+#ifdef WAIT_LASER
+/* val is 12 bits. Return the 16 bits value that includes the 4 bits
+ * cksum in MSB. */
+static uint16_t do_cksum(uint16_t val)
+{
+ uint16_t x, cksum;
+
+ x = (val & 0xfff);
+ /* add the three 4-bits blocks of x together */
+ cksum = x & 0xf;
+ x = x >> 4;
+ cksum += x & 0xf;
+ cksum = (cksum & 0xf) + ((cksum & 0xf0) >> 4);
+ x = x >> 4;
+ cksum += x & 0xf;
+ cksum = (cksum & 0xf) + ((cksum & 0xf0) >> 4);
+ cksum = (~cksum) & 0xf;
+ return (cksum << 12) + (val & 0xfff);
+}
+
+/* get the frame from laser time difference, return 0 on error (this
+ * frame cannot be sent). */
+static uint32_t get_frame(uint16_t laserdiff)
+{
+ uint32_t frame = 0;
+ uint16_t frame_dist = 256;
+ uint16_t step, val;
+
+ /* for calibration, return the time */
+ if (0)
+ return laserdiff;
+
+ for (step = 128; step != 0; step /= 2) {
+ val = pgm_read_word(&framedist_table[frame_dist]);
+ if (laserdiff > val)
+ frame_dist -= step;
+ else
+ frame_dist += step;
+ }
+
+ frame |= ((uint32_t)(frame_dist & FRAME_DATA_MASK) << FRAME_DATA_SHIFT);
+
+ /* process cksum and return */
+ return do_cksum(frame);
+}
+