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2.\" Copyright (c) 2015 Ian Lepore <ian@freebsd.org>
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26.Dd August 12, 2015
27.Dt AM335X_DMTPPS 4
28.Os
29.Sh NAME
30.Nm am335x_dmtpps
31.Nd RFC 2783 Pulse Per Second API driver for AM335x systems
32.Sh SYNOPSIS
33.Cd "device am335x_dmtpps"
34.Pp
35Optional in
36.Pa /boot/loader.conf :
37.Cd hw.am335x_dmtpps.input="pin name"
38.\"
39.Sh DESCRIPTION
40The
41.Nm
42device driver provides a system time counter that includes precise
43capture of Pulse Per Second (PPS) signals emitted by GPS receivers
44and other timing devices.
45The
46.Nm
47driver may be compiled into the kernel or loaded as a module.
48.Pp
49The AM335x timer hardware captures the value of the system time counter
50on the leading edge of the PPS pulse.
51Because the capture is done by the hardware there is no interrupt
52latency in the measurement.
53The time counter runs at 24Mhz, providing a measurement resolution
54of 42 nanoseconds.
55.Pp
56To use the PPS timing information provided by this driver with
57.Xr ntpd 8 ,
58symlink the
59.Pa /dev/dmtpps
60device to
61.Pa /dev/pps0
62and configure server
63.Va 127.127.22.0
64in
65.Xr ntp.conf 5
66to configure a type 22 (ATOM) refclock.
67.\"
68.Sh DRIVER CONFIGURATION
69The AM335x hardware provides four timer devices with a capture input
70pin, DMTimer4 through DMTimer7.
71Because it also provides the active system time counter,
72only one instance of the
73.Nm
74driver can be active at a time.
75The driver uses system pin configuration to determine which hardware
76timer device to use.
77Configure the timer input pin in the system's FDT data, or by
78supplying the pin name using a tunable variable in
79.Xr loader.conf 5 .
80.Pp
81To use a standard kernel and FDT data, use
82.Xr loader.conf 5
83to load the
84.Nm
85module and set the
86.Va hw.am335x_dmtpps.input
87tunable variable to the name of the input pin, one of the following:
88.Pp
89.Bl -tag -width "GPMC_ADVn_ALE MMMM" -offset MMMM -compact
90.It Em Name
91.Em Hardware
92.It P8-7
93DMTimer4; Beaglebone P8 header pin 7.
94.It P8-8
95DMTimer7; Beaglebone P8 header pin 8.
96.It P8-9
97DMTimer5; Beaglebone P8 header pin 9.
98.It P8-10
99DMTimer6; Beaglebone P8 header pin 10.
100.It GPMC_ADVn_ALE
101DMTimer4.
102.It GPMC_BEn0_CLE
103DMTimer5.
104.It GPMC_WEn
105DMTimer6.
106.It GPMC_OEn_REn
107DMTimer7.
108.El
109.Pp
110To configure the
111.Nm
112driver using FDT data, create a new pinctrl node by referencing the standard
113.Va am33xx_pinmux
114driver node (which is defined in am33xx.dtsi) in your dts file.
115For example:
116.Bd -literal
117   &am33xx_pinmux {
118      timer4_pins: timer4_pins {
119         pinctrl-single,pins = <0x90 (PIN_INPUT | MUX_MODE2)>;
120      };
121   };
122.Ed
123.Pp
124Add pinctrl properties referencing
125.Va timer4_pins
126to the standard
127.Va timer4
128device node (also defined in am33xx.dtsi) by referencing it in
129your dts file as follows:
130.Bd -literal
131   &timer4 {
132      pinctrl-names = "default";
133      pinctrl-0 = <&timer4_pins>;
134   };
135.Ed
136.\"
137.Sh FILES
138.Bl -tag -width ".Pa /dev/dmtpps" -compact
139.It Pa /dev/dmtpps
140The device providing
141.Xr ioctl 2
142access to the RFC 2783 API.
143.El
144.\"
145.Sh SEE ALSO
146.Xr timecounters 4 ,
147.Xr loader.conf 5 ,
148.Xr ntp.conf 5 ,
149.Xr ntpd 8
150.\"
151.Sh HISTORY
152The
153.Nm
154device driver first appeared in
155.Fx 11.0 .
156.\"
157.Sh AUTHORS
158The
159.Nm
160device driver and this manual page were written by
161.An Ian Lepore Aq Mt ian@FreeBSD.org .
162