+/*
+ * 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;
+}