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/* postrack.c */
/* asserv - Position & speed motor control on a ATmega128. {{{
 *
 * Copyright (C) 2004 Nicolas Schodet
 *
 * Robot APB Team/Efrei 2005.
 *        Web: http://assos.efrei.fr/robot/
 *      Email: robot AT efrei DOT fr
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * }}} */

/** Current position, f24.8. */
int32_t postrack_x, postrack_y;
/** Current angle, f8.24. */
int32_t postrack_a;
/** Distance between the weels, u16. */
uint16_t postrack_footing;
/** Precomputed footing factor, f8.24.
 * postrack_footing_factor = 1 / postrack_footing */
int32_t postrack_footing_factor;

/* +AutoDec */

/** Initialise the position tracker. */
static inline void
postrack_init (void);

/** Update the current position. */
static inline void
postrack_update (void);

/** Change the footing value. */
static inline void
postrack_set_footing (uint16_t footing);

/* -AutoDec */

/** Initialise the position tracker. */
static inline void
postrack_init (void)
{
    postrack_set_footing (5000);
}

/** Update the current position. */
static inline void
postrack_update (void)
{
    int32_t d, dd, da, r, na;
    d = counter_right_diff + counter_left_diff;
    d <<= 24 - 1;
    if (counter_right_diff == counter_left_diff)
      {
	postrack_x += dsp_mul_f824 (d, dsp_cos (postrack_a)) >> 16;
	postrack_y += dsp_mul_f824 (d, dsp_sin (postrack_a)) >> 16;
      }
    else
      {
	/* XXX: WARNING: dleft & dright 16 bits?
	 * This code should not work at high speed (> 127). */
	dd = counter_right_diff - counter_left_diff;
	dd <<= 24;
	da = dsp_mul_f824 (postrack_footing_factor, dd);
	r = dsp_div_f824 (d, da);
	na = postrack_a + da;
	postrack_x +=
	    dsp_mul_f824 (r, dsp_sin (na) - dsp_sin (postrack_a)) >> 16;
	postrack_y +=
	    dsp_mul_f824 (r, dsp_cos (postrack_a) - dsp_cos (na)) >> 16;
	postrack_a = na;
      }
}

/** Change the footing value. */
static inline void
postrack_set_footing (uint16_t footing)
{
    postrack_footing = footing;
    postrack_footing_factor = (1L << 24) / footing;
}