这是一段关于凤鸣器的驱动，用pwm来控制频率，可以实现不同的波段的声音-This is a paragraph on the drive Fengming, using pwm to control the frequency band can achieve different sounds

s3c2410 改变pwm可使蜂鸣器发出不同频率声音-s3c2410 pwm can change the beeper sounds at different frequencies