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 #ifndef AO_CONVERT_TEST
22 static const int16_t altitude_table[] = {
26 #define ALT_FRAC_SCALE (1 << ALT_FRAC_BITS)
27 #define ALT_FRAC_MASK (ALT_FRAC_SCALE - 1)
30 ao_pres_to_altitude(int16_t pres) __reentrant
37 o = pres >> ALT_FRAC_BITS;
38 part = pres & ALT_FRAC_MASK;
40 return ((int32_t) altitude_table[o] * (ALT_FRAC_SCALE - part) +
41 (int32_t) altitude_table[o+1] * part + (ALT_FRAC_SCALE >> 1)) >> ALT_FRAC_BITS;
45 ao_altitude_to_pres(int16_t alt) __reentrant
47 int16_t span, sub_span;
53 while ((h - l) != 1) {
55 if (altitude_table[m] < alt)
60 span = altitude_table[l] - altitude_table[h];
61 sub_span = altitude_table[l] - alt;
62 pres = ((((int32_t) l * (span - sub_span) + (int32_t) h * sub_span) << ALT_FRAC_BITS) + (span >> 1)) / span;
67 return (int16_t) pres;
71 ao_temp_to_dC(int16_t temp) __reentrant
75 /* Output voltage at 0°C = 0.755V
76 * Coefficient = 0.00247V/°C
77 * Reference voltage = 1.25V
79 * temp = ((value / 32767) * 1.25 - 0.755) / 0.00247
80 * = (value - 19791.268) / 32768 * 1.25 / 0.00247
81 * ≃ (value - 19791) * 1012 / 65536
83 ret = ((temp - 19791) * 1012L) >> 16;