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.