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