");
     return;
   }
 
@@ -260,6 +264,11 @@ void HAL_SetCounterSamplesToAverage(HAL_CounterHandle counterHandle,
   }
   if (samplesToAverage < 1 || samplesToAverage > 127) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(
+        status,
+        "Samples to average must be between 1 and 127 inclusive. Requested " +
+            wpi::Twine(samplesToAverage));
+    return;
   }
   counter->counter->writeTimerConfig_AverageSize(samplesToAverage, status);
 }

hal/src/main/native/athena/DIO.cpp

@@ -11,6 +11,7 @@
 
 #include "DigitalInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/cpp/fpga_clock.h"
 #include "hal/handles/HandlesInternal.h"
@@ -38,7 +39,9 @@ void InitializeDIO() {
 extern "C" {
 
 HAL_DigitalHandle HAL_InitializeDIOPort(HAL_PortHandle portHandle,
-                                        HAL_Bool input, int32_t* status) {
+                                        HAL_Bool input,
+                                        const char* allocationLocation,
+                                        int32_t* status) {
   hal::init::CheckInit();
   initializeDigital(status);
 
@@ -48,23 +51,28 @@ HAL_DigitalHandle HAL_InitializeDIOPort(HAL_PortHandle portHandle,
 
   int16_t channel = getPortHandleChannel(portHandle);
   if (channel == InvalidHandleIndex || channel >= kNumDigitalChannels) {
-    *status = PARAMETER_OUT_OF_RANGE;
+    *status = RESOURCE_OUT_OF_RANGE;
+    hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for DIO", 0,
+                                     kNumDigitalChannels, channel);
     return HAL_kInvalidHandle;
   }
 
-  auto handle =
-      digitalChannelHandles->Allocate(channel, HAL_HandleEnum::DIO, status);
+  HAL_DigitalHandle handle;
+
+  auto port = digitalChannelHandles->Allocate(channel, HAL_HandleEnum::DIO,
+                                              &handle, status);
 
   if (*status != 0) {
+    if (port) {
+      hal::SetLastErrorPreviouslyAllocated(status, "PWM or DIO", channel,
+                                           port->previousAllocation);
+    } else {
+      hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for DIO", 0,
+                                       kNumDigitalChannels, channel);
+    }
     return HAL_kInvalidHandle;  // failed to allocate. Pass error back.
   }
 
-  auto port = digitalChannelHandles->Get(handle, HAL_HandleEnum::DIO);
-  if (port == nullptr) {  // would only occur on thread issue.
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
-
   port->channel = static_cast<uint8_t>(channel);
 
   std::scoped_lock lock(digitalDIOMutex);
@@ -114,6 +122,7 @@ HAL_DigitalHandle HAL_InitializeDIOPort(HAL_PortHandle portHandle,
   }
 
   digitalSystem->writeOutputEnable(outputEnable, status);
+  port->previousAllocation = allocationLocation ? allocationLocation : "";
 
   return handle;
 }
@@ -191,8 +200,8 @@ void HAL_SetDigitalPWMRate(double rate, int32_t* status) {
   if (*status != 0) {
     return;
   }
-  uint16_t pwmPeriodPower = static_cast<uint16_t>(
-      std::log(1.0 / (16 * 1.0E-6 * rate)) / std::log(2.0) + 0.5);
+  uint16_t pwmPeriodPower =
+      std::lround(std::log(1.0 / (16 * 1.0E-6 * rate)) / std::log(2.0));
   digitalSystem->writePWMPeriodPower(pwmPeriodPower, status);
 }
 

hal/src/main/native/athena/DMA.cpp

@@ -13,6 +13,7 @@
 #include "AnalogInternal.h"
 #include "DigitalInternal.h"
 #include "EncoderInternal.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/AnalogAccumulator.h"
 #include "hal/AnalogGyro.h"
@@ -528,6 +529,9 @@ void HAL_SetDMAExternalTrigger(HAL_DMAHandle handle,
 
   if (!success) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status,
+                      "Digital Source unabled to be mapped properly. Likely "
+                      "invalid handle passed.");
     return;
   }
 

hal/src/main/native/athena/DigitalInternal.cpp

@@ -5,6 +5,7 @@
 #include "DigitalInternal.h"
 
 #include <atomic>
+#include <cmath>
 #include <thread>
 
 #include <FRC_NetworkCommunication/LoadOut.h>
@@ -108,10 +109,10 @@ void initializeDigital(int32_t* status) {
   double loopTime = pwmSystem->readLoopTiming(status) /
                     (kSystemClockTicksPerMicrosecond * 1e3);
 
-  pwmSystem->writeConfig_Period(
-      static_cast<uint16_t>(kDefaultPwmPeriod / loopTime + 0.5), status);
-  uint16_t minHigh = static_cast<uint16_t>(
-      (kDefaultPwmCenter - kDefaultPwmStepsDown * loopTime) / loopTime + 0.5);
+  pwmSystem->writeConfig_Period(std::lround(kDefaultPwmPeriod / loopTime),
+                                status);
+  uint16_t minHigh = std::lround(
+      (kDefaultPwmCenter - kDefaultPwmStepsDown * loopTime) / loopTime);
   pwmSystem->writeConfig_MinHigh(minHigh, status);
   // Ensure that PWM output values are set to OFF
   for (uint8_t pwmIndex = 0; pwmIndex < kNumPWMChannels; pwmIndex++) {

hal/src/main/native/athena/DigitalInternal.h

@@ -7,6 +7,7 @@
 #include <stdint.h>
 
 #include <memory>
+#include <string>
 
 #include <wpi/mutex.h>
 
@@ -70,6 +71,7 @@ struct DigitalPort {
   int32_t centerPwm = 0;
   int32_t deadbandMinPwm = 0;
   int32_t minPwm = 0;
+  std::string previousAllocation;
 };
 
 extern DigitalHandleResource<HAL_DigitalHandle, DigitalPort,

hal/src/main/native/athena/Encoder.cpp

@@ -7,6 +7,7 @@
 #include "EncoderInternal.h"
 #include "FPGAEncoder.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/ChipObject.h"
 #include "hal/Counter.h"
@@ -46,6 +47,9 @@ Encoder::Encoder(HAL_Handle digitalSourceHandleA,
     }
     default:
       *status = PARAMETER_OUT_OF_RANGE;
+      hal::SetLastError(status, "Encoding type " +
+                                    wpi::Twine(static_cast<int>(encodingType)) +
+                                    " invalid.");
       return;
   }
 }
@@ -181,6 +185,10 @@ void Encoder::SetReverseDirection(bool reverseDirection, int32_t* status) {
 void Encoder::SetSamplesToAverage(int32_t samplesToAverage, int32_t* status) {
   if (samplesToAverage < 1 || samplesToAverage > 127) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(
+        status,
+        "Samples to average must be between 1 and 127 inclusive. Requested " +
+            wpi::Twine(samplesToAverage));
     return;
   }
   if (m_counter) {

hal/src/main/native/athena/FPGAEncoder.cpp

@@ -8,6 +8,7 @@
 
 #include "DigitalInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/handles/LimitedHandleResource.h"
 
@@ -193,6 +194,11 @@ void HAL_SetFPGAEncoderSamplesToAverage(HAL_FPGAEncoderHandle fpgaEncoderHandle,
   }
   if (samplesToAverage < 1 || samplesToAverage > 127) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(
+        status,
+        "Samples to average must be between 1 and 127 inclusive. Requested " +
+            wpi::Twine(samplesToAverage));
+    return;
   }
   encoder->encoder->writeTimerConfig_AverageSize(samplesToAverage, status);
 }

hal/src/main/native/athena/HAL.cpp

@@ -233,6 +233,8 @@ const char* HAL_GetErrorMessage(int32_t code) {
       return HAL_CAN_BUFFER_OVERRUN_MESSAGE;
     case HAL_LED_CHANNEL_ERROR:
       return HAL_LED_CHANNEL_ERROR_MESSAGE;
+    case HAL_USE_LAST_ERROR:
+      return HAL_USE_LAST_ERROR_MESSAGE;
     default:
       return "Unknown error status";
   }

hal/src/main/native/athena/HALInternal.h

@@ -6,7 +6,15 @@
 
 #include <stdint.h>
 
+#include <wpi/Twine.h>
+
 namespace hal {
 void ReleaseFPGAInterrupt(int32_t interruptNumber);
-
+void SetLastError(int32_t* status, const wpi::Twine& value);
+void SetLastErrorIndexOutOfRange(int32_t* status, const wpi::Twine& message,
+                                 int32_t minimum, int32_t maximum,
+                                 int32_t channel);
+void SetLastErrorPreviouslyAllocated(int32_t* status, const wpi::Twine& message,
+                                     int32_t channel,
+                                     const wpi::Twine& previousAllocation);
 }  // namespace hal

hal/src/main/native/athena/I2C.cpp

@@ -67,11 +67,11 @@ void HAL_InitializeI2C(HAL_I2CPort port, int32_t* status) {
       return;
     }
     if ((i2CMXPDigitalHandle1 = HAL_InitializeDIOPort(
-             HAL_GetPort(24), false, status)) == HAL_kInvalidHandle) {
+             HAL_GetPort(24), false, nullptr, status)) == HAL_kInvalidHandle) {
       return;
     }
     if ((i2CMXPDigitalHandle2 = HAL_InitializeDIOPort(
-             HAL_GetPort(25), false, status)) == HAL_kInvalidHandle) {
+             HAL_GetPort(25), false, nullptr, status)) == HAL_kInvalidHandle) {
       HAL_FreeDIOPort(i2CMXPDigitalHandle1);  // free the first port allocated
       return;
     }

hal/src/main/native/athena/PDP.cpp

@@ -7,6 +7,7 @@
 #include <wpi/mutex.h>
 
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/CANAPI.h"
 #include "hal/Errors.h"
@@ -117,6 +118,7 @@ HAL_PDPHandle HAL_InitializePDP(int32_t module, int32_t* status) {
   hal::init::CheckInit();
   if (!HAL_CheckPDPModule(module)) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status, "Invalid pdp module " + wpi::Twine(module));
     return HAL_kInvalidHandle;
   }
 
