PWM Configuration

1. Under the root directory of freelight-u-sdk, run the following command to enter the kernel menu configuration GUI.

   make linux-menuconfig

2. Enter the Device Drivers menu.

3. Enter the PWM support menu.

4. Select the StarFive PWM PTC Support option.

5. Save your change and exit the kernel configuration dialog.

The following code example (in the jh7110-common.dtsi file) defines two PWM output pins for the system. It sets up which pin to use, what function the pin has, input/output settings, and how the PWM signal is controlled.

pwm_pins: pwm-pins {
                pwm_ch0-pins {
                        sf,pins = <PAD_GPIO46>;
                        sf,pinmux = <PAD_GPIO46_FUNC_SEL 0>;
                        sf,pin-ioconfig = <IO(GPIO_IE(1))>;
                        sf,pin-gpio-dout = <GPO_PTC0_PWM_0>;
                        sf,pin-gpio-doen = <OEN_PTC0_PWM_0_OE_N>;
                };

                pwm_ch1-pins {
                        sf,pins = <PAD_GPIO59>;
                        sf,pinmux = <PAD_GPIO59_FUNC_SEL 0>;
                        sf,pin-ioconfig = <IO(GPIO_IE(1))>;
                        sf,pin-gpio-dout = <GPO_PTC0_PWM_1>;
                        sf,pin-gpio-doen = <OEN_PTC0_PWM_1_OE_N>;
                };
};

For PWM Channel 0 (GPIO46):

• sf,pins = <PAD_GPIO46>;: Use physical pin GPIO46.
• sf,pinmux = <PAD_GPIO46_FUNC_SEL 0>;: Function 0 = PWM output
• sf,pin-ioconfig = <IO(GPIO_IE(1))>;: Enables input.
• sf,pin-gpio-dout = <GPO_PTC0_PWM_0>;: Connects the pin to PWM channel 0 output.
• sf,pin-gpio-doen = <OEN_PTC0_PWM_0_OE_N>;: Enables output for PWM channel 0.

For PWM Channel 1 (GPIO59):

• sf,pins = <PAD_GPIO59>;: Uses physical pin GPIO59.
• sf,pinmux = <PAD_GPIO59_FUNC_SEL 0>;: Function 0 = PWM output
• sf,pin-ioconfig = <IO(GPIO_IE(1))>;: Enables input.
• sf,pin-gpio-dout = <GPO_PTC0_PWM_1>;: Connects to PWM channel 1 output
• sf,pin-gpio-doen = <OEN_PTC0_PWM_1_OE_N>;: Enables output control for PWM channel 1

1. Run the following command to list all registeredd PWM chips.

   # cd /sys/class/pwm/
   # ls
   

2. Enter the directory pwmchip* and run the following command:

    echo X > export

   where X is the PWM channel that you want to configure.
   The command generates the pwmX directory as follows:

   # cd pwmchip0/
   # ls
   device     export     npwm       power      subsystem  uevent     unex-port
   # echo 0 > export
   # ls
   device     npwm       pwm0       uevent
   export     power      subsystem  unexport
   # echo 1 > export
   # ls
   device     npwm       pwm0       subsystem  unexport
   export     power      pwm1       uevent

3. Enter the directory pwmX, edit the target variables of the PWM channel.

   # cd pwm0/
   # ls
   capture     enable      polarity    uevent
   duty_cycle  period      power
   # echo 10000 > period
   # echo 5000 > duty_cycle 
   # cat period 
   10000
   # cat duty_cycle 
   5000
   # cat polarity 
   normal
   # cat enable 
   1

   • enable: Enables or disables the channel. 1 for enable, and 0 for disable.
   • polarity: Whether to invert polarity. 1 to invert polarity and 0 not to invert (normal)
   • period: Specifies the period of the PWM signal in unit of ns.
   • duty_cycle: Specifies the duty cycle of the PWM signal in unit of ns.