diff options
Diffstat (limited to 'src/kernel/ao_freq.c')
| -rw-r--r-- | src/kernel/ao_freq.c | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/src/kernel/ao_freq.c b/src/kernel/ao_freq.c new file mode 100644 index 00000000..12496f6f --- /dev/null +++ b/src/kernel/ao_freq.c @@ -0,0 +1,55 @@ +/* + * Copyright © 2012 Keith Packard <keithp@keithp.com> + * + * 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; version 2 of the License. + * + * 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 <ao.h> + +/* + * 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; +} |