[media] iguanair: explain tx carrier setup
Just comments. No functional changes.
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
diff --git a/drivers/media/rc/iguanair.c b/drivers/media/rc/iguanair.c
index fdae05c..99a3a5a 100644
--- a/drivers/media/rc/iguanair.c
+++ b/drivers/media/rc/iguanair.c
@@ -286,10 +286,10 @@
}
/*
- * The iguana ir creates the carrier by busy spinning after each pulse or
- * space. This is counted in CPU cycles, with the CPU running at 24MHz. It is
+ * The iguanair creates the carrier by busy spinning after each half period.
+ * This is counted in CPU cycles, with the CPU running at 24MHz. It is
* broken down into 7-cycles and 4-cyles delays, with a preference for
- * 4-cycle delays.
+ * 4-cycle delays, minus the overhead of the loop itself (cycle_overhead).
*/
static int iguanair_set_tx_carrier(struct rc_dev *dev, uint32_t carrier)
{
@@ -316,7 +316,14 @@
sevens = (4 - cycles) & 3;
fours = (cycles - sevens * 7) / 4;
- /* magic happens here */
+ /*
+ * The firmware interprets these values as a relative offset
+ * for a branch. Immediately following the branches, there
+ * 4 instructions of 7 cycles (2 bytes each) and 110
+ * instructions of 4 cycles (1 byte each). A relative branch
+ * of 0 will execute all of them, branch further for less
+ * cycle burning.
+ */
ir->packet->busy7 = (4 - sevens) * 2;
ir->packet->busy4 = 110 - fours;
}