@@ -192,6 +194,7 @@ double HAL_GetPDPChannelCurrent(HAL_PDPHandle handle, int32_t channel,
                                 int32_t* status) {
   if (!HAL_CheckPDPChannel(channel)) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status, "Invalid pdp channel " + wpi::Twine(channel));
     return 0;
   }
 

hal/src/main/native/athena/PWM.cpp

@@ -12,6 +12,7 @@
 #include "ConstantsInternal.h"
 #include "DigitalInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/cpp/fpga_clock.h"
 #include "hal/handles/HandlesInternal.h"
@@ -65,6 +66,7 @@ void InitializePWM() {}
 extern "C" {
 
 HAL_DigitalHandle HAL_InitializePWMPort(HAL_PortHandle portHandle,
+                                        const char* allocationLocation,
                                         int32_t* status) {
   hal::init::CheckInit();
   initializeDigital(status);
@@ -75,7 +77,9 @@ HAL_DigitalHandle HAL_InitializePWMPort(HAL_PortHandle portHandle,
 
   int16_t channel = getPortHandleChannel(portHandle);
   if (channel == InvalidHandleIndex || channel >= kNumPWMChannels) {
-    *status = PARAMETER_OUT_OF_RANGE;
+    *status = RESOURCE_OUT_OF_RANGE;
+    hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for PWM", 0,
+                                     kNumPWMChannels, channel);
     return HAL_kInvalidHandle;
   }
 
@@ -87,19 +91,22 @@ HAL_DigitalHandle HAL_InitializePWMPort(HAL_PortHandle portHandle,
     channel = remapMXPPWMChannel(channel) + 10;  // remap MXP to proper channel
   }
 
-  auto handle =
-      digitalChannelHandles->Allocate(channel, HAL_HandleEnum::PWM, status);
+  HAL_DigitalHandle handle;
+
+  auto port = digitalChannelHandles->Allocate(channel, HAL_HandleEnum::PWM,
+                                              &handle, status);
 
   if (*status != 0) {
+    if (port) {
+      hal::SetLastErrorPreviouslyAllocated(status, "PWM or DIO", channel,
+                                           port->previousAllocation);
+    } else {
+      hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for PWM", 0,
+                                       kNumPWMChannels, channel);
+    }
     return HAL_kInvalidHandle;  // failed to allocate. Pass error back.
   }
 
-  auto port = digitalChannelHandles->Get(handle, HAL_HandleEnum::PWM);
-  if (port == nullptr) {  // would only occur on thread issue.
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
-
   port->channel = origChannel;
 
   if (port->channel > tPWM::kNumHdrRegisters - 1) {
@@ -113,6 +120,8 @@ HAL_DigitalHandle HAL_InitializePWMPort(HAL_PortHandle portHandle,
   // Defaults to allow an always valid config.
   HAL_SetPWMConfig(handle, 2.0, 1.501, 1.5, 1.499, 1.0, status);
 
+  port->previousAllocation = allocationLocation ? allocationLocation : "";
+
   return handle;
 }
 void HAL_FreePWMPort(HAL_DigitalHandle pwmPortHandle, int32_t* status) {
@@ -277,13 +286,13 @@ void HAL_SetPWMSpeed(HAL_DigitalHandle pwmPortHandle, double speed,
   if (speed == 0.0) {
     rawValue = GetCenterPwm(dPort);
   } else if (speed > 0.0) {
-    rawValue = static_cast<int32_t>(
-        speed * static_cast<double>(GetPositiveScaleFactor(dPort)) +
-        static_cast<double>(GetMinPositivePwm(dPort)) + 0.5);
+    rawValue =
+        std::lround(speed * static_cast<double>(GetPositiveScaleFactor(dPort)) +
+                    static_cast<double>(GetMinPositivePwm(dPort)));
   } else {
-    rawValue = static_cast<int32_t>(
-        speed * static_cast<double>(GetNegativeScaleFactor(dPort)) +
-        static_cast<double>(GetMaxNegativePwm(dPort)) + 0.5);
+    rawValue =
+        std::lround(speed * static_cast<double>(GetNegativeScaleFactor(dPort)) +
+                    static_cast<double>(GetMaxNegativePwm(dPort)));
   }
 
   if (!((rawValue >= GetMinNegativePwm(dPort)) &&

hal/src/main/native/athena/Relay.cpp

@@ -4,8 +4,11 @@
 
 #include "hal/Relay.h"
 
+#include <string>
+
 #include "DigitalInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/handles/IndexedHandleResource.h"
 
@@ -16,6 +19,7 @@ namespace {
 struct Relay {
   uint8_t channel;
   bool fwd;
+  std::string previousAllocation;
 };
 
 }  // namespace
@@ -38,6 +42,7 @@ void InitializeRelay() {
 extern "C" {
 
 HAL_RelayHandle HAL_InitializeRelayPort(HAL_PortHandle portHandle, HAL_Bool fwd,
+                                        const char* allocationLocation,
                                         int32_t* status) {
   hal::init::CheckInit();
   initializeDigital(status);
@@ -47,8 +52,10 @@ HAL_RelayHandle HAL_InitializeRelayPort(HAL_PortHandle portHandle, HAL_Bool fwd,
   }
 
   int16_t channel = getPortHandleChannel(portHandle);
-  if (channel == InvalidHandleIndex) {
-    *status = PARAMETER_OUT_OF_RANGE;
+  if (channel == InvalidHandleIndex || channel >= kNumRelayChannels) {
+    *status = RESOURCE_OUT_OF_RANGE;
+    hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for Relay", 0,
+                                     kNumRelayChannels, channel);
     return HAL_kInvalidHandle;
   }
 
@@ -56,18 +63,20 @@ HAL_RelayHandle HAL_InitializeRelayPort(HAL_PortHandle portHandle, HAL_Bool fwd,
     channel += kNumRelayHeaders;  // add 4 to reverse channels
   }
 
-  auto handle = relayHandles->Allocate(channel, status);
+  HAL_RelayHandle handle;
+  auto port = relayHandles->Allocate(channel, &handle, status);
 
   if (*status != 0) {
+    if (port) {
+      hal::SetLastErrorPreviouslyAllocated(status, "Relay", channel,
+                                           port->previousAllocation);
+    } else {
+      hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for Relay", 0,
+                                       kNumRelayChannels, channel);
+    }
     return HAL_kInvalidHandle;  // failed to allocate. Pass error back.
   }
 
-  auto port = relayHandles->Get(handle);
-  if (port == nullptr) {  // would only occur on thread issue.
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
-
   if (!fwd) {
     // Subtract number of headers to put channel in range
     channel -= kNumRelayHeaders;
@@ -78,6 +87,7 @@ HAL_RelayHandle HAL_InitializeRelayPort(HAL_PortHandle portHandle, HAL_Bool fwd,
   }
 
   port->channel = static_cast<uint8_t>(channel);
+  port->previousAllocation = allocationLocation ? allocationLocation : "";
   return handle;
 }
 

hal/src/main/native/athena/SPI.cpp

@@ -18,6 +18,7 @@
 
 #include "DigitalInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "hal/DIO.h"
 #include "hal/HAL.h"
 #include "hal/handles/HandlesInternal.h"
@@ -75,14 +76,14 @@ static void CommonSPIPortInit(int32_t* status) {
     }
     // MISO
     if ((digitalHandles[3] = HAL_InitializeDIOPort(createPortHandleForSPI(29),
-                                                   false, status)) ==
+                                                   false, nullptr, status)) ==
         HAL_kInvalidHandle) {
       std::printf("Failed to allocate DIO 29 (MISO)\n");
       return;
     }
     // MOSI
     if ((digitalHandles[4] = HAL_InitializeDIOPort(createPortHandleForSPI(30),
-                                                   false, status)) ==
+                                                   false, nullptr, status)) ==
         HAL_kInvalidHandle) {
       std::printf("Failed to allocate DIO 30 (MOSI)\n");
       HAL_FreeDIOPort(digitalHandles[3]);  // free the first port allocated
@@ -103,6 +104,9 @@ void HAL_InitializeSPI(HAL_SPIPort port, int32_t* status) {
   hal::init::CheckInit();
   if (port < 0 || port >= kSpiMaxHandles) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status, "Serial port must be between 0 and " +
+                                  wpi::Twine(kSpiMaxHandles) + ". Requested " +
+                                  wpi::Twine(static_cast<int>(port)));
     return;
   }
 
