PWMC(4)                FreeBSD 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
     hardware.  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
     hardware 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
     configurable 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.

FreeBSD 13.1-RELEASE-p6          June 17, 2019         FreeBSD 13.1-RELEASE-p6