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[bcm283x_pwm] Add documentation for the second PWM channel

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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
This commit is contained in:
Oleksandr Tymoshenko 2018-09-10 22:48:26 +00:00
parent 6c8a899dc5
commit 87acc14608
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=338574
1 changed files with 29 additions and 16 deletions
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45
share/man/man4/man4.arm/bcm283x_pwm.4
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@ -26,7 +26,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd January 22, 2017
.Dd September 10, 2018
.Dt BCM283X_PWM 4
.Os
.Sh NAME
@ -38,43 +38,56 @@
.Sh DESCRIPTION
The
.Nm
driver provides access to the PWM engine on GPIO12 of Rpi 2 and 3 hardware.
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.0.mode"
.It Va dev.pwm.0.mode
.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.
Minmum frequency is 123 kHz, maximum frequency is 125 MHz.
.It Va dev.pwm.0.period
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 frequency will be
In PWM mode, the output frequencies will be
(
.Va dev.pwm.0.freq
/
.Va dev.pwm.0.period .
)
In N/M mode this is the 'M'
.It Va dev.pwm.0.ratio
The "on" period in cycles.
.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 .
In N/M mode this is the 'N'
.It Va dev.pwm.0.pwm_freq
The calculated PWM output frequency in PWM mode.
.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