PID Objects & Algo
These are the PID controller implementations for fans,
and thermals. This also includes the PID algorithm used.
Change-Id: I30471fbf7a8a7ed65f78bf105970d62815fedc56
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/pid/ec/pid.cpp b/pid/ec/pid.cpp
new file mode 100644
index 0000000..a1c4e41
--- /dev/null
+++ b/pid/ec/pid.cpp
@@ -0,0 +1,118 @@
+/**
+ * Copyright 2017 Google Inc.
+ *
+ * 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 "pid.hpp"
+
+namespace ec
+{
+
+/********************************
+ * clamp
+ *
+ */
+static float clamp(float x, float min, float max)
+{
+ if (x < min)
+ {
+ return min;
+ }
+ else if (x > max)
+ {
+ return max;
+ }
+ return x;
+}
+
+/********************************
+ * pid code
+ * Note: Codes assumes the ts field is non-zero
+ */
+float pid(pid_info_t* pidinfoptr, float input, float setpoint)
+{
+ float error;
+
+ float p_term = 0.0f;
+ float i_term = 0.0f;
+ float ff_term = 0.0f;
+
+ float output;
+
+ // calculate P, I, D, FF
+
+ // Pid
+ error = setpoint - input;
+ p_term = pidinfoptr->p_c * error;
+
+ // pId
+ if (0.0f != pidinfoptr->i_c)
+ {
+ i_term = pidinfoptr->integral;
+ i_term += error * pidinfoptr->i_c * pidinfoptr->ts;
+ i_term = clamp(i_term, pidinfoptr->i_lim.min, pidinfoptr->i_lim.max);
+ }
+
+ // FF
+ ff_term = (setpoint + pidinfoptr->ff_off) * pidinfoptr->ff_gain;
+
+ output = p_term + i_term + ff_term;
+ output = clamp(output, pidinfoptr->out_lim.min, pidinfoptr->out_lim.max);
+
+ // slew rate
+ // TODO(aarena) - Simplify logic as Andy suggested by creating dynamic
+ // out_lim_min/max that are affected by slew rate control and just clamping
+ // to those instead of effectively clamping twice.
+ if (pidinfoptr->initialized)
+ {
+ if (pidinfoptr->slew_neg != 0.0f)
+ {
+ // Don't decrease too fast
+ float min_out = pidinfoptr->last_output + pidinfoptr->slew_neg *
+ pidinfoptr->ts;
+ if (output < min_out)
+ {
+ output = min_out;
+ }
+ }
+ if (pidinfoptr->slew_pos != 0.0f)
+ {
+ // Don't increase too fast
+ float max_out = pidinfoptr->last_output + pidinfoptr->slew_pos *
+ pidinfoptr->ts;
+ if (output > max_out)
+ {
+ output = max_out;
+ }
+ }
+
+ if (pidinfoptr->slew_neg != 0.0f || pidinfoptr->slew_pos != 0.0f)
+ {
+ // Back calculate integral term for the cases where we limited the
+ // output
+ i_term = output - p_term;
+ }
+ }
+
+ // Clamp again because having limited the output may result in a
+ // larger integral term
+ i_term = clamp(i_term, pidinfoptr->i_lim.min, pidinfoptr->i_lim.max);
+ pidinfoptr->integral = i_term;
+ pidinfoptr->initialized = true;
+ pidinfoptr->last_output = output;
+
+ return output;
+}
+
+}
diff --git a/pid/ec/pid.hpp b/pid/ec/pid.hpp
new file mode 100644
index 0000000..e138933
--- /dev/null
+++ b/pid/ec/pid.hpp
@@ -0,0 +1,53 @@
+#pragma once
+
+#include <cstdint>
+
+namespace ec
+{
+
+typedef struct
+{
+ float min;
+ float max;
+} limits_t;
+
+/* Note: If you update these structs you need to update the copy code in
+ * pid/util.cpp.
+ */
+typedef struct
+{
+ bool initialized; // has pid been initialized
+
+ float ts; // sample time in seconds
+ float integral; // intergal of error
+ float last_output; // value of last output
+
+ float p_c; // coeff for P
+ float i_c; // coeff for I
+ float ff_off; // offset coeff for feed-forward term
+ float ff_gain; // gain for feed-forward term
+
+ limits_t i_lim; // clamp of integral
+ limits_t out_lim; // clamp of output
+ float slew_neg;
+ float slew_pos;
+} pid_info_t;
+
+float pid(pid_info_t* pidinfoptr, float input, float setpoint);
+
+/* Condensed version for use by the configuration. */
+struct pidinfo
+{
+ float ts; // sample time in seconds
+ float p_c; // coeff for P
+ float i_c; // coeff for I
+ float ff_off; // offset coeff for feed-forward term
+ float ff_gain; // gain for feed-forward term
+ ec::limits_t i_lim; // clamp of integral
+ ec::limits_t out_lim; // clamp of output
+ float slew_neg;
+ float slew_pos;
+};
+
+
+}