Add a pwmc(4) manpage.
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Ian Lepore
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0309916a88
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@ -418,6 +418,7 @@ MAN= aac.4 \
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pts.4 \
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pty.4 \
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puc.4 \
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pwmc.4 \
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${_qlxge.4} \
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${_qlxgb.4} \
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${_qlxgbe.4} \
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212
share/man/man4/pwmc.4
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212
share/man/man4/pwmc.4
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@ -0,0 +1,212 @@
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.\"
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.\" Copyright (c) 2019 Ian Lepore <ian@freebsd.org>
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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 June 17, 2019
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.Dt PWMC 4
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.Os
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.Sh NAME
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.Nm pwmc
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.Nd PWM (Pulse Width Modulation) control device driver
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.Sh SYNOPSIS
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To compile this driver into the kernel,
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place the following lines in your
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kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "device pwmbus"
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.Cd "device pwmc"
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.Ed
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.Pp
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Alternatively, to load the driver as a
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module at boot time, place the following line in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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pwmc_load="YES"
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.Ed
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.Sh DESCRIPTION
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The
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.Nm
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driver provides device-control access to a channel of PWM hardware.
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Each instance of a
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.Nm
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device is associated with a single PWM output channel.
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.Pp
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Some PWM hardware is organized with multiple channels sharing a
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common clock or other resources.
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In such cases, a separate
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.Nm
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instance will exist for each channel, but changing the period or
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duty cycle of any one channel may affect other channels within the
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hardware which share the same resources.
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Consult the documentation for the underlying PWM hardware device driver
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for details on channels that share resources.
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.Pp
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An instance of
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.Nm
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creates a character device named
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.Pa /dev/pwm/pwmcX.Y
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where
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.Va X
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is a sequential number assigned to each PWM hardware controller
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as it is discovered by the system, and
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.Va Y
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is the channel number within that hardware controller.
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The driver can be configured to create aliases that point to the
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.Pa pwmcX.Y
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entries, in effect creating named channels.
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.Pp
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The
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.Nm
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driver provides control of a PWM channel with the following
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.Xr ioctl 2
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calls and data structures, defined in
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.In dev/pwm/pwmc.h :
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.Bl -tag -width indent
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.It Dv PWMGETSTATE Pq Vt "struct pwm_state"
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Retrieve the current state of the channel.
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.It Dv PWMSETSTATE Pq Vt "struct pwm_state"
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Set the current state of the channel.
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All parameters are updated on every call.
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To change just one of the values, use
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.Dv PWMGETSTATE
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to get the current state and then submit the same data back with
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just the appropriate value changed.
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.El
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.Pp
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The
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.Va pwm_state
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structure is defined as follows:
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.Bd -literal
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struct pwm_state {
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u_int period;
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u_int duty;
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uint32_t flags;
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bool enable;
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};
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.Ed
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.Pp
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.Bl -tag -width period
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.It Va period
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The duration, in nanoseconds, of one complete on-off cycle.
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.It Va duty
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The duration, in nanoseconds, of the on portion of one cycle.
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.It Va flags
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Flags that affect the output signal can be bitwise-ORed together.
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The following flags are currently defined:
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.Pp
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.Bl -tag -width PWM_POLARITY_INVERTED -compact
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.It Dv PWM_POLARITY_INVERTED
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Invert the signal polarity.
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.El
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.It Va enable
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.Va
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False to disable the output signal or true to enable it.
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.El
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.Sh HINTS CONFIGURATION
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On a
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.Xr device.hints 5
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based system, such as
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.Li MIPS ,
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these values are configurable for
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.Nm :
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.Bl -tag -width indent
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.It Va hint.pwmc.%d.at
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The pwmbus instance the
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.Nm
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instance is attached to.
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.It Va hint.pwmc.%d.channel
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The hardware channel number the instance is attached to.
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Channel numbers count up from zero.
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.It Va hint.pwmc.%d.label
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If this optional hint is set, the driver creates an alias in
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.Pa /dev/pwm
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with the given name, which points to the instance.
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.El
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.Sh FDT CONFIGURATION
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On an
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.Xr fdt 4
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based system, a
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.Nm
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device is described with a child node of the pwm hardware controller node.
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When the hardware supports multiple channels within the controller, it is
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not necessary to include a
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.Nm
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child node for every channel the hardware supports.
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Define only the channels you need to control.
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.Pp
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The following properties are required for a
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.Nm
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device node:
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.Bl -tag -width indent
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.It Va compatible
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Must be the string "freebsd,pwmc".
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.It Va reg
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The hardware channel number.
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.El
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.Pp
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The following properties are optional for the
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.Nm
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device node:
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.Bl -tag -width indent
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.It Va label
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A string containing only characters legal in a file name.
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The driver creates an alias with the given name in
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.Pa /dev/pwm
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which points to the instance's
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.Pa /dev/pwm/pwmcX.Y
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device entry.
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.El
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.Pp
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Example of a PWM hardware node containing one
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.Nm
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child node:
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.Bd -literal
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&ehrpwm0 {
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status = "okay";
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pinctrl-names = "default";
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pinctrl-0 = <&ehrpwm0_AB_pins>;
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pwmcontrol@0 {
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compatible = "freebsd,pwmc";
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reg = <0>;
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label = "backlight";
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};
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};
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.Ed
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.Sh FILES
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.Bl -tag -width -compact
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.It Pa /dev/pwm/pwmc*
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.El
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.Sh SEE ALSO
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.Xr fdt 4 ,
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.Xr device.hints 5 ,
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.Xr pwm 8 ,
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.Xr pwm 9
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.Sh HISTORY
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The
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.Nm
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driver
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appeared in
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.Fx 13.0 .
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