1 files changed, 63 insertions, 0 deletions
diff --git a/src/core/lib/transport/pid_controller.cc b/src/core/lib/transport/pid_controller.cc
new file mode 100644
index 0000000000..4b304f17b2
--- /dev/null
+++ b/src/core/lib/transport/pid_controller.cc
@@ -0,0 +1,63 @@
+/*
+ *
+ * Copyright 2016 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include "src/core/lib/transport/pid_controller.h"
+#include <grpc/support/useful.h>
+
+void grpc_pid_controller_init(grpc_pid_controller *pid_controller,
+                              grpc_pid_controller_args args) {
+  pid_controller->args = args;
+  pid_controller->last_control_value = args.initial_control_value;
+  grpc_pid_controller_reset(pid_controller);
+}
+
+void grpc_pid_controller_reset(grpc_pid_controller *pid_controller) {
+  pid_controller->last_error = 0.0;
+  pid_controller->last_dc_dt = 0.0;
+  pid_controller->error_integral = 0.0;
+}
+
+double grpc_pid_controller_update(grpc_pid_controller *pid_controller,
+                                  double error, double dt) {
+  if (dt == 0) return pid_controller->last_control_value;
+  /* integrate error using the trapezoid rule */
+  pid_controller->error_integral +=
+      dt * (pid_controller->last_error + error) * 0.5;
+  pid_controller->error_integral = GPR_CLAMP(
+      pid_controller->error_integral, -pid_controller->args.integral_range,
+      pid_controller->args.integral_range);
+  double diff_error = (error - pid_controller->last_error) / dt;
+  /* calculate derivative of control value vs time */
+  double dc_dt = pid_controller->args.gain_p * error +
+                 pid_controller->args.gain_i * pid_controller->error_integral +
+                 pid_controller->args.gain_d * diff_error;
+  /* and perform trapezoidal integration */
+  double new_control_value = pid_controller->last_control_value +
+                             dt * (pid_controller->last_dc_dt + dc_dt) * 0.5;
+  new_control_value =
+      GPR_CLAMP(new_control_value, pid_controller->args.min_control_value,
+                pid_controller->args.max_control_value);
+  pid_controller->last_error = error;
+  pid_controller->last_dc_dt = dc_dt;
+  pid_controller->last_control_value = new_control_value;
+  return new_control_value;
+}
+
+double grpc_pid_controller_last(grpc_pid_controller *pid_controller) {
+  return pid_controller->last_control_value;
+}