这篇文档主要介绍如何使用硬件PWM（Pulse Width Modulation）。
设置以及打开PWM
PWM_F：
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| $ echo 1 | sudo tee /sys/class/pwm/pwmchip4/export
$ echo 1000000 | sudo tee /sys/class/pwm/pwmchip4/pwm1/period
$ echo 500000 | sudo tee /sys/class/pwm/pwmchip4/pwm1/duty_cycle
$ echo 1 | sudo tee /sys/class/pwm/pwmchip4/pwm1/enable
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PWM_D：
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| $ echo 1 | sudo tee /sys/class/pwm/pwmchip1/export
$ echo 1000000 | sudo tee /sys/class/pwm/pwmchip1/pwm1/period
$ echo 500000 | sudo tee /sys/class/pwm/pwmchip1/pwm1/duty_cycle
$ echo 1 | sudo tee /sys/class/pwm/pwmchip1/pwm1/enable
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PWM_F：
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| $ echo 1 | sudo tee /sys/class/pwm/pwmchip4/export
$ echo 1000000 | sudo tee /sys/class/pwm/pwmchip4/pwm1/period
$ echo 500000 | sudo tee /sys/class/pwm/pwmchip4/pwm1/duty_cycle
$ echo 1 | sudo tee /sys/class/pwm/pwmchip4/pwm1/enable
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PWM_F：
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| $ echo 1 | sudo tee /sys/class/pwm/pwmchip4/export
$ echo 1000000 | sudo tee /sys/class/pwm/pwmchip4/pwm1/period
$ echo 500000 | sudo tee /sys/class/pwm/pwmchip4/pwm1/duty_cycle
$ echo 1 | sudo tee /sys/class/pwm/pwmchip4/pwm1/enable
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如果你成功开启了硬件PWM，你可以通过示波器看到波形：
注意如果使用示波器去查看波形,记得板子和示波器需要共地。
关闭PWM
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| $ echo 0 | sudo tee /sys/class/pwm/pwmchip4/pwm1/enable
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| $ echo 0 | sudo tee /sys/class/pwm/pwmchip1/pwm1/enable
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1
| $ echo 0 | sudo tee /sys/class/pwm/pwmchip4/pwm1/enable
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| $ echo 0 | sudo tee /sys/class/pwm/pwmchip4/pwm1/enable
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