@@ -133,7 +137,7 @@ void HAL_InitializeSPI(HAL_SPIPort port, int32_t* status) {
       }
       // CS1, Allocate
       if ((digitalHandles[0] = HAL_InitializeDIOPort(createPortHandleForSPI(26),
-                                                     false, status)) ==
+                                                     false, nullptr, status)) ==
           HAL_kInvalidHandle) {
         std::printf("Failed to allocate DIO 26 (CS1)\n");
         CommonSPIPortFree();
@@ -156,7 +160,7 @@ void HAL_InitializeSPI(HAL_SPIPort port, int32_t* status) {
       }
       // CS2, Allocate
       if ((digitalHandles[1] = HAL_InitializeDIOPort(createPortHandleForSPI(27),
-                                                     false, status)) ==
+                                                     false, nullptr, status)) ==
           HAL_kInvalidHandle) {
         std::printf("Failed to allocate DIO 27 (CS2)\n");
         CommonSPIPortFree();
@@ -179,7 +183,7 @@ void HAL_InitializeSPI(HAL_SPIPort port, int32_t* status) {
       }
       // CS3, Allocate
       if ((digitalHandles[2] = HAL_InitializeDIOPort(createPortHandleForSPI(28),
-                                                     false, status)) ==
+                                                     false, nullptr, status)) ==
           HAL_kInvalidHandle) {
         std::printf("Failed to allocate DIO 28 (CS3)\n");
         CommonSPIPortFree();
@@ -201,20 +205,20 @@ void HAL_InitializeSPI(HAL_SPIPort port, int32_t* status) {
         return;
       }
       if ((digitalHandles[5] = HAL_InitializeDIOPort(createPortHandleForSPI(14),
-                                                     false, status)) ==
+                                                     false, nullptr, status)) ==
           HAL_kInvalidHandle) {
         wpi::outs() << "Failed to allocate DIO 14\n";
         return;
       }
       if ((digitalHandles[6] = HAL_InitializeDIOPort(createPortHandleForSPI(15),
-                                                     false, status)) ==
+                                                     false, nullptr, status)) ==
           HAL_kInvalidHandle) {
         wpi::outs() << "Failed to allocate DIO 15\n";
         HAL_FreeDIOPort(digitalHandles[5]);  // free the first port allocated
         return;
       }
       if ((digitalHandles[7] = HAL_InitializeDIOPort(createPortHandleForSPI(16),
-                                                     false, status)) ==
+                                                     false, nullptr, status)) ==
           HAL_kInvalidHandle) {
         wpi::outs() << "Failed to allocate DIO 16\n";
         HAL_FreeDIOPort(digitalHandles[5]);  // free the first port allocated
@@ -222,7 +226,7 @@ void HAL_InitializeSPI(HAL_SPIPort port, int32_t* status) {
         return;
       }
       if ((digitalHandles[8] = HAL_InitializeDIOPort(createPortHandleForSPI(17),
-                                                     false, status)) ==
+                                                     false, nullptr, status)) ==
           HAL_kInvalidHandle) {
         wpi::outs() << "Failed to allocate DIO 17\n";
         HAL_FreeDIOPort(digitalHandles[5]);  // free the first port allocated
@@ -246,6 +250,8 @@ void HAL_InitializeSPI(HAL_SPIPort port, int32_t* status) {
       break;
     default:
       *status = PARAMETER_OUT_OF_RANGE;
+      hal::SetLastError(
+          status, "Invalid SPI port " + wpi::Twine(static_cast<int>(port)));
       break;
   }
 }
@@ -374,6 +380,9 @@ void HAL_SetSPIOpts(HAL_SPIPort port, HAL_Bool msbFirst,
 void HAL_SetSPIChipSelectActiveHigh(HAL_SPIPort port, int32_t* status) {
   if (port < 0 || port >= kSpiMaxHandles) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status, "Serial port must be between 0 and " +
+                                  wpi::Twine(kSpiMaxHandles) + ". Requested " +
+                                  wpi::Twine(static_cast<int>(port)));
     return;
   }
 
@@ -389,6 +398,9 @@ void HAL_SetSPIChipSelectActiveHigh(HAL_SPIPort port, int32_t* status) {
 void HAL_SetSPIChipSelectActiveLow(HAL_SPIPort port, int32_t* status) {
   if (port < 0 || port >= kSpiMaxHandles) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status, "Serial port must be between 0 and " +
+                                  wpi::Twine(kSpiMaxHandles) + ". Requested " +
+                                  wpi::Twine(static_cast<int>(port)));
     return;
   }
 
@@ -453,6 +465,9 @@ void HAL_SetSPIHandle(HAL_SPIPort port, int32_t handle) {
 void HAL_InitSPIAuto(HAL_SPIPort port, int32_t bufferSize, int32_t* status) {
   if (port < 0 || port >= kSpiMaxHandles) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status, "Serial port must be between 0 and " +
+                                  wpi::Twine(kSpiMaxHandles) + ". Requested " +
+                                  wpi::Twine(static_cast<int>(port)));
     return;
   }
 
@@ -484,6 +499,9 @@ void HAL_InitSPIAuto(HAL_SPIPort port, int32_t bufferSize, int32_t* status) {
 void HAL_FreeSPIAuto(HAL_SPIPort port, int32_t* status) {
   if (port < 0 || port >= kSpiMaxHandles) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status, "Serial port must be between 0 and " +
+                                  wpi::Twine(kSpiMaxHandles) + ". Requested " +
+                                  wpi::Twine(static_cast<int>(port)));
     return;
   }
 
@@ -586,11 +604,17 @@ void HAL_SetSPIAutoTransmitData(HAL_SPIPort port, const uint8_t* dataToSend,
                                 int32_t* status) {
   if (dataSize < 0 || dataSize > 32) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(
+        status, "Data size must be between 0 and 32 inclusive. Requested " +
+                    wpi::Twine(dataSize));
     return;
   }
 
   if (zeroSize < 0 || zeroSize > 127) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(
+        status, "Zero size must be between 0 and 127 inclusive. Requested " +
+                    wpi::Twine(zeroSize));
     return;
   }
 

hal/src/main/native/athena/SerialPort.cpp

@@ -19,6 +19,7 @@
 #include <string>
 #include <thread>
 
+#include "HALInternal.h"
 #include "hal/cpp/SerialHelper.h"
 #include "hal/handles/HandlesInternal.h"
 #include "hal/handles/IndexedHandleResource.h"
@@ -70,19 +71,14 @@ HAL_SerialPortHandle HAL_InitializeSerialPort(HAL_SerialPort port,
 HAL_SerialPortHandle HAL_InitializeSerialPortDirect(HAL_SerialPort port,
                                                     const char* portName,
                                                     int32_t* status) {
-  auto handle = serialPortHandles->Allocate(static_cast<int16_t>(port), status);
+  HAL_SerialPortHandle handle;
+  auto serialPort =
+      serialPortHandles->Allocate(static_cast<int16_t>(port), &handle, status);
 
   if (*status != 0) {
     return HAL_kInvalidHandle;
   }
 
-  auto serialPort = serialPortHandles->Get(handle);
-
-  if (serialPort == nullptr) {
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
-
   serialPort->portId = open(portName, O_RDWR | O_NOCTTY);
   if (serialPort->portId < 0) {
     *status = errno;
@@ -188,6 +184,7 @@ void HAL_SetSerialBaudRate(HAL_SerialPortHandle handle, int32_t baud,
     BAUDCASE(4000000)
     default:
       *status = PARAMETER_OUT_OF_RANGE;
+      hal::SetLastError(status, "Invalid BaudRate: " + wpi::Twine(baud));
       return;
   }
   int err = cfsetospeed(&port->tty, static_cast<speed_t>(port->baudRate));
@@ -230,6 +227,7 @@ void HAL_SetSerialDataBits(HAL_SerialPortHandle handle, int32_t bits,
       break;
     default:
       *status = PARAMETER_OUT_OF_RANGE;
+      hal::SetLastError(status, "Invalid data bits: " + wpi::Twine(bits));
       return;
   }
 
@@ -277,6 +275,7 @@ void HAL_SetSerialParity(HAL_SerialPortHandle handle, int32_t parity,
       break;
     default:
       *status = PARAMETER_OUT_OF_RANGE;
+      hal::SetLastError(status, "Invalid parity bits: " + wpi::Twine(parity));
       return;
   }
 
@@ -304,6 +303,7 @@ void HAL_SetSerialStopBits(HAL_SerialPortHandle handle, int32_t stopBits,
       break;
     default:
       *status = PARAMETER_OUT_OF_RANGE;
+      hal::SetLastError(status, "Invalid stop bits: " + wpi::Twine(stopBits));
       return;
   }
 
@@ -339,6 +339,7 @@ void HAL_SetSerialFlowControl(HAL_SerialPortHandle handle, int32_t flow,
       break;
     default:
       *status = PARAMETER_OUT_OF_RANGE;
+      hal::SetLastError(status, "Invalid fc bits: " + wpi::Twine(flow));
       return;
   }
 

hal/src/main/native/athena/Solenoid.cpp

@@ -60,16 +60,12 @@ HAL_SolenoidHandle HAL_InitializeSolenoidPort(HAL_PortHandle portHandle,
     return HAL_kInvalidHandle;
   }
 
-  auto handle = solenoidHandles->Allocate(
-      module * kNumSolenoidChannels + channel, status);
+  HAL_SolenoidHandle handle;
+  auto solenoidPort = solenoidHandles->Allocate(
+      module * kNumSolenoidChannels + channel, &handle, status);
   if (*status != 0) {
     return HAL_kInvalidHandle;
   }
-  auto solenoidPort = solenoidHandles->Get(handle);
-  if (solenoidPort == nullptr) {  // would only occur on thread issues
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
   solenoidPort->module = static_cast<uint8_t>(module);
   solenoidPort->channel = static_cast<uint8_t>(channel);
 

hal/src/main/native/cpp/ErrorHandling.cpp

@@ -0,0 +1,61 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include <wpi/SmallString.h>
+#include <wpi/Twine.h>
+
+#include "hal/Errors.h"
+#include "hal/HALBase.h"
+
+namespace {
+struct LastErrorStorage {
+  int32_t status;
+  wpi::SmallString<512> message;
+};
+}  // namespace
+
+static LastErrorStorage& GetThreadLastError() {
+  thread_local LastErrorStorage lastError;
+  return lastError;
+}
+
+namespace hal {
+void SetLastError(int32_t* status, const wpi::Twine& value) {
+  LastErrorStorage& lastError = GetThreadLastError();
+  lastError.message.clear();
+  value.toVector(lastError.message);
+  lastError.status = *status;
+  *status = HAL_USE_LAST_ERROR;
+}
+
+void SetLastErrorIndexOutOfRange(int32_t* status, const wpi::Twine& message,
+                                 int32_t minimum, int32_t maximum,
+                                 int32_t requested) {
+  SetLastError(status, message + "\n Status: " + wpi::Twine(*status) +
+                           "\n  Minimum: " + wpi::Twine(minimum) +
+                           " Maximum: " + wpi::Twine(maximum) +
+                           " Reequested: " + wpi::Twine(requested));
+}
+
+void SetLastErrorPreviouslyAllocated(int32_t* status, const wpi::Twine& message,
+                                     int32_t channel,
+                                     const wpi::Twine& previousAllocation) {
+  hal::SetLastError(
+      status,
+      message + " " + wpi::Twine(channel) +
+          " previously allocated.\nLocation of the previous allocation:\n" +
+          previousAllocation + "\nLocation of the current allocation:");
+}
+}  // namespace hal
+
+extern "C" {
+const char* HAL_GetLastError(int32_t* status) {
+  if (*status == HAL_USE_LAST_ERROR) {
+    LastErrorStorage& lastError = GetThreadLastError();
+    *status = lastError.status;
+    return lastError.message.c_str();
+  }
+  return HAL_GetErrorMessage(*status);
+}
+}  // extern "C"

