subr_pidctrl.c

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