1 /* 2 * pid.c PID controller for testing cooling devices 3 * 4 * 5 * 6 * Copyright (C) 2012 Intel Corporation. All rights reserved. 7 * 8 * This program is free software; you can redistribute it and/or 9 * modify it under the terms of the GNU General Public License version 10 * 2 or later as published by the Free Software Foundation. 11 * 12 * This program is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15 * GNU General Public License for more details. 16 * 17 * Author Name Jacob Pan <jacob.jun.pan@linux.intel.com> 18 * 19 */ 20 21 #include <unistd.h> 22 #include <stdio.h> 23 #include <stdlib.h> 24 #include <string.h> 25 #include <stdint.h> 26 #include <sys/types.h> 27 #include <dirent.h> 28 #include <libintl.h> 29 #include <ctype.h> 30 #include <assert.h> 31 #include <time.h> 32 #include <limits.h> 33 #include <math.h> 34 #include <sys/stat.h> 35 #include <syslog.h> 36 37 #include "tmon.h" 38 39 /************************************************************************** 40 * PID (Proportional-Integral-Derivative) controller is commonly used in 41 * linear control system, consider the the process. 42 * G(s) = U(s)/E(s) 43 * kp = proportional gain 44 * ki = integral gain 45 * kd = derivative gain 46 * Ts 47 * We use type C Alan Bradley equation which takes set point off the 48 * output dependency in P and D term. 49 * 50 * y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k] 51 * - 2*x[k-1]+x[k-2])/Ts 52 * 53 * 54 ***********************************************************************/ 55 struct pid_params p_param; 56 /* cached data from previous loop */ 57 static double xk_1, xk_2; /* input temperature x[k-#] */ 58 59 /* 60 * TODO: make PID parameters tuned automatically, 61 * 1. use CPU burn to produce open loop unit step response 62 * 2. calculate PID based on Ziegler-Nichols rule 63 * 64 * add a flag for tuning PID 65 */ 66 int init_thermal_controller(void) 67 { 68 int ret = 0; 69 70 /* init pid params */ 71 p_param.ts = ticktime; 72 /* TODO: get it from TUI tuning tab */ 73 p_param.kp = .36; 74 p_param.ki = 5.0; 75 p_param.kd = 0.19; 76 77 p_param.t_target = target_temp_user; 78 79 return ret; 80 } 81 82 void controller_reset(void) 83 { 84 /* TODO: relax control data when not over thermal limit */ 85 syslog(LOG_DEBUG, "TC inactive, relax p-state\n"); 86 p_param.y_k = 0.0; 87 xk_1 = 0.0; 88 xk_2 = 0.0; 89 set_ctrl_state(0); 90 } 91 92 /* To be called at time interval Ts. Type C PID controller. 93 * y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k] 94 * - 2*x[k-1]+x[k-2])/Ts 95 * TODO: add low pass filter for D term 96 */ 97 #define GUARD_BAND (2) 98 void controller_handler(const double xk, double *yk) 99 { 100 double ek; 101 double p_term, i_term, d_term; 102 103 ek = p_param.t_target - xk; /* error */ 104 if (ek >= 3.0) { 105 syslog(LOG_DEBUG, "PID: %3.1f Below set point %3.1f, stop\n", 106 xk, p_param.t_target); 107 controller_reset(); 108 *yk = 0.0; 109 return; 110 } 111 /* compute intermediate PID terms */ 112 p_term = -p_param.kp * (xk - xk_1); 113 i_term = p_param.kp * p_param.ki * p_param.ts * ek; 114 d_term = -p_param.kp * p_param.kd * (xk - 2 * xk_1 + xk_2) / p_param.ts; 115 /* compute output */ 116 *yk += p_term + i_term + d_term; 117 /* update sample data */ 118 xk_1 = xk; 119 xk_2 = xk_1; 120 121 /* clamp output adjustment range */ 122 if (*yk < -LIMIT_HIGH) 123 *yk = -LIMIT_HIGH; 124 else if (*yk > -LIMIT_LOW) 125 *yk = -LIMIT_LOW; 126 127 p_param.y_k = *yk; 128 129 set_ctrl_state(lround(fabs(p_param.y_k))); 130 131 } 132