/* * Copyright © 2012 Keith Packard * * 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 /* * The provided 'calibration' value is * that needed to tune the radio to precisely 434550kHz. * Use that to 'walk' to the target frequency by following * a 'bresenham' line from 434550kHz to the target * frequency, and updating the radio setting along the way */ int32_t ao_freq_to_set(int32_t freq, int32_t cal) __reentrant { static __pdata int32_t set; static __pdata uint8_t neg; static __pdata int32_t error; set = 0; neg = 0; error = -434550 / 2; if ((freq -= 434550) < 0) { neg = 1; freq = -freq; } for (;;) { if (error > 0) { error -= 434550; set++; } else { error += cal; if (--freq < 0) break; } } if (neg) set = -set; return cal + set; }