2. PWM

2. 1 Enabling PWM Interface

• Use luckfox-config to enable the relevant configuration:

1. Open the luckfox-config tool in the terminal:

   sudo luckfox-config

2. Select Interface Options:
   

3. Select PWM:
   

4. Select the PWM interface you want to enable, here we take PWM9 as an example:
   

5. After selecting Enter to confirm, there will be a prompt that UART4 is not available. This is because using the PWM function prevents the simultaneous use of the UART4 interface for serial communication.
   
   

6. View the PWM interface:

   oot@linaro-alip:/home/linaro# ls /sys/class/pwm
   pwmchip0
   root@linaro-alip:/home/linaro# ls -l /sys/class/pwm
   total 0
   lrwxrwxrwx 1 root root 0 6月   6 07:03 pwmchip0 -> ../../devices/platform/fe6f0010.pwm/pwm/pwmchip0

7. The mapping between PWM controllers and register addresses is as follows:

   PWM Controller	Register Address
   pwm8	fe6f0000
   pwm9	fe6f0010
   pwm12	fe700000
   pwm13	fe700010
   pwm14	fe700020
   pwm15	fe700030

2. 2 PWM Control (shell)

1. Ensure that PWM8 has been enabled. The following operations are based on PWM8.

2. You can observe the phenomenon by connecting an LED to the corresponding pin. The opening process is as follows:

   # Export pwm3 to user space
   echo 0 > /sys/class/pwm/pwmchip1/export
   
   # Set PWM period in nanoseconds
   echo 1000000 > /sys/class/pwm/pwmchip1/pwm0/period
   
   # Set duty cycle
   echo 500000 > /sys/class/pwm/pwmchip1/pwm0/duty_cycle
   
   # Set PWM polarity
   echo "normal" > /sys/class/pwm/pwmchip1/pwm0/polarity
   
   # Enable PWM
   echo 1 > /sys/class/pwm/pwmchip1/pwm0/enable
   
   # Unexport pwm3 from user space
   echo 0 > /sys/class/pwm/pwmchip1/unexport

2. 3 Controlling PWM Using python-periphery

1. Ensure that PWM8 has been enabled. The following operations are based on PWM8.

2. The sample code for PWM output using the python-periphery library is as follows:

   from periphery import PWM
   import time
   import numpy as np
   
   # Open PWM chip 0, channel 0 pwm = PWM(0, 0)
   pwm = PWM(0, 0)
   
   # Set frequency to 100 Hz
   pwm.frequency = 1e2
   
   #set the PWM’s output polarity
   pwm.polarity = "normal"
   
   # Set duty cycle to 0
   pwm.duty_cycle = 0
   
   pwm.enable()
   
   # Change duty cycle 
   for i in np.arange(0.0, 1.0, 0.05):
       pwm.duty_cycle = i
       time.sleep(1)
   
   pwm.close()

3. Run the program, and you will see the LED connected to Pin 33 gradually brighten.