man/man4/pwmc.4

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

    pwmcontrol@0 {
        compatible = "freebsd,pwmc";
        reg = <0>;
        label = "backlight";
    };
};
.Ed
.Sh FILES
.Bl -tag -width -compact
.It Pa /dev/pwm/pwmc*
.El
.Sh SEE ALSO
.Xr fdt 4 ,
.Xr device.hints 5 ,
.Xr pwm 8 ,
.Xr pwm 9
.Sh HISTORY
The
.Nm
driver
appeared in
.Fx 13.0 .