path: root/src/modules/systemlib/pwm_limit/pwm_limit.c

/****************************************************************************
 *
 *   Copyright (c) 2013, 2014 PX4 Development Team. All rights reserved.
 *   Author: Julian Oes <joes@student.ethz.ch>
 *
 * 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.
 * 3. Neither the name PX4 nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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
 * COPYRIGHT OWNER 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.
 *
 ****************************************************************************/

/**
 * @file pwm_limit.c
 *
 * Lib to limit PWM output
 *
 * @author Julian Oes <joes@student.ethz.ch>
 */

#include "pwm_limit.h"
#include <math.h>
#include <stdbool.h>
#include <drivers/drv_hrt.h>
#include <stdio.h>

void pwm_limit_init(pwm_limit_t *limit)
{
	limit->state = PWM_LIMIT_STATE_INIT;
	limit->time_armed = 0;
	return;
}

void pwm_limit_calc(const bool armed, const unsigned num_channels, const uint16_t *disarmed_pwm, const uint16_t *min_pwm, const uint16_t *max_pwm, const float *output, uint16_t *effective_pwm, pwm_limit_t *limit)
{

	/* first evaluate state changes */
	switch (limit->state) {
		case PWM_LIMIT_STATE_INIT:

			if (armed) {

				/* set arming time for the first call */
				if (limit->time_armed == 0) {
					limit->time_armed = hrt_absolute_time();
				}

				if (hrt_elapsed_time(&limit->time_armed) >= INIT_TIME_US) {
					limit->state = PWM_LIMIT_STATE_OFF;
				}
			}
			break;
		case PWM_LIMIT_STATE_OFF:
			if (armed) {
				limit->state = PWM_LIMIT_STATE_RAMP;

				/* reset arming time, used for ramp timing */
				limit->time_armed = hrt_absolute_time();
			}
			break;
		case PWM_LIMIT_STATE_RAMP:
			if (!armed) {
				limit->state = PWM_LIMIT_STATE_OFF;
			} else if (hrt_elapsed_time(&limit->time_armed) >= RAMP_TIME_US) {
				limit->state = PWM_LIMIT_STATE_ON;
			}
			break;
		case PWM_LIMIT_STATE_ON:
			if (!armed) {
				limit->state = PWM_LIMIT_STATE_OFF;
			}
			break;
		default:
			break;
	}

	unsigned progress;

	/* then set effective_pwm based on state */
	switch (limit->state) {
		case PWM_LIMIT_STATE_OFF:
		case PWM_LIMIT_STATE_INIT:
			for (unsigned i=0; i<num_channels; i++) {
				effective_pwm[i] = disarmed_pwm[i];
			}
			break;
		case PWM_LIMIT_STATE_RAMP:
			{
				hrt_abstime diff = hrt_elapsed_time(&limit->time_armed);

				progress = diff * 10000 / RAMP_TIME_US;

				for (unsigned i=0; i<num_channels; i++) {
	                
					uint16_t ramp_min_pwm;
	                
					/* if a disarmed pwm value was set, blend between disarmed and min */
					if (disarmed_pwm[i] > 0) {

						/* safeguard against overflows */
						unsigned disarmed = disarmed_pwm[i];
						if (disarmed > min_pwm[i]) {
							disarmed = min_pwm[i];
						}

						unsigned disarmed_min_diff = min_pwm[i] - disarmed;
						ramp_min_pwm = disarmed + (disarmed_min_diff * progress) / 10000;

					} else {
	                    
						/* no disarmed pwm value set, choose min pwm */
						ramp_min_pwm = min_pwm[i];
					}

					effective_pwm[i] = output[i] * (max_pwm[i] - ramp_min_pwm)/2 + (max_pwm[i] + ramp_min_pwm)/2;

					/* last line of defense against invalid inputs */
					if (effective_pwm[i] < ramp_min_pwm) {
						effective_pwm[i] = ramp_min_pwm;
					} else if (effective_pwm[i] > max_pwm[i]) {
						effective_pwm[i] = max_pwm[i];
					}
				}
			}
			break;
		case PWM_LIMIT_STATE_ON:
			for (unsigned i=0; i<num_channels; i++) {
				effective_pwm[i] = output[i] * (max_pwm[i] - min_pwm[i])/2 + (max_pwm[i] + min_pwm[i])/2;

				/* last line of defense against invalid inputs */
				if (effective_pwm[i] < min_pwm[i]) {
					effective_pwm[i] = min_pwm[i];
				} else if (effective_pwm[i] > max_pwm[i]) {
					effective_pwm[i] = max_pwm[i];
				}
			}
			break;
		default:
			break;
	}
	return;
}