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windfarm_pid.c
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1 /*
2  * Windfarm PowerMac thermal control. Generic PID helpers
3  *
4  * (c) Copyright 2005 Benjamin Herrenschmidt, IBM Corp.
6  *
7  * Released under the term of the GNU GPL v2.
8  */
9 
10 #include <linux/types.h>
11 #include <linux/errno.h>
12 #include <linux/kernel.h>
13 #include <linux/string.h>
14 #include <linux/module.h>
15 
16 #include "windfarm_pid.h"
17 
18 #undef DEBUG
19 
20 #ifdef DEBUG
21 #define DBG(args...) printk(args)
22 #else
23 #define DBG(args...) do { } while(0)
24 #endif
25 
27 {
28  memset(st, 0, sizeof(struct wf_pid_state));
29  st->param = *param;
30  st->first = 1;
31 }
33 
34 s32 wf_pid_run(struct wf_pid_state *st, s32 new_sample)
35 {
36  s64 error, integ, deriv;
37  s32 target;
38  int i, hlen = st->param.history_len;
39 
40  /* Calculate error term */
41  error = new_sample - st->param.itarget;
42 
43  /* Get samples into our history buffer */
44  if (st->first) {
45  for (i = 0; i < hlen; i++) {
46  st->samples[i] = new_sample;
47  st->errors[i] = error;
48  }
49  st->first = 0;
50  st->index = 0;
51  } else {
52  st->index = (st->index + 1) % hlen;
53  st->samples[st->index] = new_sample;
54  st->errors[st->index] = error;
55  }
56 
57  /* Calculate integral term */
58  for (i = 0, integ = 0; i < hlen; i++)
59  integ += st->errors[(st->index + hlen - i) % hlen];
60  integ *= st->param.interval;
61 
62  /* Calculate derivative term */
63  deriv = st->errors[st->index] -
64  st->errors[(st->index + hlen - 1) % hlen];
65  deriv /= st->param.interval;
66 
67  /* Calculate target */
68  target = (s32)((integ * (s64)st->param.gr + deriv * (s64)st->param.gd +
69  error * (s64)st->param.gp) >> 36);
70  if (st->param.additive)
71  target += st->target;
72  target = max(target, st->param.min);
73  target = min(target, st->param.max);
74  st->target = target;
75 
76  return st->target;
77 }
79 
81  struct wf_cpu_pid_param *param)
82 {
83  memset(st, 0, sizeof(struct wf_cpu_pid_state));
84  st->param = *param;
85  st->first = 1;
86 }
88 
89 s32 wf_cpu_pid_run(struct wf_cpu_pid_state *st, s32 new_power, s32 new_temp)
90 {
91  s64 integ, deriv, prop;
92  s32 error, target, sval, adj;
93  int i, hlen = st->param.history_len;
94 
95  /* Calculate error term */
96  error = st->param.pmaxadj - new_power;
97 
98  /* Get samples into our history buffer */
99  if (st->first) {
100  for (i = 0; i < hlen; i++) {
101  st->powers[i] = new_power;
102  st->errors[i] = error;
103  }
104  st->temps[0] = st->temps[1] = new_temp;
105  st->first = 0;
106  st->index = st->tindex = 0;
107  } else {
108  st->index = (st->index + 1) % hlen;
109  st->powers[st->index] = new_power;
110  st->errors[st->index] = error;
111  st->tindex = (st->tindex + 1) % 2;
112  st->temps[st->tindex] = new_temp;
113  }
114 
115  /* Calculate integral term */
116  for (i = 0, integ = 0; i < hlen; i++)
117  integ += st->errors[(st->index + hlen - i) % hlen];
118  integ *= st->param.interval;
119  integ *= st->param.gr;
120  sval = st->param.tmax - (s32)(integ >> 20);
121  adj = min(st->param.ttarget, sval);
122 
123  DBG("integ: %lx, sval: %lx, adj: %lx\n", integ, sval, adj);
124 
125  /* Calculate derivative term */
126  deriv = st->temps[st->tindex] -
127  st->temps[(st->tindex + 2 - 1) % 2];
128  deriv /= st->param.interval;
129  deriv *= st->param.gd;
130 
131  /* Calculate proportional term */
132  prop = st->last_delta = (new_temp - adj);
133  prop *= st->param.gp;
134 
135  DBG("deriv: %lx, prop: %lx\n", deriv, prop);
136 
137  /* Calculate target */
138  target = st->target + (s32)((deriv + prop) >> 36);
139  target = max(target, st->param.min);
140  target = min(target, st->param.max);
141  st->target = target;
142 
143  return st->target;
144 }
146 
147 MODULE_AUTHOR("Benjamin Herrenschmidt <[email protected]>");
148 MODULE_DESCRIPTION("PID algorithm for PowerMacs thermal control");
149 MODULE_LICENSE("GPL");