2 * Copyright © 2009 Keith Packard <keithp@keithp.com>
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful, but
10 * WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * General Public License for more details.
14 * You should have received a copy of the GNU General Public License along
15 * with this program; if not, write to the Free Software Foundation, Inc.,
16 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
19 #if !defined(AO_CONVERT_TEST) && !defined(AO_FLIGHT_TEST)
23 #include <ao_sample.h>
25 static const ao_v_t altitude_table[] = {
29 #define ALT_FRAC_SCALE (1 << ALT_FRAC_BITS)
30 #define ALT_FRAC_MASK (ALT_FRAC_SCALE - 1)
33 ao_pres_to_altitude(int16_t pres)
40 o = pres >> ALT_FRAC_BITS;
41 part = pres & ALT_FRAC_MASK;
43 return ((int32_t) altitude_table[o] * (ALT_FRAC_SCALE - part) +
44 (int32_t) altitude_table[o+1] * part + (ALT_FRAC_SCALE >> 1)) >> ALT_FRAC_BITS;
47 #if AO_NEED_ALTITUDE_TO_PRES
49 ao_altitude_to_pres(ao_v_t alt)
51 ao_v_t span, sub_span;
57 while ((h - l) != 1) {
59 if (altitude_table[m] < alt)
64 span = altitude_table[l] - altitude_table[h];
65 sub_span = altitude_table[l] - alt;
66 pres = ((((int32_t) l * (span - sub_span) + (int32_t) h * sub_span) << ALT_FRAC_BITS) + (span >> 1)) / span;
71 return (int16_t) pres;
77 ao_temp_to_dC(int16_t temp)
81 /* Output voltage at 0°C = 0.755V
82 * Coefficient = 0.00247V/°C
83 * Reference voltage = 1.25V
85 * temp = ((value / 32767) * 1.25 - 0.755) / 0.00247
86 * = (value - 19791.268) / 32768 * 1.25 / 0.00247
87 * ≃ (value - 19791) * 1012 / 65536
89 ret = ((temp - 19791) * 1012L) >> 16;