友好的arm mini2440中的PWM QT GUI

Question

我正在使用mini2440主板。我想为pwm开发一个可以增加和减少信号频率的gui。它有四个按钮 - 开始，停止，最大和最小 - 但按下最大按钮不会改变频率。通过使用启动和停止gui程序终止但仍然pwm打开，我的意思是蜂鸣器开启。

这是代码

#include "hello.h"
#include <qlabel.h>
#include <qpushbutton.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <linux/fs.h>
#include <errno.h>
#include <string.h>
#include <qobject.h>
#include <fstream>
#include <linux/i2c-dev.h>
#include <string.h>            
#include <stdio.h>                        
#include <linux/fs.h>
#include <termios.h>        //Headers
#include <stdint.h>
#include <getopt.h>
#include <linux/types.h>
#include <linux/spi/spidev.h>
#include <time.h>
#include <string.h>
#include <sys/time.h>
#define PWM_IOCTL_SET_FREQ      1  
#define PWM_IOCTL_STOP          0  

int freq=1000;
int fd;

HelloForm::HelloForm( QWidget* parent, const char* name, WFlags fl)
     :HelloBaseForm(parent, name, fl)
{
     connect(PushButton33,SIGNAL(clicked()),this,SLOT(start()));
     connect(PushButton30,SIGNAL(clicked()),this,SLOT(stop()));
     connect(PushButton31,SIGNAL(clicked()),this,SLOT(plus()));
     connect(PushButton32,SIGNAL(clicked()),this,SLOT(minus()));
}

HelloForm::~HelloForm()
{

}

// this is start button
void HelloForm::start()
{
     int fd = open("/dev/pwm", 0);

     if (fd < 0) {
          status->setText("open pwm_buzzer device");
     }
     else {
          status->setText("start");
     }
     ioctl(fd, PWM_IOCTL_SET_FREQ, freq);
     pwm->setText(QString::number(freq));
     //close(fd);
}

//stop button
void HelloForm::stop()
{
     close(fd);
     int fd=open("/dev/pwm",0); //File handler
     ioctl(fd, PWM_IOCTL_STOP);  // stop the ioctl
     close(fd); 
}

// increase the pwm
void HelloForm::plus()
{
     if(freq<20000)
     {
          freq+=10;
          ioctl(fd,PWM_IOCTL_SET_FREQ,freq); //freq set
          pwm->setText(QString::number(freq));
     }
}

void HelloForm::minus()
{
     if(freq>11)
     {
          freq-=10;
          ioctl(fd,PWM_IOCTL_SET_FREQ,freq);
          pwm->setText(QString::number(freq));
     }
}