hal/src/main/native/cpp/jni/AnalogGyroJNI.cpp

@@ -6,6 +6,8 @@
 
 #include <cassert>
 
+#include <wpi/jni_util.h>
+
 #include "HALUtil.h"
 #include "edu_wpi_first_hal_AnalogGyroJNI.h"
 #include "hal/AnalogGyro.h"
@@ -24,8 +26,9 @@ Java_edu_wpi_first_hal_AnalogGyroJNI_initializeAnalogGyro
   (JNIEnv* env, jclass, jint id)
 {
   int32_t status = 0;
-  HAL_GyroHandle handle =
-      HAL_InitializeAnalogGyro((HAL_AnalogInputHandle)id, &status);
+  auto stack = wpi::java::GetJavaStackTrace(env, "edu.wpi.first");
+  HAL_GyroHandle handle = HAL_InitializeAnalogGyro((HAL_AnalogInputHandle)id,
+                                                   stack.c_str(), &status);
   // Analog input does range checking, so we don't need to do so.
   CheckStatusForceThrow(env, status);
   return (jint)handle;

hal/src/main/native/cpp/jni/AnalogJNI.cpp

@@ -6,6 +6,8 @@
 
 #include <cassert>
 
+#include <wpi/jni_util.h>
+
 #include "HALUtil.h"
 #include "edu_wpi_first_hal_AnalogJNI.h"
 #include "hal/AnalogAccumulator.h"
@@ -29,9 +31,10 @@ Java_edu_wpi_first_hal_AnalogJNI_initializeAnalogInputPort
   (JNIEnv* env, jclass, jint id)
 {
   int32_t status = 0;
-  auto analog = HAL_InitializeAnalogInputPort((HAL_PortHandle)id, &status);
-  CheckStatusRange(env, status, 0, HAL_GetNumAnalogInputs(),
-                   hal::getPortHandleChannel((HAL_PortHandle)id));
+  auto stack = wpi::java::GetJavaStackTrace(env, "edu.wpi.first");
+  auto analog =
+      HAL_InitializeAnalogInputPort((HAL_PortHandle)id, stack.c_str(), &status);
+  CheckStatusForceThrow(env, status);
   return (jint)analog;
 }
 
@@ -57,10 +60,10 @@ Java_edu_wpi_first_hal_AnalogJNI_initializeAnalogOutputPort
   (JNIEnv* env, jclass, jint id)
 {
   int32_t status = 0;
-  HAL_AnalogOutputHandle analog =
-      HAL_InitializeAnalogOutputPort((HAL_PortHandle)id, &status);
-  CheckStatusRange(env, status, 0, HAL_GetNumAnalogOutputs(),
-                   hal::getPortHandleChannel((HAL_PortHandle)id));
+  auto stack = wpi::java::GetJavaStackTrace(env, "edu.wpi.first");
+  HAL_AnalogOutputHandle analog = HAL_InitializeAnalogOutputPort(
+      (HAL_PortHandle)id, stack.c_str(), &status);
+  CheckStatusForceThrow(env, status);
   return (jlong)analog;
 }
 

hal/src/main/native/cpp/jni/CounterJNI.cpp

@@ -119,12 +119,6 @@ Java_edu_wpi_first_hal_CounterJNI_setCounterDownSource
   HAL_SetCounterDownSource((HAL_CounterHandle)id,
                            (HAL_Handle)digitalSourceHandle,
                            (HAL_AnalogTriggerType)analogTriggerType, &status);
-  if (status == PARAMETER_OUT_OF_RANGE) {
-    ThrowIllegalArgumentException(env,
-                                  "Counter only supports DownSource in "
-                                  "TwoPulse and ExternalDirection modes.");
-    return;
-  }
   CheckStatus(env, status);
 }
 
@@ -240,10 +234,6 @@ Java_edu_wpi_first_hal_CounterJNI_setCounterSamplesToAverage
 {
   int32_t status = 0;
   HAL_SetCounterSamplesToAverage((HAL_CounterHandle)id, value, &status);
-  if (status == PARAMETER_OUT_OF_RANGE) {
-    ThrowBoundaryException(env, value, 1, 127);
-    return;
-  }
   CheckStatus(env, status);
 }
 

hal/src/main/native/cpp/jni/DIOJNI.cpp

@@ -6,6 +6,8 @@
 
 #include <cassert>
 
+#include <wpi/jni_util.h>
+
 #include "HALUtil.h"
 #include "edu_wpi_first_hal_DIOJNI.h"
 #include "hal/DIO.h"
@@ -27,10 +29,10 @@ Java_edu_wpi_first_hal_DIOJNI_initializeDIOPort
   (JNIEnv* env, jclass, jint id, jboolean input)
 {
   int32_t status = 0;
-  auto dio = HAL_InitializeDIOPort((HAL_PortHandle)id,
-                                   static_cast<uint8_t>(input), &status);
-  CheckStatusRange(env, status, 0, HAL_GetNumDigitalChannels(),
-                   hal::getPortHandleChannel((HAL_PortHandle)id));
+  auto stack = wpi::java::GetJavaStackTrace(env, "edu.wpi.first");
+  auto dio = HAL_InitializeDIOPort(
+      (HAL_PortHandle)id, static_cast<uint8_t>(input), stack.c_str(), &status);
+  CheckStatusForceThrow(env, status);
   return (jint)dio;
 }
 

hal/src/main/native/cpp/jni/EncoderJNI.cpp

@@ -267,10 +267,6 @@ Java_edu_wpi_first_hal_EncoderJNI_setEncoderSamplesToAverage
 {
   int32_t status = 0;
   HAL_SetEncoderSamplesToAverage((HAL_EncoderHandle)id, value, &status);
-  if (status == PARAMETER_OUT_OF_RANGE) {
-    ThrowBoundaryException(env, value, 1, 127);
-    return;
-  }
   CheckStatus(env, status);
 }
 

hal/src/main/native/cpp/jni/HALUtil.cpp

@@ -83,20 +83,18 @@ void ThrowUncleanStatusException(JNIEnv* env, wpi::StringRef msg,
   env->Throw(static_cast<jthrowable>(exception));
 }
 
-void ThrowAllocationException(JNIEnv* env, int32_t minRange, int32_t maxRange,
-                              int32_t requestedValue, int32_t status) {
-  const char* message = HAL_GetErrorMessage(status);
+void ThrowAllocationException(JNIEnv* env, const char* lastError,
+                              int32_t status) {
   wpi::SmallString<1024> buf;
   wpi::raw_svector_ostream oss(buf);
-  oss << " Code: " << status << ". " << message
-      << ", Minimum Value: " << minRange << ", Maximum Value: " << maxRange
-      << ", Requested Value: " << requestedValue;
-  env->ThrowNew(allocationExCls, buf.c_str());
+
+  oss << "Code: " << status << '\n' << lastError;
+
   allocationExCls.Throw(env, buf.c_str());
 }
 
 void ThrowHalHandleException(JNIEnv* env, int32_t status) {
-  const char* message = HAL_GetErrorMessage(status);
+  const char* message = HAL_GetLastError(&status);
   wpi::SmallString<1024> buf;
   wpi::raw_svector_ostream oss(buf);
   oss << " Code: " << status << ". " << message;
@@ -107,10 +105,11 @@ void ReportError(JNIEnv* env, int32_t status, bool doThrow) {
   if (status == 0) {
     return;
   }
+  const char* message = HAL_GetLastError(&status);
   if (status == HAL_HANDLE_ERROR) {
     ThrowHalHandleException(env, status);
+    return;
   }
-  const char* message = HAL_GetErrorMessage(status);
   if (doThrow && status < 0) {
     wpi::SmallString<1024> buf;
     wpi::raw_svector_ostream oss(buf);
@@ -119,7 +118,11 @@ void ReportError(JNIEnv* env, int32_t status, bool doThrow) {
   } else {
     std::string func;
     auto stack = GetJavaStackTrace(env, &func, "edu.wpi.first");
-    HAL_SendError(1, status, 0, message, func.c_str(), stack.c_str(), 1);
+    // Make a copy of message for safety, calling back into the HAL might
+    // invalidate the string.
+    wpi::SmallString<256> lastMessage{wpi::StringRef{message}};
+    HAL_SendError(1, status, 0, lastMessage.c_str(), func.c_str(),
+                  stack.c_str(), 1);
   }
 }
 
