Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
PWMC(4)			 BSD Kernel Interfaces Manual		       PWMC(4)

NAME
     pwmc -- PWM (Pulse	Width Modulation) control device driver

SYNOPSIS
     To	compile	this driver into the kernel, place the following lines in your
     kernel configuration file:

	   device pwmbus
	   device pwmc

     Alternatively, to load the	driver as a module at boot time, place the
     following line in loader.conf(5):

	   pwmc_load="YES"

DESCRIPTION
     The pwmc driver provides device-control access to a channel of PWM	hard-
     ware.  Each instance of a pwmc device is associated with a	single PWM
     output channel.

     Some PWM hardware is organized with multiple channels sharing a common
     clock or other resources.	In such	cases, a separate pwmc 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 hard-
     ware device driver	for details on channels	that share resources.

     An	instance of pwmc creates a character device named /dev/pwm/pwmcX.Y
     where X is	a sequential number assigned to	each PWM hardware controller
     as	it is discovered by the	system,	and Y is the channel number within
     that hardware controller.	The driver can be configured to	create aliases
     that point	to the pwmcX.Y entries,	in effect creating named channels.

     The pwmc driver provides control of a PWM channel with the	following
     ioctl(2) calls and	data structures, defined in <dev/pwm/pwmc.h>:

     PWMGETSTATE (struct pwm_state)
	     Retrieve the current state	of the channel.

     PWMSETSTATE (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 PWMGETSTATE
	     to	get the	current	state and then submit the same data back with
	     just the appropriate value	changed.

     The pwm_state structure is	defined	as follows:

     struct pwm_state {
	     u_int	     period;
	     u_int	     duty;
	     uint32_t	     flags;
	     bool	     enable;
     };

     period  The duration, in nanoseconds, of one complete on-off cycle.

     duty    The duration, in nanoseconds, of the on portion of	one cycle.

     flags   Flags that	affect the output signal can be	bitwise-ORed together.
	     The following flags are currently defined:

	     PWM_POLARITY_INVERTED  Invert the signal polarity.

     enable  False to disable the output signal	or true	to enable it.

HINTS CONFIGURATION
     On	a device.hints(5) based	system,	such as	MIPS, these values are config-
     urable for	pwmc:

     hint.pwmc.%d.at
	     The pwmbus	instance the pwmc instance is attached to.

     hint.pwmc.%d.channel
	     The hardware channel number the instance is attached to.  Channel
	     numbers count up from zero.

     hint.pwmc.%d.label
	     If	this optional hint is set, the driver creates an alias in
	     /dev/pwm with the given name, which points	to the instance.

FDT CONFIGURATION
     On	an fdt(4) based	system,	a pwmc 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 pwmc
     child node	for every channel the hardware supports.  Define only the
     channels you need to control.

     The following properties are required for a pwmc device node:

     compatible
	     Must be the string	"freebsd,pwmc".

     reg     The hardware channel number.

     The following properties are optional for the pwmc	device node:

     label   A string containing only characters legal in a file name.	The
	     driver creates an alias with the given name in /dev/pwm which
	     points to the instance's /dev/pwm/pwmcX.Y device entry.

     Example of	a PWM hardware node containing one pwmc	child node:

     &ehrpwm0 {
	 status	= "okay";
	 pinctrl-names = "default";
	 pinctrl-0 = <&ehrpwm0_AB_pins>;

	 pwmcontrol@0 {
	     compatible	= "freebsd,pwmc";
	     reg = <0>;
	     label = "backlight";
	 };
     };

FILES
     /dev/pwm/pwmc*

SEE ALSO
     fdt(4), device.hints(5), pwm(8), pwm(9)

HISTORY
     The pwmc driver appeared in FreeBSD 13.0.

BSD				 June 17, 2019				   BSD

NAME | SYNOPSIS | DESCRIPTION | HINTS CONFIGURATION | FDT CONFIGURATION | FILES | SEE ALSO | HISTORY

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=pwmc&manpath=FreeBSD+12.1-RELEASE+and+Ports>

home | help