1 // SPDX-License-Identifier: GPL-2.0-or-later
3 * pid.c PID controller for testing cooling devices
5 * Copyright (C) 2012 Intel Corporation. All rights reserved.
7 * Author Name Jacob Pan <jacob.jun.pan@linux.intel.com>
15 #include <sys/types.h>
28 /**************************************************************************
29 * PID (Proportional-Integral-Derivative) controller is commonly used in
30 * linear control system, consider the process.
32 * kp = proportional gain
34 * kd = derivative gain
36 * We use type C Alan Bradley equation which takes set point off the
37 * output dependency in P and D term.
39 * y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
40 * - 2*x[k-1]+x[k-2])/Ts
43 ***********************************************************************/
44 struct pid_params p_param;
45 /* cached data from previous loop */
46 static double xk_1, xk_2; /* input temperature x[k-#] */
49 * TODO: make PID parameters tuned automatically,
50 * 1. use CPU burn to produce open loop unit step response
51 * 2. calculate PID based on Ziegler-Nichols rule
53 * add a flag for tuning PID
55 int init_thermal_controller(void)
59 p_param.ts = ticktime;
60 /* TODO: get it from TUI tuning tab */
65 p_param.t_target = target_temp_user;
70 void controller_reset(void)
72 /* TODO: relax control data when not over thermal limit */
73 syslog(LOG_DEBUG, "TC inactive, relax p-state\n");
80 /* To be called at time interval Ts. Type C PID controller.
81 * y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
82 * - 2*x[k-1]+x[k-2])/Ts
83 * TODO: add low pass filter for D term
85 #define GUARD_BAND (2)
86 void controller_handler(const double xk, double *yk)
89 double p_term, i_term, d_term;
91 ek = p_param.t_target - xk; /* error */
93 syslog(LOG_DEBUG, "PID: %3.1f Below set point %3.1f, stop\n",
94 xk, p_param.t_target);
99 /* compute intermediate PID terms */
100 p_term = -p_param.kp * (xk - xk_1);
101 i_term = p_param.kp * p_param.ki * p_param.ts * ek;
102 d_term = -p_param.kp * p_param.kd * (xk - 2 * xk_1 + xk_2) / p_param.ts;
104 *yk += p_term + i_term + d_term;
105 /* update sample data */
109 /* clamp output adjustment range */
110 if (*yk < -LIMIT_HIGH)
112 else if (*yk > -LIMIT_LOW)
117 set_ctrl_state(lround(fabs(p_param.y_k)));