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; version 2 of the License.
8 * This program is distributed in the hope that it will be useful, but
9 * WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
11 * General Public License for more details.
13 * You should have received a copy of the GNU General Public License along
14 * with this program; if not, write to the Free Software Foundation, Inc.,
15 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
18 #if !defined(AO_CONVERT_TEST) && !defined(AO_FLIGHT_TEST)
22 #include <ao_sample.h>
24 static const ao_v_t altitude_table[] = {
28 #define ALT_FRAC_SCALE (1 << ALT_FRAC_BITS)
29 #define ALT_FRAC_MASK (ALT_FRAC_SCALE - 1)
32 ao_pres_to_altitude(int16_t pres) __reentrant
39 o = pres >> ALT_FRAC_BITS;
40 part = pres & ALT_FRAC_MASK;
42 return ((int32_t) altitude_table[o] * (ALT_FRAC_SCALE - part) +
43 (int32_t) altitude_table[o+1] * part + (ALT_FRAC_SCALE >> 1)) >> ALT_FRAC_BITS;
46 #if AO_NEED_ALTITUDE_TO_PRES
48 ao_altitude_to_pres(ao_v_t alt) __reentrant
50 ao_v_t span, sub_span;
56 while ((h - l) != 1) {
58 if (altitude_table[m] < alt)
63 span = altitude_table[l] - altitude_table[h];
64 sub_span = altitude_table[l] - alt;
65 pres = ((((int32_t) l * (span - sub_span) + (int32_t) h * sub_span) << ALT_FRAC_BITS) + (span >> 1)) / span;
70 return (int16_t) pres;
76 ao_temp_to_dC(int16_t temp) __reentrant
80 /* Output voltage at 0°C = 0.755V
81 * Coefficient = 0.00247V/°C
82 * Reference voltage = 1.25V
84 * temp = ((value / 32767) * 1.25 - 0.755) / 0.00247
85 * = (value - 19791.268) / 32768 * 1.25 / 0.00247
86 * ≃ (value - 19791) * 1012 / 65536
88 ret = ((temp - 19791) * 1012L) >> 16;