@@ -128,17 +131,19 @@ void ThrowError(JNIEnv* env, int32_t status, int32_t minRange, int32_t maxRange,
   if (status == 0) {
     return;
   }
+  const char* lastError = HAL_GetLastError(&status);
   if (status == NO_AVAILABLE_RESOURCES || status == RESOURCE_IS_ALLOCATED ||
       status == RESOURCE_OUT_OF_RANGE) {
-    ThrowAllocationException(env, minRange, maxRange, requestedValue, status);
+    ThrowAllocationException(env, lastError, status);
+    return;
   }
   if (status == HAL_HANDLE_ERROR) {
     ThrowHalHandleException(env, status);
+    return;
   }
-  const char* message = HAL_GetErrorMessage(status);
   wpi::SmallString<1024> buf;
   wpi::raw_svector_ostream oss(buf);
-  oss << " Code: " << status << ". " << message;
+  oss << " Code: " << status << ". " << lastError;
   ThrowUncleanStatusException(env, buf.c_str(), status);
 }
 

hal/src/main/native/cpp/jni/PWMJNI.cpp

@@ -6,6 +6,8 @@
 
 #include <cassert>
 
+#include <wpi/jni_util.h>
+
 #include "HALUtil.h"
 #include "edu_wpi_first_hal_PWMJNI.h"
 #include "hal/DIO.h"
@@ -27,9 +29,9 @@ Java_edu_wpi_first_hal_PWMJNI_initializePWMPort
   (JNIEnv* env, jclass, jint id)
 {
   int32_t status = 0;
-  auto pwm = HAL_InitializePWMPort((HAL_PortHandle)id, &status);
-  CheckStatusRange(env, status, 0, HAL_GetNumPWMChannels(),
-                   hal::getPortHandleChannel((HAL_PortHandle)id));
+  auto stack = wpi::java::GetJavaStackTrace(env, "edu.wpi.first");
+  auto pwm = HAL_InitializePWMPort((HAL_PortHandle)id, stack.c_str(), &status);
+  CheckStatusForceThrow(env, status);
   return (jint)pwm;
 }
 

hal/src/main/native/cpp/jni/RelayJNI.cpp

@@ -6,6 +6,8 @@
 
 #include <cassert>
 
+#include <wpi/jni_util.h>
+
 #include "HALUtil.h"
 #include "edu_wpi_first_hal_RelayJNI.h"
 #include "hal/Ports.h"
@@ -26,10 +28,10 @@ Java_edu_wpi_first_hal_RelayJNI_initializeRelayPort
   (JNIEnv* env, jclass, jint id, jboolean fwd)
 {
   int32_t status = 0;
+  auto stack = wpi::java::GetJavaStackTrace(env, "edu.wpi.first");
   HAL_RelayHandle handle = HAL_InitializeRelayPort(
-      (HAL_PortHandle)id, static_cast<uint8_t>(fwd), &status);
-  CheckStatusRange(env, status, 0, HAL_GetNumRelayChannels(),
-                   hal::getPortHandleChannel((HAL_PortHandle)id));
+      (HAL_PortHandle)id, static_cast<uint8_t>(fwd), stack.c_str(), &status);
+  CheckStatusForceThrow(env, status);
   return (jint)handle;
 }
 

hal/src/main/native/cpp/jni/simulation/SimDeviceDataJNI.cpp

@@ -109,8 +109,6 @@ class DeviceCallbackStore {
 
 class ValueCallbackStore {
  public:
-  explicit ValueCallbackStore(bool dirCallback) : m_dirCallback{dirCallback} {}
-
   void create(JNIEnv* env, jobject obj) { m_call = JGlobal<jobject>(env, obj); }
   void performCallback(const char* name, HAL_SimValueHandle handle,
                        int32_t direction, const HAL_Value& value);
@@ -121,7 +119,6 @@ class ValueCallbackStore {
  private:
   wpi::java::JGlobal<jobject> m_call;
   int32_t m_callbackId;
-  bool m_dirCallback;
 };
 
 }  // namespace
@@ -181,17 +178,9 @@ void ValueCallbackStore::performCallback(const char* name,
   }
 
   auto [value1, value2] = ToValue12(value);
-  if (m_dirCallback) {
-    env->CallVoidMethod(m_call, simValueCallbackCallback,
-                        MakeJString(env, name), static_cast<jint>(handle),
-                        static_cast<jint>(direction),
-                        static_cast<jint>(value.type), value1, value2);
-  } else {
-    env->CallVoidMethod(m_call, simValueCallbackCallback,
-                        MakeJString(env, name), static_cast<jint>(handle),
-                        static_cast<jboolean>(direction == HAL_SimValueOutput),
-                        static_cast<jint>(value.type), value1, value2);
-  }
+  env->CallVoidMethod(m_call, simValueCallbackCallback, MakeJString(env, name),
+                      static_cast<jint>(handle), static_cast<jint>(direction),
+                      static_cast<jint>(value.type), value1, value2);
 
   if (env->ExceptionCheck()) {
     env->ExceptionDescribe();
@@ -266,12 +255,11 @@ using FreeValueCallbackFunc = void (*)(int32_t uid);
 
 template <typename THandle>
 static SIM_JniHandle AllocateValueCallback(
-    JNIEnv* env, THandle h, jobject callback, bool dirCallback,
-    jboolean initialNotify,
+    JNIEnv* env, THandle h, jobject callback, jboolean initialNotify,
     int32_t (*createCallback)(THandle handle, void* param,
                               HALSIM_SimValueCallback callback,
                               HAL_Bool initialNotify)) {
-  auto callbackStore = std::make_shared<ValueCallbackStore>(dirCallback);
+  auto callbackStore = std::make_shared<ValueCallbackStore>();
 
   auto handle = valueCallbackHandles->Allocate(callbackStore);
 
@@ -345,7 +333,7 @@ bool InitializeSimDeviceDataJNI(JNIEnv* env) {
   }
 
   simValueCallbackCallback = env->GetMethodID(
-      simValueCallbackCls, "callbackNative", "(Ljava/lang/String;IZIJD)V");
+      simValueCallbackCls, "callbackNative", "(Ljava/lang/String;IIIJD)V");
   if (!simValueCallbackCallback) {
     return false;
   }
@@ -530,21 +518,7 @@ Java_edu_wpi_first_hal_simulation_SimDeviceDataJNI_registerSimValueCreatedCallba
   (JNIEnv* env, jclass, jint device, jobject callback, jboolean initialNotify)
 {
   return AllocateValueCallback(env, static_cast<HAL_SimDeviceHandle>(device),
-                               callback, false, initialNotify,
-                               &HALSIM_RegisterSimValueCreatedCallback);
-}
-
-/*
- * Class:     edu_wpi_first_hal_simulation_SimDeviceDataJNI
- * Method:    registerSimValueCreatedCallback2
- * Signature: (ILjava/lang/Object;Z)I
- */
-JNIEXPORT jint JNICALL
-Java_edu_wpi_first_hal_simulation_SimDeviceDataJNI_registerSimValueCreatedCallback2
-  (JNIEnv* env, jclass, jint device, jobject callback, jboolean initialNotify)
-{
-  return AllocateValueCallback(env, static_cast<HAL_SimDeviceHandle>(device),
-                               callback, true, initialNotify,
+                               callback, initialNotify,
                                &HALSIM_RegisterSimValueCreatedCallback);
 }
 
@@ -570,21 +544,7 @@ Java_edu_wpi_first_hal_simulation_SimDeviceDataJNI_registerSimValueChangedCallba
   (JNIEnv* env, jclass, jint handle, jobject callback, jboolean initialNotify)
 {
   return AllocateValueCallback(env, static_cast<HAL_SimValueHandle>(handle),
-                               callback, false, initialNotify,
-                               &HALSIM_RegisterSimValueChangedCallback);
-}
-
-/*
- * Class:     edu_wpi_first_hal_simulation_SimDeviceDataJNI
- * Method:    registerSimValueChangedCallback2
- * Signature: (ILjava/lang/Object;Z)I
- */
-JNIEXPORT jint JNICALL
-Java_edu_wpi_first_hal_simulation_SimDeviceDataJNI_registerSimValueChangedCallback2
-  (JNIEnv* env, jclass, jint handle, jobject callback, jboolean initialNotify)
-{
-  return AllocateValueCallback(env, static_cast<HAL_SimValueHandle>(handle),
-                               callback, true, initialNotify,
+                               callback, initialNotify,
                                &HALSIM_RegisterSimValueChangedCallback);
 }
 
@@ -610,7 +570,7 @@ Java_edu_wpi_first_hal_simulation_SimDeviceDataJNI_registerSimValueResetCallback
   (JNIEnv* env, jclass, jint handle, jobject callback, jboolean initialNotify)
 {
   return AllocateValueCallback(env, static_cast<HAL_SimValueHandle>(handle),
-                               callback, true, initialNotify,
+                               callback, initialNotify,
                                &HALSIM_RegisterSimValueResetCallback);
 }
 

hal/src/main/native/include/hal/AnalogGyro.h

@@ -22,9 +22,12 @@ extern "C" {
  * Initializes an analog gyro.
  *
  * @param handle handle to the analog port
+ * @param allocationLocation    the location where the allocation is occuring
+ * (can be null)
  * @return       the initialized gyro handle
  */
 HAL_GyroHandle HAL_InitializeAnalogGyro(HAL_AnalogInputHandle handle,
+                                        const char* allocationLocation,
                                         int32_t* status);
 
 /**

hal/src/main/native/include/hal/AnalogInput.h

@@ -22,10 +22,12 @@ extern "C" {
  * Initializes the analog input port using the given port object.
  *
  * @param portHandle Handle to the port to initialize.
+ * @param allocationLocation    the location where the allocation is occuring
+ * (can be null)
  * @return           the created analog input handle
  */
-HAL_AnalogInputHandle HAL_InitializeAnalogInputPort(HAL_PortHandle portHandle,
-                                                    int32_t* status);
+HAL_AnalogInputHandle HAL_InitializeAnalogInputPort(
+    HAL_PortHandle portHandle, const char* allocationLocation, int32_t* status);
 
 /**
  * Frees an analog input port.

hal/src/main/native/include/hal/AnalogOutput.h

@@ -22,10 +22,12 @@ extern "C" {
  * Initializes the analog output port using the given port object.
  *
  * @param handle handle to the port
+ * @param allocationLocation    the location where the allocation is occuring
+ * (can be null)
  * @return       the created analog output handle
  */
-HAL_AnalogOutputHandle HAL_InitializeAnalogOutputPort(HAL_PortHandle portHandle,
-                                                      int32_t* status);
+HAL_AnalogOutputHandle HAL_InitializeAnalogOutputPort(
+    HAL_PortHandle portHandle, const char* allocationLocation, int32_t* status);
 
