altos: Rename 'core' to 'kernel'

[fw/altos] / src / kernel / ao_freq.c

diff --git a/src/kernel/ao_freq.c b/src/kernel/ao_freq.c
new file mode 100644 (file)
index 0000000..12496f6
--- /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;
+}