/* postrack.c - Compute current position from counters. */ /* asserv - Position & speed motor control on AVR. {{{ * * Copyright (C) 2006 Nicolas Schodet * * APBTeam: * Web: http://apbteam.org/ * Email: team AT apbteam DOT org * * 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. * * }}} */ #include "common.h" #include "postrack.h" #include "modules/math/fixed/fixed.h" #include "modules/math/math.h" #include "cs.h" /** 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 = (1/2pi * 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 f10.16 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). */ static uint32_t postrack_footing_factor; /** Initialise the position tracker. */ void postrack_init (void) { /* Prevent division by 0 by providing a default large value. */ postrack_set_footing (0x1000); } /** Update the current position. */ void postrack_update (void) { int32_t d, dd, da, na, dsc; d = encoder_right.diff + encoder_left.diff; /* 10b */ d <<= 16; /* 10.16b */ if (encoder_right.diff == encoder_left.diff) { /* Line. */ postrack_x += fixed_mul_f824 (d, fixed_cos_f824 (postrack_a)) >> 8; postrack_y += fixed_mul_f824 (d, fixed_sin_f824 (postrack_a)) >> 8; } else { /* Arc. */ dd = encoder_right.diff - encoder_left.diff; /* 10b */ dd <<= 16; /* 10.16b */ da = fixed_mul_f824 (dd, postrack_footing_factor);/* 8.24b */ /* New angle. */ na = postrack_a + da; /* Compute da in radians. */ da = fixed_mul_f824 (da, 2 * M_PI * (1L << 24)); /* X increment. */ dsc = fixed_sin_f824 (na) - fixed_sin_f824 (postrack_a); /* 8.24b */ dsc = fixed_div_f824 (dsc, da); /* 8.24b < 1 */ postrack_x += fixed_mul_f824 (d, dsc) >> 8; /* 24.8b */ /* Y increment. */ dsc = fixed_cos_f824 (postrack_a) - fixed_cos_f824 (na); /* 8.24b */ dsc = fixed_div_f824 (dsc, da); /* 8.24b < 1 */ postrack_y += fixed_mul_f824 (d, dsc) >> 8; /* 24.8b */ /* Angle update. */ postrack_a = na; postrack_a &= 0x00ffffff; } } /** Change the footing value. */ void postrack_set_footing (uint16_t footing) { postrack_footing = footing; postrack_footing_factor = (uint32_t) (0.5 * M_1_PI * (1L << 8) * (1L << 24)) / footing; }