 /**
  * Frees an analog output port.

hal/src/main/native/include/hal/DIO.h

@@ -21,12 +21,16 @@ extern "C" {
 /**
  * Creates a new instance of a digital port.
  *
- * @param portHandle the port handle to create from
- * @param input      true for input, false for output
- * @return           the created digital handle
+ * @param portHandle            the port handle to create from
+ * @param input                 true for input, false for output
+ * @param allocationLocation    the location where the allocation is occuring
+ * (can be null)
+ * @return                      the created digital handle
  */
 HAL_DigitalHandle HAL_InitializeDIOPort(HAL_PortHandle portHandle,
-                                        HAL_Bool input, int32_t* status);
+                                        HAL_Bool input,
+                                        const char* allocationLocation,
+                                        int32_t* status);
 
 /**
  * Checks if a DIO channel is valid.

hal/src/main/native/include/hal/Errors.h

@@ -41,6 +41,8 @@
 #define ERR_FRCSystem_NoDSConnection_MESSAGE \
   "FRCSystem: No driver station connected"
 
+#define HAL_SUCCESS 0
+
 #define SAMPLE_RATE_TOO_HIGH 1001
 #define SAMPLE_RATE_TOO_HIGH_MESSAGE \
   "HAL: Analog module sample rate is too high"
@@ -125,6 +127,10 @@
 #define HAL_SIM_NOT_SUPPORTED -1155
 #define HAL_SIM_NOT_SUPPORTED_MESSAGE "HAL: Method not supported in sim"
 
+#define HAL_USE_LAST_ERROR -1156
+#define HAL_USE_LAST_ERROR_MESSAGE \
+  "HAL: Use HAL_GetLastError(status) to get last error"
+
 #define HAL_CAN_BUFFER_OVERRUN -35007
 #define HAL_CAN_BUFFER_OVERRUN_MESSAGE \
   "HAL: CAN Output Buffer Full. Ensure a device is attached"

hal/src/main/native/include/hal/HALBase.h

@@ -22,6 +22,19 @@ HAL_ENUM(HAL_RuntimeType) { HAL_Athena, HAL_Mock };
 extern "C" {
 #endif
 
+/**
+ * Gets the last error set on this thread, or the message for the status code.
+ *
+ * If passed HAL_USE_LAST_ERROR, the last error set on the thread will be
+ * returned.
+ *
+ * @param code  the status code, set to the error status code if input is
+ * HAL_USE_LAST_ERROR
+ * @return      the error message for the code. This does not need to be freed,
+ * but can be overwritten by another hal call on the same thread.
+ */
+const char* HAL_GetLastError(int32_t* status);
+
 /**
  * Gets the error message for a specific status code.
  *

hal/src/main/native/include/hal/PWM.h

@@ -22,9 +22,12 @@ extern "C" {
  * Initializes a PWM port.
  *
  * @param portHandle the port to initialize
+ * @param allocationLocation    the location where the allocation is occuring
+ * (can be null)
  * @return           the created pwm handle
  */
 HAL_DigitalHandle HAL_InitializePWMPort(HAL_PortHandle portHandle,
+                                        const char* allocationLocation,
                                         int32_t* status);
 
 /**

hal/src/main/native/include/hal/Relay.h

@@ -26,9 +26,12 @@ extern "C" {
  *
  * @param portHandle the port handle to initialize
  * @param fwd        true for the forward port, false for the reverse port
+ * @param allocationLocation    the location where the allocation is occuring
+ * (can be null)
  * @return           the created relay handle
  */
 HAL_RelayHandle HAL_InitializeRelayPort(HAL_PortHandle portHandle, HAL_Bool fwd,
+                                        const char* allocationLocation,
                                         int32_t* status);
 
 /**

hal/src/main/native/include/hal/handles/DigitalHandleResource.h

@@ -22,7 +22,7 @@ namespace hal {
  * allows a limited number of handles that are allocated by index.
  * The enum value is separate, as 2 enum values are allowed per handle
  * Because they are allocated by index, each individual index holds its own
- * mutex, which reduces contention heavily.]
+ * mutex, which reduces contention heavily.
  *
  * @tparam THandle The Handle Type (Must be typedefed from HAL_Handle)
  * @tparam TStruct The struct type held by this resource
@@ -38,7 +38,8 @@ class DigitalHandleResource : public HandleBase {
   DigitalHandleResource(const DigitalHandleResource&) = delete;
   DigitalHandleResource& operator=(const DigitalHandleResource&) = delete;
 
-  THandle Allocate(int16_t index, HAL_HandleEnum enumValue, int32_t* status);
+  std::shared_ptr<TStruct> Allocate(int16_t index, HAL_HandleEnum enumValue,
+                                    THandle* handle, int32_t* status);
   int16_t GetIndex(THandle handle, HAL_HandleEnum enumValue) {
     return getHandleTypedIndex(handle, enumValue, m_version);
   }
@@ -52,21 +53,27 @@ class DigitalHandleResource : public HandleBase {
 };
 
 template <typename THandle, typename TStruct, int16_t size>
-THandle DigitalHandleResource<THandle, TStruct, size>::Allocate(
-    int16_t index, HAL_HandleEnum enumValue, int32_t* status) {
+std::shared_ptr<TStruct>
+DigitalHandleResource<THandle, TStruct, size>::Allocate(
+    int16_t index, HAL_HandleEnum enumValue, THandle* handle, int32_t* status) {
   // don't acquire the lock if we can fail early.
   if (index < 0 || index >= size) {
+    *handle = HAL_kInvalidHandle;
     *status = RESOURCE_OUT_OF_RANGE;
-    return HAL_kInvalidHandle;
+    return nullptr;
   }
   std::scoped_lock lock(m_handleMutexes[index]);
   // check for allocation, otherwise allocate and return a valid handle
   if (m_structures[index] != nullptr) {
+    *handle = HAL_kInvalidHandle;
     *status = RESOURCE_IS_ALLOCATED;
-    return HAL_kInvalidHandle;
+    return m_structures[index];
   }
   m_structures[index] = std::make_shared<TStruct>();
-  return static_cast<THandle>(hal::createHandle(index, enumValue, m_version));
+  *handle =
+      static_cast<THandle>(hal::createHandle(index, enumValue, m_version));
+  *status = HAL_SUCCESS;
+  return m_structures[index];
 }
 
 template <typename THandle, typename TStruct, int16_t size>

hal/src/main/native/include/hal/handles/IndexedHandleResource.h

@@ -39,7 +39,8 @@ class IndexedHandleResource : public HandleBase {
   IndexedHandleResource(const IndexedHandleResource&) = delete;
   IndexedHandleResource& operator=(const IndexedHandleResource&) = delete;
 
-  THandle Allocate(int16_t index, int32_t* status);
+  std::shared_ptr<TStruct> Allocate(int16_t index, THandle* handle,
+                                    int32_t* status);
   int16_t GetIndex(THandle handle) {
     return getHandleTypedIndex(handle, enumValue, m_version);
   }
@@ -54,21 +55,27 @@ class IndexedHandleResource : public HandleBase {
 
 template <typename THandle, typename TStruct, int16_t size,
           HAL_HandleEnum enumValue>
-THandle IndexedHandleResource<THandle, TStruct, size, enumValue>::Allocate(
-    int16_t index, int32_t* status) {
+std::shared_ptr<TStruct>
+IndexedHandleResource<THandle, TStruct, size, enumValue>::Allocate(
+    int16_t index, THandle* handle, int32_t* status) {
   // don't acquire the lock if we can fail early.
   if (index < 0 || index >= size) {
     *status = RESOURCE_OUT_OF_RANGE;
-    return HAL_kInvalidHandle;
+    *handle = HAL_kInvalidHandle;
+    return nullptr;
   }
   std::scoped_lock lock(m_handleMutexes[index]);
   // check for allocation, otherwise allocate and return a valid handle
   if (m_structures[index] != nullptr) {
     *status = RESOURCE_IS_ALLOCATED;
-    return HAL_kInvalidHandle;
+    *handle = HAL_kInvalidHandle;
+    return m_structures[index];
   }
   m_structures[index] = std::make_shared<TStruct>();
-  return static_cast<THandle>(hal::createHandle(index, enumValue, m_version));
+  *handle =
+      static_cast<THandle>(hal::createHandle(index, enumValue, m_version));
+  *status = HAL_SUCCESS;
+  return m_structures[index];
 }
 
 template <typename THandle, typename TStruct, int16_t size,

hal/src/main/native/sim/AddressableLED.cpp

@@ -6,6 +6,7 @@
 
 #include "DigitalInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/Errors.h"
 #include "hal/handles/HandlesInternal.h"
@@ -110,8 +111,11 @@ void HAL_SetAddressableLEDLength(HAL_AddressableLEDHandle handle,
     *status = HAL_HANDLE_ERROR;
     return;
   }
-  if (length > HAL_kAddressableLEDMaxLength) {
+  if (length > HAL_kAddressableLEDMaxLength || length < 0) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status, "LED length must be less than or equal to " +
+                                  wpi::Twine(HAL_kAddressableLEDMaxLength) +
+                                  ". " + wpi::Twine(length) + " was requested");
     return;
   }
   SimAddressableLEDData[led->index].length = length;
@@ -127,6 +131,10 @@ void HAL_WriteAddressableLEDData(HAL_AddressableLEDHandle handle,
   }
   if (length > SimAddressableLEDData[led->index].length) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status,
+                      "Data length must be less than or equal to " +
+                          wpi::Twine(SimAddressableLEDData[led->index].length) +
+                          ". " + wpi::Twine(length) + " was requested");
     return;
   }
   SimAddressableLEDData[led->index].SetData(data, length);

hal/src/main/native/sim/AnalogGyro.cpp

@@ -4,7 +4,10 @@
 
 #include "hal/AnalogGyro.h"
 
