98 lines
3.0 KiB
Groff
98 lines
3.0 KiB
Groff
.\"
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.\" SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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.\"
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.\" Copyright (c) 2017 Poul-Henning Kamp <phk@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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.\" 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 January 22, 2017
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.Dt BCM283X_PWM 4
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.Os
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.Sh NAME
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.Nm bcm283x_pwm
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.Nd bcm283x_pwm - driver for Raspberry Pi 2/3 PWM
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.Sh SYNOPSIS
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.Cd "kldload bcm283x_clkman"
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.Cd "kldload bcm283x_pwm"
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.Sh DESCRIPTION
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The
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.Nm
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driver provides access to the PWM engine on GPIO12 of Rpi 2 and 3 hardware.
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.Pp
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The PWM hardware is controlled via the
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.Xr sysctl 8
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interface:
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.Bd -literal
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dev.pwm.0.mode: 1
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dev.pwm.0.freq: 125000000
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dev.pwm.0.ratio: 2500
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dev.pwm.0.period: 10000
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dev.pwm.0.pwm_freq: 12500
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.Ed
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.Bl -tag -width ".Va dev.pwm.0.mode"
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.It Va dev.pwm.0.mode
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Three modes exist, 0=off, 1=PWM, 2=N/M.
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The N/M mode is a first order delta-sigma mode, which makes a quite
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handy DAC output with a trivial RC lowpass filter.
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.Pp
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.It Va dev.pwm.0.freq
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The input frequency to the PWM hardware in Hz.
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Minmum frequency is 123 kHz, maximum frequency is 125 MHz.
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.It Va dev.pwm.0.period
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The period length in cycles.
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In PWM mode, the output frequency will be
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(
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.Va dev.pwm.0.freq
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/
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.Va dev.pwm.0.period .
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)
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In N/M mode this is the 'M'
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.It Va dev.pwm.0.ratio
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The "on" period in cycles.
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In PWM mode, to get a 25% dutycycle, set this to 25% of
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.Va dev.pwm.0.period .
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In N/M mode this is the 'N'
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.It Va dev.pwm.0.pwm_freq
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The calculated PWM output frequency in PWM mode.
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.El
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.Pp
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.Sh NOTES
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Currently the
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.Nm
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driver ignores the 'status="disabled"' flag in the DTB, assuming that
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if you load the driver, you want it to work.
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.Sh SEE ALSO
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.Xr sysctl 8
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.Sh HISTORY
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The
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.Nm
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driver first appeared in
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.Fx 12.0 .
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.Sh AUTHORS
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.An -nosplit
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The
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.Nm
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driver and this manual page were written by
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.An Poul-Henning Kamp Aq Mt phk@FreeBSD.org .
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