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, 34 insertions, 1 deletions

diff --git a/share/man/man4/uart.4 b/share/man/man4/uart.4
index 644c37d..d520409 100644
--- a/share/man/man4/uart.4
+++ b/share/man/man4/uart.4
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 12, 2008
+.Dd August 10, 2015
 .Dt UART 4
 .Os
 .Sh NAME
@@ -151,6 +151,39 @@ SCC: serial communications controllers supported by the
 device driver.
 .El
 .\"
+.Sh Pulse Per Second (PPS) Timing Interface
+The
+.Nm
+driver can capture PPS timing information as defined in RFC 2783.
+The API, accessed via
+.Xr ioctl 8 ,
+is available on the tty device.
+To use the PPS capture feature with
+.Xr ntpd 8 ,
+symlink the tty device to
+.Va /dev/pps0.
+.Pp
+The
+.Va hw.uart.pps_mode
+tunable configures the PPS capture mode for all uart devices;
+it can be set in
+.Xr loader.conf 5 .
+The
+.Va dev.uart.0.pps_mode
+sysctl configures the PPS capture mode for a specific uart device;
+it can be set in
+.Xr loader.conf 5
+or
+.Xr sysctl.conf 5 .
+The following capture modes are available:
+.Bl -tag -compact -offset "mmmm" -width "mmmm"
+.It 0
+Capture disabled.
+.It 1
+Capture pulses on the CTS line.
+.It 2
+Capture pulses on the DCD line (default).
+.El
 .Sh FILES
 .Bl -tag -width ".Pa /dev/ttyu?.init" -compact
 .It Pa /dev/ttyu?