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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 * 2pi, f24.8. */
uint32_t postrack_footing_2pi;
/** Precomputed footing factor, f8.24.
 * postrack_footing_factor = (1/2pi * 256) / postrack_footing
 * Explanations:
 *  - Angles are between 0 and 1, corresponding to 0 and 2pi, therefore we
 *  must divide by 2pi to convert unit (Arc=Angle * Radius only works for
 *  radians).
 *  - dd (see postrack_update) is in f11.16 format, we multiply by 256 to have
 *  a angle in f8.24 format.
 *  - this factor is in f8.24 format, therefore, 1 is writen (1L << 24). */
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 (0x1837);
}

#define M_PI		3.14159265358979323846	/* pi */

/** Update the current position. */
static inline void
postrack_update (void)
{
    int32_t d, dd, da, na, dsc;
    d = counter_right_diff + counter_left_diff;		/* 10b */
    d <<= 16;						/* 10.16b */
    d >>= 1;						/* 9.16b */
    if (counter_right_diff == counter_left_diff)
      {
	/* Line. */
	postrack_x += dsp_mul_f824 (d, dsp_cos_f824 (postrack_a)) >> 8;
	postrack_y += dsp_mul_f824 (d, dsp_sin_f824 (postrack_a)) >> 8;
      }
    else
      {
	/* Arc. */
	dd = counter_right_diff - counter_left_diff;	/* 10b */
	dd <<= 16;					/* 10.16b */
	da = dsp_mul_f824 (dd, postrack_footing_factor);/* 8.24b */
	/* New angle. */
	na = postrack_a + da;
	/* Compute da in radians. */
	da = dsp_mul_f824 (da, 2 * M_PI * (1L << 24));
	/* X increment. */
	dsc = dsp_sin_f824 (na) - dsp_sin_f824 (postrack_a);	/* 8.24b */
	dsc = dsp_div_f824 (dsc, da);			/* 8.24b < 1 */
	postrack_x += dsp_mul_f824 (d, dsc) >> 8;	/* 24.8b */
	/* Y increment. */
	dsc = dsp_cos_f824 (postrack_a) - dsp_cos_f824 (na);	/* 8.24b */
	dsc = dsp_div_f824 (dsc, da);			/* 8.24b < 1 */
	postrack_y += dsp_mul_f824 (d, dsc) >> 8;	/* 24.8b */
	/* Angle update. */
	postrack_a = na;
	postrack_a &= 0x00ffffff;
      }
}

#define M_1_PI		0.31830988618379067154	/* 1/pi */

/** Change the footing value. */
static inline void
postrack_set_footing (uint16_t footing)
{
    postrack_footing = footing;
    postrack_footing_2pi = (uint32_t) (M_PI * 2 * 255) * footing;
    postrack_footing_factor =
	(int32_t) (0.5 * M_1_PI * (1L << 8) * (1L << 24)) / footing;
}