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+.\"
+.\" Copyright (c) 2015 Ian Lepore <ian@freebsd.org>
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\"
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd August 12, 2015
+.Dt AM335X_DMTPPS 4
+.Os
+.Sh NAME
+.Nm am335x_dmtpps
+.Nd RFC 2783 Pulse Per Second API driver for AM335x systems
+.Sh SYNOPSIS
+.Cd "device am335x_dmtpps"
+.Pp
+Optional in
+.Pa /boot/loader.conf :
+.Cd hw.am335x_dmtpps.input="pin name"
+.\"
+.Sh DESCRIPTION
+The
+.Nm
+device driver provides a system time counter that includes precise
+capture of Pulse Per Second (PPS) signals emitted by GPS receivers
+and other timing devices.
+The
+.Nm
+driver may be compiled into the kernel or loaded as a module.
+.Pp
+The AM335x timer hardware captures the value of the system time counter
+on the leading edge of the PPS pulse.
+Because the capture is done by the hardware there is no interrupt
+latency in the measurement.
+The time counter runs at 24Mhz, providing a measurement resolution
+of 42 nanoseconds.
+.Pp
+To use the PPS timing information provided by this driver with
+.Xr ntpd 8 ,
+symlink the
+.Pa /dev/dmtpps
+device to
+.Pa /dev/pps0
+and configure server
+.Va 127.127.22.0
+in
+.Xr ntp.conf 5
+to configure a type 22 (ATOM) refclock.
+.\"
+.Sh DRIVER CONFIGURATION
+The AM335x hardware provides four timer devices with a capture input
+pin, DMTimer4 through DMTimer7.
+Because it also provides the active system time counter,
+only one instance of the
+.Nm
+driver can be active at a time.
+The driver uses system pin configuration to determine which hardware
+timer device to use.
+Configure the timer input pin in the system's FDT data, or by
+supplying the pin name using a tunable variable in
+.Xr loader.conf 5 .
+.Pp
+To use a standard kernel and FDT data, use
+.Xr loader.conf 5
+to load the
+.Nm
+module and set the
+.Va hw.am335x_dmtpps.input
+tunable variable to the name of the input pin, one of the following:
+.Pp
+.Bl -tag -width "GPMC_ADVn_ALE MMMM" -offset MMMM -compact
+.It Em Name
+.Em Hardware
+.It P8-7
+DMTimer4; Beaglebone P8 header pin 7.
+.It P8-8
+DMTimer7; Beaglebone P8 header pin 8.
+.It P8-9
+DMTimer5; Beaglebone P8 header pin 9.
+.It P8-10
+DMTimer6; Beaglebone P8 header pin 10.
+.It GPMC_ADVn_ALE
+DMTimer4.
+.It GPMC_BEn0_CLE
+DMTimer5.
+.It GPMC_WEn
+DMTimer6.
+.It GPMC_OEn_REn
+DMTimer7.
+.El
+.Pp
+To configure the
+.Nm
+driver using FDT data, create a new pinctrl node by referencing the standard
+.Va am33xx_pinmux
+driver node (which is defined in am33xx.dtsi) in your dts file.
+For example:
+.Bd -literal
+   &am33xx_pinmux {
+      timer4_pins: timer4_pins {
+         pinctrl-single,pins = <0x90 (PIN_INPUT | MUX_MODE2)>;
+      };
+   };
+.Ed
+.Pp
+Add pinctrl properties referencing
+.Va timer4_pins
+to the standard
+.Va timer4
+device node (also defined in am33xx.dtsi) by referencing it in
+your dts file as follows:
+.Bd -literal
+   &timer4 {
+      pinctrl-names = "default";
+      pinctrl-0 = <&timer4_pins>;
+   };
+.Ed
+.\"
+.Sh FILES
+.Bl -tag -width ".Pa /dev/dmtpps" -compact
+.It Pa /dev/dmtpps
+The device providing
+.Xr ioctl 2
+access to the RFC 2783 API.
+.El
+.\"
+.Sh SEE ALSO
+.Xr timecounters 4 ,
+.Xr loader.conf 5 ,
+.Xr ntp.conf 5 ,
+.Xr ntpd 8
+.\"
+.Sh HISTORY
+The
+.Nm
+device driver first appeared in
+.Fx 11.0 .
+.\"
+.Sh AUTHORS
+The
+.Nm
+device driver and this manual page were written by
+.An Ian Lepore Aq Mt ian@FreeBSD.org .