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.

The historical UART_PPS_ON_CTS kernel option is still honored, but now it
can be overridden at runtime using a tunable to configure all uart devices
(hw.uart.pps_mode) or specific devices (dev.uart.#.pps_mode).  The per-
device config is both a tunable and a writable sysctl.

This syncs the PPS capabilities of uart(4) with the enhancements recently
recently added to ucom(4) for capturing from USB serial devices.

Relnotes:	yes

1 files changed, 34 insertions, 1 deletions

diff --git a/share/man/man4/uart.4 b/share/man/man4/uart.4
index 748d6cb..3fca2f8 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?