+/*
+ * Farnsworth spacing
+ *
+ * From: http://www.arrl.org/files/file/Technology/x9004008.pdf
+ *
+ * c: character rate in wpm
+ * s: overall rate in wpm
+ * u: unit rate (dit speed)
+ *
+ * dit: u
+ * dah: 3u
+ * intra-character-time: u
+ *
+ * u = 1.2/c
+ *
+ * Because our clock runs at 10ms, we'll round up to 70ms for u, which
+ * is about 17wpm
+ *
+ * Farnsworth adds space between characters and
+ * words:
+ * 60 c - 37.2 s
+ * Ta = -------------
+ * sc
+ *
+ * 3 Ta
+ * Tc = ----
+ * 19
+ *
+ * 7 Ta
+ * Tw = ----
+ * 19
+ *
+ * Ta = total delay to add to the characters (31 units)
+ * of a standard 50-unit "word", in seconds
+ *
+ * Tc = period between characters, in seconds
+ *
+ * Tw = period between words, in seconds
+ *
+ * We'll use Farnsworth spacing with c=18 and s=12:
+ *
+ * u = 1.2/18 = 0.0667
+ *
+ * Ta = (60 * 17 - 37.2 * 12) / (17 * 12) = 2.812
+ *
+ * Tc = 3 * Ta / 19 = .444
+ *
+ * Tw = 1.036
+ *
+ * Note that the values below are all reduced by 10ms; that's because
+ * the timer always adds a tick to make sure the task actually sleeps
+ * at least as long as the argument.
+ */
+