流程概要

• 配置

  • 在＂/boot/firmware/config.txt＂中添加＂dtoverlay=pwm＂。
    重启，会激活＂GPIO18＂——＂PWM0_CHAN2＂

• 使用

  • BASH
    于＂/sys/class/pwm/class/pwmchip0＂，

    echo 2 > export
    cd pwm2
    
    echo 1000000 > period #可配置，周期
    echo 500000 > duty_cycle #可配置，占空比
    echo 1 > enable #开始
    #echo normal > polarity #可配置，极性，默认normal
    
    echo 0 > enable #停止
    cd .. #回到pwmchip0
    echo 2 > unexport
    

  • lua-peripheral

    local PWM = Periphery.PWM
    local PWM_Chip_Channel=PWM(0,2)
    --  PWM_CHIP, PWM_CHANNEL
    PWM_Chip_Channel.frequency = 1000000
    PWM_Chip_Channel.duty_cycle = 0.5
    PWM_Chip_Channel:enable()
    --
    PWM_Chip_Channel:disable()
      PWM_Chip_Channel:close()
    

详情

• 环境：
  • 内核版本=6.18.33+rpt-rpi-2712
  • 系统版本=Debian GNU/Linux 13 (trixie)
• 关于＂/boot/firmware/config.txt＂的配置，
  见＂/boot/firmware/overlays/README＂，
  包含：pwm、pwm-2chan、pwm-gpio等。
• lua-periphery参考：vsergeev/lua-periphery: A Lua library for peripheral I/O (GPIO, LED, PWM, SPI, I2C, MMIO, Serial) in Linux.

扩展

• 摘录＂/boot/firmware/overlays/README＂中＂pwm＂部分：

Name:   pwm
Info:   Configures a single PWM channel
        Legal pin,function combinations for each channel:
          PWM0: 12,4(Alt0) 18,2(Alt5) 40,4(Alt0)            52,5(Alt1)
          PWM1: 13,4(Alt0) 19,2(Alt5) 41,4(Alt0) 45,4(Alt0) 53,5(Alt1)
        N.B.:
          1) Pin 18 is the only one available on all platforms, and
             it is the one used by the I2S audio interface.
             Pins 12 and 13 might be better choices on an A+, B+ or Pi2.
          2) The onboard analogue audio output uses both PWM channels.
          3) So be careful mixing audio and PWM.
          4) Currently the clock must have been enabled and configured
             by other means.
Load:   dtoverlay=pwm,<param>=<val>
Params: pin                     Output pin (default 18) - see table
        func                    Pin function (default 2 = Alt5) - see above
        clock                   PWM clock frequency (informational)

Name:   pwm-2chan
Info:   Configures both PWM channels
        Legal pin,function combinations for each channel:
          PWM0: 12,4(Alt0) 18,2(Alt5) 40,4(Alt0)            52,5(Alt1)
          PWM1: 13,4(Alt0) 19,2(Alt5) 41,4(Alt0) 45,4(Alt0) 53,5(Alt1)
        N.B.:
          1) Pin 18 is the only one available on all platforms, and
             it is the one used by the I2S audio interface.
             Pins 12 and 13 might be better choices on an A+, B+ or Pi2.
          2) The onboard analogue audio output uses both PWM channels.
          3) So be careful mixing audio and PWM.
          4) Currently the clock must have been enabled and configured
             by other means.
Load:   dtoverlay=pwm-2chan,<param>=<val>
Params: pin                     Output pin (default 18) - see table
        pin2                    Output pin for other channel (default 19)
        func                    Pin function (default 2 = Alt5) - see above
        func2                   Function for pin2 (default 2 = Alt5)
        clock                   PWM clock frequency (informational)

Name:   pwm-gpio
Info:   Configures the software PWM GPIO driver
Load:   dtoverlay=pwm-gpio,<param>=<val>
Params: gpio                    Output pin (default 4)

• ＂/sys/class/pwm/pwmchip0/＂为逻辑路径，

  • 当配置，在＂/boot/firmware/config.txt＂中添加＂dtoverlay=pwm＂后时，其链接到＂/sys/devices/platform/axi/1000120000.pcie/1f00098000.pwm/pwm/pwmchip0/＂（对应以上cat /sys/kernel/debug/pwm中的＂1: platform/1f00098000.pwm＂）；
  • 当未配置时，其链接到＂/sys/devices/platform/axi/1000120000.pcie/1f0009c000.pwm/pwm/pwmchip0/＂（对应以上cat /sys/kernel/debug/pwm中的＂1: platform/1f0009c000.pwm＂）。

  故，不可依赖路径名称＂pwmchip0＂。

• cat /sys/kernel/debug/pwm可以查看所有pwm的配置，如

  0: platform/1f00098000.pwm, npwm: 4
   pwm-0   ((null)              ):
  	requested configuration: disabled, 0/0 ns, normal polarity
  	actual configuration:    disabled, 0/0 ns, normal polarity
   pwm-1   ((null)              ):
  	requested configuration: disabled, 0/0 ns, normal polarity
  	actual configuration:    disabled, 0/0 ns, normal polarity
   pwm-2   (sysfs               ): requested
  	requested configuration:  enabled, 121568/1000000 ns, normal polarity
  	actual configuration:    disabled, 0/0 ns, normal polarity
   pwm-3   ((null)              ):
  	requested configuration: disabled, 0/0 ns, normal polarity
  	actual configuration:    disabled, 0/0 ns, normal polarity
  
  1: platform/1f0009c000.pwm, npwm: 4
   pwm-0   ((null)              ):
  	requested configuration: disabled, 0/0 ns, normal polarity
  	actual configuration:    disabled, 0/0 ns, normal polarity
   pwm-1   ((null)              ):
  	requested configuration: disabled, 0/0 ns, normal polarity
  	actual configuration:    disabled, 0/0 ns, normal polarity
   pwm-2   ((null)              ):
  	requested configuration: disabled, 0/0 ns, normal polarity
  	actual configuration:    disabled, 0/0 ns, normal polarity
   pwm-3   (cooling_fan         ): requested
  	requested configuration: disabled, 0/41566 ns, inverse polarity, usage_power
  	actual configuration:    disabled, 0/0 ns, normal polarity
  

  其中：

  • ＂0＂-＂pwm-2＂是示例项
  • ＂1＂-＂pwm-3＂是风扇

• 用gpioinfo -c 0 18检查＂gpiochip0＂＼line 18——GPIO18的配置，有：＂gpiochip0 18 "GPIO18" input＂（而非＇gpiochip0 18 "GPIO18" PWM0_CHAN2＇）

• 用pinctrl 18检查有：＂18: a3 pd | lo // GPIO18 = PWM0_CHAN2＂。

• 使用pinctrl funcs查看GPIO支持的功能，（用pinctrl funcs | grep PWM筛选）。
  其中GPIO12、13、14、15、18、19支持硬件PWM。（软PWM见＂/boot/firmware/overlays/README＂中的＂pwm-gpio＂）

• ＂PWM0_CHAN2＂对应

  • bash中的＂pwmchip0＂，lua-peripheral中的＂PWM_CHIP=0＂；
  • bash中的＂pwm2＂，lua-peripheral中的＂PWM_CHANNEL=2＂。

• 支持的PWM针脚，可参考PWM at Raspberry Pi GPIO Pinout