e768070ca9
controller that tries to handle early invocations of the controller, in other words, invocations before the expected end of the interval. However, there were some calculation errors in this early invocation case. Notably, if an early invocation occurred while the error was negative, the derivative term was off by a large amount. One visible effect of this error was that processes were being killed by the virtual memory system's OOM killer when in fact there was plentiful free memory. Correct a couple minor errors in the sysctl descriptions, and apply some style fixes. Reviewed by: jeff, markj
158 lines
5.4 KiB
C
158 lines
5.4 KiB
C
/*-
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* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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*
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* Copyright (c) 2017, Jeffrey Roberson <jeff@freebsd.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include <sys/kernel.h>
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#include <sys/systm.h>
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#include <sys/sysctl.h>
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#include <sys/pidctrl.h>
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void
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pidctrl_init(struct pidctrl *pc, int interval, int setpoint, int bound,
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int Kpd, int Kid, int Kdd)
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{
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bzero(pc, sizeof(*pc));
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pc->pc_setpoint = setpoint;
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pc->pc_interval = interval;
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pc->pc_bound = bound * setpoint * Kid;
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pc->pc_Kpd = Kpd;
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pc->pc_Kid = Kid;
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pc->pc_Kdd = Kdd;
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}
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void
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pidctrl_init_sysctl(struct pidctrl *pc, struct sysctl_oid_list *parent)
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{
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SYSCTL_ADD_INT(NULL, parent, OID_AUTO, "error", CTLFLAG_RD,
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&pc->pc_error, 0, "Current difference from setpoint value (P)");
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SYSCTL_ADD_INT(NULL, parent, OID_AUTO, "olderror", CTLFLAG_RD,
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&pc->pc_olderror, 0, "Error value from last interval");
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SYSCTL_ADD_INT(NULL, parent, OID_AUTO, "integral", CTLFLAG_RD,
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&pc->pc_integral, 0, "Accumulated error integral (I)");
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SYSCTL_ADD_INT(NULL, parent, OID_AUTO, "derivative", CTLFLAG_RD,
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&pc->pc_derivative, 0, "Error derivative (D)");
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SYSCTL_ADD_INT(NULL, parent, OID_AUTO, "input", CTLFLAG_RD,
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&pc->pc_input, 0, "Last controller process variable input");
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SYSCTL_ADD_INT(NULL, parent, OID_AUTO, "output", CTLFLAG_RD,
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&pc->pc_output, 0, "Last controller output");
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SYSCTL_ADD_INT(NULL, parent, OID_AUTO, "ticks", CTLFLAG_RD,
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&pc->pc_ticks, 0, "Last controller runtime");
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SYSCTL_ADD_INT(NULL, parent, OID_AUTO, "setpoint", CTLFLAG_RW,
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&pc->pc_setpoint, 0, "Desired level for process variable");
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SYSCTL_ADD_INT(NULL, parent, OID_AUTO, "interval", CTLFLAG_RD,
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&pc->pc_interval, 0, "Interval between calculations (ticks)");
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SYSCTL_ADD_INT(NULL, parent, OID_AUTO, "bound", CTLFLAG_RW,
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&pc->pc_bound, 0, "Integral wind-up limit");
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SYSCTL_ADD_INT(NULL, parent, OID_AUTO, "kpd", CTLFLAG_RW,
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&pc->pc_Kpd, 0, "Inverse of proportional gain");
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SYSCTL_ADD_INT(NULL, parent, OID_AUTO, "kid", CTLFLAG_RW,
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&pc->pc_Kid, 0, "Inverse of integral gain");
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SYSCTL_ADD_INT(NULL, parent, OID_AUTO, "kdd", CTLFLAG_RW,
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&pc->pc_Kdd, 0, "Inverse of derivative gain");
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}
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int
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pidctrl_classic(struct pidctrl *pc, int input)
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{
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int output, error;
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int Kpd, Kid, Kdd;
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error = pc->pc_setpoint - input;
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pc->pc_ticks = ticks;
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pc->pc_olderror = pc->pc_error;
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/* Fetch gains and prevent divide by zero. */
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Kpd = MAX(pc->pc_Kpd, 1);
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Kid = MAX(pc->pc_Kid, 1);
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Kdd = MAX(pc->pc_Kdd, 1);
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/* Compute P (proportional error), I (integral), D (derivative). */
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pc->pc_error = error;
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pc->pc_integral =
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MAX(MIN(pc->pc_integral + error, pc->pc_bound), -pc->pc_bound);
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pc->pc_derivative = error - pc->pc_olderror;
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/* Divide by inverse gain values to produce output. */
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output = (pc->pc_error / Kpd) + (pc->pc_integral / Kid) +
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(pc->pc_derivative / Kdd);
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/* Save for sysctl. */
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pc->pc_output = output;
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pc->pc_input = input;
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return (output);
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}
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int
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pidctrl_daemon(struct pidctrl *pc, int input)
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{
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int output, error;
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int Kpd, Kid, Kdd;
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error = pc->pc_setpoint - input;
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/*
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* When ticks expires we reset our variables and start a new
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* interval. If we're called multiple times during one interval
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* we attempt to report a target as if the entire error came at
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* the interval boundary.
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*/
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if ((u_int)ticks - pc->pc_ticks >= pc->pc_interval) {
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pc->pc_ticks = ticks;
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pc->pc_olderror = pc->pc_error;
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pc->pc_output = pc->pc_error = 0;
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} else {
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/* Calculate the error relative to the last call. */
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error -= pc->pc_error - pc->pc_output;
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}
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/* Fetch gains and prevent divide by zero. */
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Kpd = MAX(pc->pc_Kpd, 1);
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Kid = MAX(pc->pc_Kid, 1);
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Kdd = MAX(pc->pc_Kdd, 1);
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/* Compute P (proportional error), I (integral), D (derivative). */
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pc->pc_error += error;
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pc->pc_integral =
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MAX(MIN(pc->pc_integral + error, pc->pc_bound), 0);
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pc->pc_derivative = pc->pc_error - pc->pc_olderror;
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/* Divide by inverse gain values to produce output. */
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output = (error / Kpd) + (pc->pc_integral / Kid) +
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(pc->pc_derivative / Kdd);
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output = MAX(output - pc->pc_output, 0);
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/* Save for sysctl. */
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pc->pc_output += output;
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pc->pc_input = input;
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return (output);
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}
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