1.\"
2.\" Copyright (c) 2015 Ian Lepore <ian@freebsd.org>
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26.\" $FreeBSD$
27.\"
28.Dd August 12, 2015
29.Dt AM335X_DMTPPS 4
30.Os
31.Sh NAME
32.Nm am335x_dmtpps
33.Nd RFC 2783 Pulse Per Second API driver for AM335x systems
34.Sh SYNOPSIS
35.Cd "device am335x_dmtpps"
36.Pp
37Optional in
38.Pa /boot/loader.conf :
39.Cd hw.am335x_dmtpps.input="pin name"
40.\"
41.Sh DESCRIPTION
42The
43.Nm
44device driver provides a system time counter that includes precise
45capture of Pulse Per Second (PPS) signals emitted by GPS receivers
46and other timing devices.
47The
48.Nm
49driver may be compiled into the kernel or loaded as a module.
50.Pp
51The AM335x timer hardware captures the value of the system time counter
52on the leading edge of the PPS pulse.
53Because the capture is done by the hardware there is no interrupt
54latency in the measurement.
55The time counter runs at 24Mhz, providing a measurement resolution
56of 42 nanoseconds.
57.Pp
58To use the PPS timing information provided by this driver with
59.Xr ntpd 8 ,
60symlink the
61.Pa /dev/dmtpps
62device to
63.Pa /dev/pps0
64and configure server
65.Va 127.127.22.0
66in
67.Xr ntp.conf 5
68to configure a type 22 (ATOM) refclock.
69.\"
70.Sh DRIVER CONFIGURATION
71The AM335x hardware provides four timer devices with a capture input
72pin, DMTimer4 through DMTimer7.
73Because it also provides the active system time counter,
74only one instance of the
75.Nm
76driver can be active at a time.
77The driver uses system pin configuration to determine which hardware
78timer device to use.
79Configure the timer input pin in the system's FDT data, or by
80supplying the pin name using a tunable variable in
81.Xr loader.conf 5 .
82.Pp
83To use a standard kernel and FDT data, use
84.Xr loader.conf 5
85to load the
86.Nm
87module and set the
88.Va hw.am335x_dmtpps.input
89tunable variable to the name of the input pin, one of the following:
90.Pp
91.Bl -tag -width "GPMC_ADVn_ALE MMMM" -offset MMMM -compact
92.It Em Name
93.Em Hardware
94.It P8-7
95DMTimer4; Beaglebone P8 header pin 7.
96.It P8-8
97DMTimer7; Beaglebone P8 header pin 8.
98.It P8-9
99DMTimer5; Beaglebone P8 header pin 9.
100.It P8-10
101DMTimer6; Beaglebone P8 header pin 10.
102.It GPMC_ADVn_ALE
103DMTimer4.
104.It GPMC_BEn0_CLE
105DMTimer5.
106.It GPMC_WEn
107DMTimer6.
108.It GPMC_OEn_REn
109DMTimer7.
110.El
111.Pp
112To configure the
113.Nm
114driver using FDT data, create a new pinctrl node by referencing the standard
115.Va am33xx_pinmux
116driver node (which is defined in am33xx.dtsi) in your dts file.
117For example:
118.Bd -literal
119   &am33xx_pinmux {
120      timer4_pins: timer4_pins {
121         pinctrl-single,pins = <0x90 (PIN_INPUT | MUX_MODE2)>;
122      };
123   };
124.Ed
125.Pp
126Add pinctrl properties referencing
127.Va timer4_pins
128to the standard
129.Va timer4
130device node (also defined in am33xx.dtsi) by referencing it in
131your dts file as follows:
132.Bd -literal
133   &timer4 {
134      pinctrl-names = "default";
135      pinctrl-0 = <&timer4_pins>;
136   };
137.Ed
138.\"
139.Sh FILES
140.Bl -tag -width ".Pa /dev/dmtpps" -compact
141.It Pa /dev/dmtpps
142The device providing
143.Xr ioctl 2
144access to the RFC 2783 API.
145.El
146.\"
147.Sh SEE ALSO
148.Xr timecounters 4 ,
149.Xr loader.conf 5 ,
150.Xr ntp.conf 5 ,
151.Xr ntpd 8
152.\"
153.Sh HISTORY
154The
155.Nm
156device driver first appeared in
157.Fx 11.0 .
158.\"
159.Sh AUTHORS
160The
161.Nm
162device driver and this manual page were written by
163.An Ian Lepore Aq Mt ian@FreeBSD.org .
164