+#include <string>
+
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/AnalogAccumulator.h"
 #include "hal/Errors.h"
@@ -15,6 +18,7 @@ namespace {
 struct AnalogGyro {
   HAL_AnalogInputHandle handle;
   uint8_t index;
+  std::string previousAllocation;
 };
 }  // namespace
 
@@ -34,36 +38,41 @@ void InitializeAnalogGyro() {
 
 extern "C" {
 HAL_GyroHandle HAL_InitializeAnalogGyro(HAL_AnalogInputHandle analogHandle,
+                                        const char* allocationLocation,
                                         int32_t* status) {
   hal::init::CheckInit();
+  // Handle will be type checked by HAL_IsAccumulatorChannel
+  int16_t channel = getHandleIndex(analogHandle);
   if (!HAL_IsAccumulatorChannel(analogHandle, status)) {
     if (*status == 0) {
       *status = HAL_INVALID_ACCUMULATOR_CHANNEL;
+      hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for Analog Gyro",
+                                       0, kNumAccumulators, channel);
     }
     return HAL_kInvalidHandle;
   }
 
-  // handle known to be correct, so no need to type check
-  int16_t channel = getHandleIndex(analogHandle);
-
-  auto handle = analogGyroHandles->Allocate(channel, status);
+  HAL_GyroHandle handle;
+  auto gyro = analogGyroHandles->Allocate(channel, &handle, status);
 
   if (*status != 0) {
+    if (gyro) {
+      hal::SetLastErrorPreviouslyAllocated(status, "Analog Gyro", channel,
+                                           gyro->previousAllocation);
+    } else {
+      hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for Analog Gyro",
+                                       0, kNumAccumulators, channel);
+    }
     return HAL_kInvalidHandle;  // failed to allocate. Pass error back.
   }
 
-  // Initialize port structure
-  auto gyro = analogGyroHandles->Get(handle);
-  if (gyro == nullptr) {  // would only error on thread issue
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
-
   gyro->handle = analogHandle;
   gyro->index = channel;
 
   SimAnalogGyroData[channel].initialized = true;
 
+  gyro->previousAllocation = allocationLocation ? allocationLocation : "";
+
   return handle;
 }
 

hal/src/main/native/sim/AnalogInput.cpp

@@ -6,6 +6,7 @@
 
 #include "AnalogInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/AnalogAccumulator.h"
 #include "hal/handles/HandlesInternal.h"
@@ -18,28 +19,32 @@ void InitializeAnalogInput() {}
 }  // namespace hal::init
 
 extern "C" {
-HAL_AnalogInputHandle HAL_InitializeAnalogInputPort(HAL_PortHandle portHandle,
-                                                    int32_t* status) {
+HAL_AnalogInputHandle HAL_InitializeAnalogInputPort(
+    HAL_PortHandle portHandle, const char* allocationLocation,
+    int32_t* status) {
   hal::init::CheckInit();
   int16_t channel = getPortHandleChannel(portHandle);
-  if (channel == InvalidHandleIndex) {
-    *status = PARAMETER_OUT_OF_RANGE;
+  if (channel == InvalidHandleIndex || channel >= kNumAnalogInputs) {
+    *status = RESOURCE_OUT_OF_RANGE;
+    hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for Analog Input",
+                                     0, kNumAnalogInputs, channel);
     return HAL_kInvalidHandle;
   }
 
-  HAL_AnalogInputHandle handle = analogInputHandles->Allocate(channel, status);
+  HAL_AnalogInputHandle handle;
+  auto analog_port = analogInputHandles->Allocate(channel, &handle, status);
 
   if (*status != 0) {
+    if (analog_port) {
+      hal::SetLastErrorPreviouslyAllocated(status, "Analog Input", channel,
+                                           analog_port->previousAllocation);
+    } else {
+      hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for Analog Input",
+                                       0, kNumAnalogInputs, channel);
+    }
     return HAL_kInvalidHandle;  // failed to allocate. Pass error back.
   }
 
-  // Initialize port structure
-  auto analog_port = analogInputHandles->Get(handle);
-  if (analog_port == nullptr) {  // would only error on thread issue
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
-
   analog_port->channel = static_cast<uint8_t>(channel);
   if (HAL_IsAccumulatorChannel(handle, status)) {
     analog_port->isAccumulator = true;
@@ -51,6 +56,9 @@ HAL_AnalogInputHandle HAL_InitializeAnalogInputPort(HAL_PortHandle portHandle,
   SimAnalogInData[channel].accumulatorInitialized = false;
   SimAnalogInData[channel].simDevice = 0;
 
+  analog_port->previousAllocation =
+      allocationLocation ? allocationLocation : "";
+
   return handle;
 }
 void HAL_FreeAnalogInputPort(HAL_AnalogInputHandle analogPortHandle) {

hal/src/main/native/sim/AnalogInternal.h

@@ -6,6 +6,8 @@
 
 #include <stdint.h>
 
+#include <string>
+
 #include "PortsInternal.h"
 #include "hal/handles/HandlesInternal.h"
 #include "hal/handles/IndexedHandleResource.h"
@@ -20,6 +22,7 @@ static constexpr uint32_t kAccumulatorChannels[] = {0, 1};
 struct AnalogPort {
   uint8_t channel;
   bool isAccumulator;
+  std::string previousAllocation;
 };
 
 extern IndexedHandleResource<HAL_AnalogInputHandle, hal::AnalogPort,

hal/src/main/native/sim/AnalogOutput.cpp

@@ -4,7 +4,10 @@
 
 #include "hal/AnalogOutput.h"
 
+#include <string>
+
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/Errors.h"
 #include "hal/handles/HandlesInternal.h"
@@ -16,6 +19,7 @@ using namespace hal;
 namespace {
 struct AnalogOutput {
   uint8_t channel;
+  std::string previousAllocation;
 };
 }  // namespace
 
@@ -33,32 +37,39 @@ void InitializeAnalogOutput() {
 }  // namespace hal::init
 
 extern "C" {
-HAL_AnalogOutputHandle HAL_InitializeAnalogOutputPort(HAL_PortHandle portHandle,
-                                                      int32_t* status) {
+HAL_AnalogOutputHandle HAL_InitializeAnalogOutputPort(
+    HAL_PortHandle portHandle, const char* allocationLocation,
+    int32_t* status) {
   hal::init::CheckInit();
   int16_t channel = getPortHandleChannel(portHandle);
-  if (channel == InvalidHandleIndex) {
-    *status = PARAMETER_OUT_OF_RANGE;
+  if (channel == InvalidHandleIndex || channel >= kNumAnalogOutputs) {
+    *status = RESOURCE_OUT_OF_RANGE;
+    hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for Analog Output",
+                                     0, kNumAnalogOutputs, channel);
     return HAL_kInvalidHandle;
   }
 
-  HAL_AnalogOutputHandle handle =
-      analogOutputHandles->Allocate(channel, status);
+  HAL_AnalogOutputHandle handle;
+  auto port = analogOutputHandles->Allocate(channel, &handle, status);
 
   if (*status != 0) {
+    if (port) {
+      hal::SetLastErrorPreviouslyAllocated(status, "Analog Output", channel,
+                                           port->previousAllocation);
+    } else {
+      hal::SetLastErrorIndexOutOfRange(status,
+                                       "Invalid Index for Analog Output", 0,
+                                       kNumAnalogOutputs, channel);
+    }
     return HAL_kInvalidHandle;  // failed to allocate. Pass error back.
   }
 
-  auto port = analogOutputHandles->Get(handle);
-  if (port == nullptr) {  // would only error on thread issue
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
-
   port->channel = static_cast<uint8_t>(channel);
 
   // Initialize sim analog input
   SimAnalogOutData[channel].initialized = true;
+
+  port->previousAllocation = allocationLocation ? allocationLocation : "";
   return handle;
 }
 

hal/src/main/native/sim/DIO.cpp

@@ -6,6 +6,7 @@
 
 #include "DigitalInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/handles/HandlesInternal.h"
 #include "hal/handles/LimitedHandleResource.h"
@@ -31,36 +32,41 @@ void InitializeDIO() {
 extern "C" {
 
 HAL_DigitalHandle HAL_InitializeDIOPort(HAL_PortHandle portHandle,
-                                        HAL_Bool input, int32_t* status) {
+                                        HAL_Bool input,
+                                        const char* allocationLocation,
+                                        int32_t* status) {
   hal::init::CheckInit();
-  if (*status != 0) {
-    return HAL_kInvalidHandle;
-  }
 
   int16_t channel = getPortHandleChannel(portHandle);
   if (channel == InvalidHandleIndex) {
-    *status = PARAMETER_OUT_OF_RANGE;
+    *status = RESOURCE_OUT_OF_RANGE;
+    hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for DIO", 0,
+                                     kNumDigitalChannels, channel);
     return HAL_kInvalidHandle;
   }
 
-  auto handle =
-      digitalChannelHandles->Allocate(channel, HAL_HandleEnum::DIO, status);
+  HAL_DigitalHandle handle;
+
+  auto port = digitalChannelHandles->Allocate(channel, HAL_HandleEnum::DIO,
+                                              &handle, status);
 
   if (*status != 0) {
+    if (port) {
+      hal::SetLastErrorPreviouslyAllocated(status, "PWM or DIO", channel,
+                                           port->previousAllocation);
+    } else {
+      hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for DIO", 0,
+                                       kNumDigitalChannels, channel);
+    }
     return HAL_kInvalidHandle;  // failed to allocate. Pass error back.
   }
 
-  auto port = digitalChannelHandles->Get(handle, HAL_HandleEnum::DIO);
-  if (port == nullptr) {  // would only occur on thread issue.
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
-
   port->channel = static_cast<uint8_t>(channel);
 
