MFC r286469, r286591, r286595, r286596, r286613:

  Provide the tty-layer mutex when initializing the pps api.  This allows
  time_pps_fetch() to be used in blocking mode.

  Allow the choice of PPS signal captured by uart(4) to be runtime-configured,
  eliminating the need to build a custom kernel to use the CTS signal.

  Correct the polarity of the PPS assert and clear events with respect to the
  electrical signals on the serial port.

  Document the change in polarity of the uart(4) PPS capture.

  Style fix -- do the braces for switches correctly.

Relnotes:	yes

1 files changed, 14 insertions, 0 deletions

diff --git a/UPDATING b/UPDATING
index 3263818..5f0b398 100644
--- a/UPDATING
+++ b/UPDATING
@@ -16,6 +16,20 @@ from older versions of FreeBSD, try WITHOUT_CLANG to bootstrap to the tip of
 stable/10, and then rebuild without this option. The bootstrap process from
 older version of current is a bit fragile.
 
+20150823:
+	The polarity of Pulse Per Second (PPS) capture events with the
+	uart(4) driver has been corrected.  Prior to this change the PPS
+	"assert" event corresponded to the trailing edge of a positive PPS
+	pulse and the "clear" event was the leading edge of the next pulse.
+	
+	As the width of a PPS pulse in a typical GPS receiver is on the
+	order of 1 millisecond, most users will not notice any significant
+	difference with this change.
+	
+	Anyone who has compensated for the historical polarity reversal by
+	configuring a negative offset equal to the pulse width will need to
+	remove that workaround.
+
 20150822:
 	From legacy ata(4) driver was removed support for SATA controllers
 	supported by more functional drivers ahci(4), siis(4) and mvs(4).