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上一帖中已经成功使用一个简单的main函数成功读取到DHT11的温湿度数据了，虽然读取温湿度数据响应时间很慢，但至少算是成功读取了，这次我就想在QT环境下进行温湿度的读取，结合美观的图形界面呈现出来，同时，还可以以文件形式读取AD[color=inherit !important]C_IN4接口 CPU0温度以及CPU1温度，使用到的QT类为Q[color=inherit !important]Thread，还有[color=inherit !important]Linux系统自带的pthread。为什么说是波折经历呢，因为DHT11这个器件对主控和系统的实时性要求实在是太高了，如果是直接用单片机主控来读取，那就没任何问题，但是要用到微处理器，哪怕是[color=inherit !important]RK3399这种主频那么高的CPU，读取DHT11依然会出现实时性问题，这就很烦，由于QT的图形化界面用到了QMainWindow类，会占用一定的CPU实时资源，在这一两天的探索过程中，我先后用了QThread pthread QTimer三种方式读取DHT11数据，结果表明，要想稳定读取，只能用pthread进行，QThread这种QT内建的多线程实现类完全无法读取，顶多只能读取已经存在/sys中的实时CPU温度数据和ADC接口数据，而QTimer这种定时器中断类就更不用说了，实时性比QThread还低得多，跟pthread的效率比起来就没法比。我不知道QThread的实现代码是怎么写的，按我理解来说应该也只是对pthread做一定的封装，也没想到实时性/效率差这么远。
首先是读写两个CPUzone的温度，需要读取/sys/class/thermal/thermal_zone0/temp和/sys/class/thermal/thermal_zone1/temp：int fd_cputemp0，fd_cputemp1;unsigned char buf_cpu_temp0[5];unsigned char buf_cpu_temp1[5];fd_cputemp0 = open("/sys/class/thermal/thermal_zone0/temp", O_RDONLY);fd_cputemp1 = open("/sys/class/thermal/thermal_zone1/temp", O_RDONLY);read(fd_adc4 , buf_adc4 ,5);read(fd_cputemp0 , buf_cpu_temp0 ,5);read(fd_cputemp1 , buf_cpu_temp1 ,5);
而ADC_IN4则是用同样的方法读取/sys/bus/iio/devices/iio:device0/in_voltage4_raw：int fd_adc4;unsigned char buf_adc4[5];fd_adc4 = open("/sys/bus/iio/devices/iio:device0/in_voltage4_raw", O_RDONLY);read(fd_adc4 , buf_adc4 ,5);
然后是对于DHT11的读取，原本我是打算使用QThread来进行读取了，也写好了QThread类：
#ifndef MY_THREAD_H#define MY_THREAD_H#include <QThread>#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <sys/time.h>#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include "mainwindow.h"class MainWindow;class mythread : public QThread{public: mythread(QObject *parent); void closeThread(); struct timeval tv1;protected: virtual void run();private: volatile bool isStop; MainWindow *m_pMainWindow; int fd_cputemp0,fd_cputemp1,fd_adc4;};#endif // DHT11_THREAD_H
#include "mythread.h"#include "mainwindow.h"#include <ui_mainwindow.h>mythread::mythread(QObject *parent){ isStop = false; m_pMainWindow = qobject_cast<MainWindow*>(parent);}void mythread::closeThread(){ isStop = true;}extern float dht11_temp,dht11_humi;void mythread::run(){ int i=0; unsigned char buf_adc4[5]; unsigned char buf_cpu_temp0[5]; unsigned char buf_cpu_temp1[5]; while (1) { if(isStop) return; //gettimeofday(&tv1, NULL); //qDebug("tv1=%d\n",tv1.tv_usec); fd_adc4 = open("/sys/bus/iio/devices/iio:device0/in_voltage4_raw", O_RDONLY); fd_cputemp0 = open("/sys/class/thermal/thermal_zone0/temp", O_RDONLY); fd_cputemp1 = open("/sys/class/thermal/thermal_zone1/temp", O_RDONLY); read(fd_adc4 , buf_adc4 ,5); read(fd_cputemp0 , buf_cpu_temp0 ,5); read(fd_cputemp1 , buf_cpu_temp1 ,5); buf_adc4[4]=0; m_pMainWindow->ui->L1->setText(QString("%1").arg(dht11_temp)); m_pMainWindow->ui->L2->setText(QString("%1").arg(dht11_humi)); m_pMainWindow->ui->L3->setText(QString((char*)buf_adc4)); m_pMainWindow->ui->L4->setText(QString((char*)buf_cpu_temp0)); m_pMainWindow->ui->L5->setText(QString((char*)buf_cpu_temp1)); sleep(1); }}
谁知道读取不成功，估计是read函数所在线程被CPU打断了，无奈之下只能换成Linux最基本的pthread实现方式：struct dht11_data{ unsigned short temp; unsigned short hum;}curdht11_data;float dht11_temp,dht11_humi;pthread_t id;int fd_dht11;void *Thread_CPU_Temp(void *arg){ int retval; while(1) { retval = read ( fd_dht11 , &curdht11_data , sizeof(curdht11_data) ); if ( retval == -1 ) { printf ( "read dht11 error" ) ; } if(curdht11_data.temp != 0xffff) { if(0 < (curdht11_data.temp>>8) && (curdht11_data.temp>>8) < 85) { dht11_temp = (curdht11_data.temp >> 8) + (curdht11_data.temp & 0xff) * 0.01; dht11_humi = (curdht11_data.hum >> 8) + (curdht11_data.hum & 0xff) * 0.01; printf("---- %f %f-----\n",dht11_temp,dht11_humi); } } //sleep(1); }}
这样的话可以正常读取，由此判断pthread实现方式能抢占到更多的CPU资源，并且pthread线程创建必须在MainWindow主窗口之前：int main(int argc, char *argv[]){ QApplication a(argc, argv); fd_dht11 = open ( "/dev/dht11" , O_RDONLY) ; if ( fd_dht11 == -1 ) { perror ( "open dht11 error\n" ) ; } printf ( "open /dev/dht11 successfully\n" ) ; pthread_create(&id , NULL , Thread_CPU_Temp , NULL); printf ( "create pthread successfully\n" ) ; MainWindow w; w.show(); return a.exec();}
QThread线程就只拿来读取CPU0温度，CPU1温度和ADC_IN4通道，Qthread线程的运行和暂停又一个按钮来控制：void MainWindow::on_PB1_clicked(){ disconnect(ui->PB1,SIGNAL(clicked()),this,SLOT(on_PB1_clicked())); connect(ui->PB1,SIGNAL(clicked()),this,SLOT(on_PB1_clicked_2())); ui->PB1->setText("Pause"); thread1->start();}void MainWindow::on_PB1_clicked_2(){ disconnect(ui->PB1,SIGNAL(clicked()),this,SLOT(on_PB1_clicked_2())); connect(ui->PB1,SIGNAL(clicked()),this,SLOT(on_PB1_clicked())); ui->PB1->setText("Start"); thread1->closeThread(); thread1->wait();}
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