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.\" Copyright (c) 2017 Poul-Henning Kamp <phk@FreeBSD.org>
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.Dd September 10, 2018
.Dt BCM283X_PWM 4
.Os
.Sh NAME
.Nm bcm283x_pwm
.Nd bcm283x_pwm - driver for Raspberry Pi 2/3 PWM
.Sh SYNOPSIS
.Cd "kldload bcm283x_clkman"
.Cd "kldload bcm283x_pwm"
.Sh DESCRIPTION
The
.Nm
driver provides access to the PWM engine on GPIO12 of Raspberry Pi 2 and 3 hardware.
.Pp
The PWM hardware is controlled via the
.Xr sysctl 8
interface:
.Bd -literal
dev.pwm.0.mode: 1
dev.pwm.0.mode2: 1
dev.pwm.0.freq: 125000000
dev.pwm.0.ratio: 2500
dev.pwm.0.ratio2: 2500
dev.pwm.0.period: 10000
dev.pwm.0.period2: 10000
dev.pwm.0.pwm_freq: 12500
dev.pwm.0.pwm_freq2: 12500
.Ed
.Bl -tag -width ".Va dev.pwm"
.It Va dev.pwm.0.mode , dev.pwm.0.mode2
PWM Mode for channels 1 and 2.
Three modes exist, 0=off, 1=PWM, 2=N/M.
The N/M mode is a first order delta-sigma mode, which makes a quite
handy DAC output with a trivial RC lowpass filter.
.Pp
.It Va dev.pwm.0.freq
The input frequency to the PWM hardware in Hz.
Applies to both channels 1 and 2.
Minimum frequency is 123 kHz, maximum frequency is 125 MHz.
.It Va dev.pwm.0.period , dev.pwm.0.period2
The period length in cycles.
In PWM mode, the output frequencies will be
(
.Va dev.pwm.0.freq
/
.Va dev.pwm.period
) and (
.Va dev.pwm.0.freq2
/
.Va dev.pwm.0.period2
).
In N/M mode this is the 'M'.
.It Va dev.pwm.0.ratio , dev.pwm.0.ratio2
The "on" period in cycles for PWM channels 1 and 2.
In PWM mode, to get a 25% dutycycle, set this to 25% of
.Va dev.pwm.0.period
or
.Va dev.pwm.0.period2 ,
as appropriate.
In N/M mode this is the 'N'.
.It Va dev.pwm.0.pwm_freq , dev.pwm.0.pwm_freq2
The calculated PWM output frequencies in PWM mode, for channels 1 and 2.
.El
.Pp
.Sh NOTES
Currently the
.Nm
driver ignores the 'status="disabled"' flag in the DTB, assuming that
if you load the driver, you want it to work.
.Sh SEE ALSO
.Xr sysctl 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 12.0 .
.Sh AUTHORS
.An -nosplit
The
.Nm
driver and this manual page were written by
.An Poul-Henning Kamp Aq Mt phk@FreeBSD.org .