[bcm283x_pwm] Add documentation for the second PWM channel
Document sysctls for the second PWM channel added in r335855 Also fix some minor style issues and a typo. Approved by: re (gjb) Submitted by: bobf@mrp3.com Reviewed by: 0mp Differential Revision: https://reviews.freebsd.org/D17084
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2020-12-20 02:59:44 +00:00
svn path=/head/; revision=338574
@ -26,7 +26,7 @@
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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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.Dd September 10, 2018
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.Dt BCM283X_PWM 4
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.Os
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.Sh NAME
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@ -38,43 +38,56 @@
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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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driver provides access to the PWM engine on GPIO12 of Raspberry Pi 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.mode2: 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.ratio2: 2500
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dev.pwm.0.period: 10000
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dev.pwm.0.period2: 10000
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dev.pwm.0.pwm_freq: 12500
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dev.pwm.0.pwm_freq2: 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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.Bl -tag -width ".Va dev.pwm"
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.It Va dev.pwm.0.mode , dev.pwm.0.mode2
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PWM Mode for channels 1 and 2.
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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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Applies to both channels 1 and 2.
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Minimum frequency is 123 kHz, maximum frequency is 125 MHz.
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.It Va dev.pwm.0.period , dev.pwm.0.period2
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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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In PWM mode, the output frequencies 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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.Va dev.pwm.period
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) and (
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.Va dev.pwm.0.freq2
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/
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.Va dev.pwm.0.period2
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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 , dev.pwm.0.ratio2
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The "on" period in cycles for PWM channels 1 and 2.
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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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.Va dev.pwm.0.period
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or
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.Va dev.pwm.0.period2 ,
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as appropriate.
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In N/M mode this is the 'N'.
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.It Va dev.pwm.0.pwm_freq , dev.pwm.0.pwm_freq2
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The calculated PWM output frequencies in PWM mode, for channels 1 and 2.
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.El
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.Pp
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.Sh NOTES
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