   SimDIOData[channel].initialized = true;
   SimDIOData[channel].isInput = input;
   SimDIOData[channel].simDevice = 0;
+  port->previousAllocation = allocationLocation ? allocationLocation : "";
 
   return handle;
 }

hal/src/main/native/sim/DigitalInternal.h

@@ -6,6 +6,8 @@
 
 #include <stdint.h>
 
+#include <string>
+
 #include "PortsInternal.h"
 #include "hal/AnalogTrigger.h"
 #include "hal/handles/DigitalHandleResource.h"
@@ -56,6 +58,7 @@ struct DigitalPort {
   int32_t centerPwm = 0;
   int32_t deadbandMinPwm = 0;
   int32_t minPwm = 0;
+  std::string previousAllocation;
 };
 
 extern DigitalHandleResource<HAL_DigitalHandle, DigitalPort,

hal/src/main/native/sim/Encoder.cpp

@@ -6,6 +6,7 @@
 
 #include "CounterInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/Errors.h"
 #include "hal/handles/HandlesInternal.h"
@@ -246,6 +247,7 @@ void HAL_SetEncoderMinRate(HAL_EncoderHandle encoderHandle, double minRate,
 
   if (minRate == 0.0) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status, "minRate must not be 0");
     return;
   }
 
@@ -262,6 +264,7 @@ void HAL_SetEncoderDistancePerPulse(HAL_EncoderHandle encoderHandle,
 
   if (distancePerPulse == 0.0) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status, "distancePerPulse must not be 0");
     return;
   }
   encoder->distancePerPulse = distancePerPulse;

hal/src/main/native/sim/HAL.cpp

@@ -250,6 +250,8 @@ const char* HAL_GetErrorMessage(int32_t code) {
       return HAL_CAN_BUFFER_OVERRUN_MESSAGE;
     case HAL_LED_CHANNEL_ERROR:
       return HAL_LED_CHANNEL_ERROR_MESSAGE;
+    case HAL_USE_LAST_ERROR:
+      return HAL_USE_LAST_ERROR_MESSAGE;
     default:
       return "Unknown error status";
   }

hal/src/main/native/sim/HALInternal.h

@@ -0,0 +1,19 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+#include <stdint.h>
+
+#include <wpi/Twine.h>
+
+namespace hal {
+void SetLastError(int32_t* status, const wpi::Twine& value);
+void SetLastErrorIndexOutOfRange(int32_t* status, const wpi::Twine& message,
+                                 int32_t minimum, int32_t maximum,
+                                 int32_t channel);
+void SetLastErrorPreviouslyAllocated(int32_t* status, const wpi::Twine& message,
+                                     int32_t channel,
+                                     const wpi::Twine& previousAllocation);
+}  // namespace hal

hal/src/main/native/sim/PDP.cpp

@@ -6,6 +6,7 @@
 
 #include "CANAPIInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/CANAPI.h"
 #include "hal/Errors.h"
@@ -27,6 +28,7 @@ extern "C" {
 HAL_PDPHandle HAL_InitializePDP(int32_t module, int32_t* status) {
   if (!HAL_CheckPDPModule(module)) {
     *status = PARAMETER_OUT_OF_RANGE;
+    hal::SetLastError(status, "Invalid pdp module " + wpi::Twine(module));
     return HAL_kInvalidHandle;
   }
   hal::init::CheckInit();

hal/src/main/native/sim/PWM.cpp

@@ -7,6 +7,7 @@
 #include "ConstantsInternal.h"
 #include "DigitalInternal.h"
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/handles/HandlesInternal.h"
 #include "mockdata/PWMDataInternal.h"
@@ -20,15 +21,15 @@ void InitializePWM() {}
 extern "C" {
 
 HAL_DigitalHandle HAL_InitializePWMPort(HAL_PortHandle portHandle,
+                                        const char* allocationLocation,
                                         int32_t* status) {
   hal::init::CheckInit();
-  if (*status != 0) {
-    return HAL_kInvalidHandle;
-  }
 
   int16_t channel = getPortHandleChannel(portHandle);
   if (channel == InvalidHandleIndex) {
-    *status = PARAMETER_OUT_OF_RANGE;
+    *status = RESOURCE_OUT_OF_RANGE;
+    hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for PWM", 0,
+                                     kNumPWMChannels, channel);
     return HAL_kInvalidHandle;
   }
 
@@ -40,19 +41,22 @@ HAL_DigitalHandle HAL_InitializePWMPort(HAL_PortHandle portHandle,
     channel = remapMXPPWMChannel(channel) + 10;  // remap MXP to proper channel
   }
 
-  auto handle =
-      digitalChannelHandles->Allocate(channel, HAL_HandleEnum::PWM, status);
+  HAL_DigitalHandle handle;
+
+  auto port = digitalChannelHandles->Allocate(channel, HAL_HandleEnum::PWM,
+                                              &handle, status);
 
   if (*status != 0) {
+    if (port) {
+      hal::SetLastErrorPreviouslyAllocated(status, "PWM or DIO", channel,
+                                           port->previousAllocation);
+    } else {
+      hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for PWM", 0,
+                                       kNumPWMChannels, channel);
+    }
     return HAL_kInvalidHandle;  // failed to allocate. Pass error back.
   }
 
-  auto port = digitalChannelHandles->Get(handle, HAL_HandleEnum::PWM);
-  if (port == nullptr) {  // would only occur on thread issue.
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
-
   port->channel = origChannel;
 
   SimPWMData[origChannel].initialized = true;
@@ -60,6 +64,8 @@ HAL_DigitalHandle HAL_InitializePWMPort(HAL_PortHandle portHandle,
   // Defaults to allow an always valid config.
   HAL_SetPWMConfig(handle, 2.0, 1.501, 1.5, 1.499, 1.0, status);
 
+  port->previousAllocation = allocationLocation ? allocationLocation : "";
+
   return handle;
 }
 void HAL_FreePWMPort(HAL_DigitalHandle pwmPortHandle, int32_t* status) {

hal/src/main/native/sim/Relay.cpp

@@ -4,7 +4,10 @@
 
 #include "hal/Relay.h"
 
+#include <string>
+
 #include "HALInitializer.h"
+#include "HALInternal.h"
 #include "PortsInternal.h"
 #include "hal/handles/IndexedHandleResource.h"
 #include "mockdata/RelayDataInternal.h"
@@ -15,6 +18,7 @@ namespace {
 struct Relay {
   uint8_t channel;
   bool fwd;
+  std::string previousAllocation;
 };
 }  // namespace
 
@@ -32,6 +36,7 @@ void InitializeRelay() {
 
 extern "C" {
 HAL_RelayHandle HAL_InitializeRelayPort(HAL_PortHandle portHandle, HAL_Bool fwd,
+                                        const char* allocationLocation,
                                         int32_t* status) {
   hal::init::CheckInit();
   if (*status != 0) {
@@ -39,8 +44,10 @@ HAL_RelayHandle HAL_InitializeRelayPort(HAL_PortHandle portHandle, HAL_Bool fwd,
   }
 
   int16_t channel = getPortHandleChannel(portHandle);
-  if (channel == InvalidHandleIndex) {
-    *status = PARAMETER_OUT_OF_RANGE;
+  if (channel == InvalidHandleIndex || channel >= kNumRelayChannels) {
+    *status = RESOURCE_OUT_OF_RANGE;
+    hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for Relay", 0,
+                                     kNumRelayChannels, channel);
     return HAL_kInvalidHandle;
   }
 
@@ -48,18 +55,20 @@ HAL_RelayHandle HAL_InitializeRelayPort(HAL_PortHandle portHandle, HAL_Bool fwd,
     channel += kNumRelayHeaders;  // add 4 to reverse channels
   }
 
-  auto handle = relayHandles->Allocate(channel, status);
+  HAL_RelayHandle handle;
+  auto port = relayHandles->Allocate(channel, &handle, status);
 
   if (*status != 0) {
+    if (port) {
+      hal::SetLastErrorPreviouslyAllocated(status, "Relay", channel,
+                                           port->previousAllocation);
+    } else {
+      hal::SetLastErrorIndexOutOfRange(status, "Invalid Index for Relay", 0,
+                                       kNumRelayChannels, channel);
+    }
     return HAL_kInvalidHandle;  // failed to allocate. Pass error back.
   }
 
-  auto port = relayHandles->Get(handle);
-  if (port == nullptr) {  // would only occur on thread issue.
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
-
   if (!fwd) {
     // Subtract number of headers to put channel in range
     channel -= kNumRelayHeaders;
@@ -73,6 +82,7 @@ HAL_RelayHandle HAL_InitializeRelayPort(HAL_PortHandle portHandle, HAL_Bool fwd,
   }
 
   port->channel = static_cast<uint8_t>(channel);
+  port->previousAllocation = allocationLocation ? allocationLocation : "";
 
   return handle;
 }

hal/src/main/native/sim/Solenoid.cpp

@@ -55,17 +55,13 @@ HAL_SolenoidHandle HAL_InitializeSolenoidPort(HAL_PortHandle portHandle,
     return HAL_kInvalidHandle;
   }
 
-  auto handle = solenoidHandles->Allocate(
-      module * kNumSolenoidChannels + channel, status);
+  HAL_SolenoidHandle handle;
+  auto solenoidPort = solenoidHandles->Allocate(
+      module * kNumSolenoidChannels + channel, &handle, status);
   if (handle == HAL_kInvalidHandle) {  // out of resources
     *status = NO_AVAILABLE_RESOURCES;
     return HAL_kInvalidHandle;
   }
-  auto solenoidPort = solenoidHandles->Get(handle);
-  if (solenoidPort == nullptr) {  // would only occur on thread issues
-    *status = HAL_HANDLE_ERROR;
-    return HAL_kInvalidHandle;
-  }
   solenoidPort->module = static_cast<uint8_t>(module);
   solenoidPort->channel = static_cast<uint8_t>(channel);