是否可以在不关闭文件描述符的情况下读取 Beaglebone Black 或其他嵌入式 Linux 系统的 ADC？
我之前用 select 试过read()。select()返回 1，但read()在第一次迭代后返回 0，因此我无法获取任何数据。有任何想法吗？关闭和打开文件描述符是否需要大量 CPU 资源？
我的代码：
#include<iostream>
#include<fstream>
#include<string.h>
#include<sstream>
#include<fcntl.h>
#include<unistd.h>
#include<sys/select.h>
#include <sys/time.h>
using namespace std;
#define LDR_PATH "/sys/bus/iio/devices/iio:device0/in_voltage"
int main(int argc, char* argv[]){
int number = 1;
int AdcConnection = 0;
stringstream AdcPath;
AdcPath << LDR_PATH << number << "_raw";
AdcConnection = open(AdcPath.str().c_str(),O_RDONLY |O_NONBLOCK);
if (AdcConnection <0)
{
perror("UART: Failed to open the file.\n");
close(AdcConnection);
return -1;
}
fd_set fdsAdcRead;
struct timeval timeout = {5, 0};
unsigned char receive[5];
int FlagRead = -1;
int FlagSelect = -1;
while (1)
{
FD_ZERO(&fdsAdcRead); //clear the file descriptor
FD_SET(AdcConnection,&fdsAdcRead); //Set the descriptor
FlagSelect = select(AdcConnection+1,&fdsAdcRead,NULL,NULL,&timeout);//check if data are available
if (FlagSelect <0)
{
perror("Failed to check if data are available.\n");
close(AdcConnection);
return -1;
}
else if (FlagSelect ==0)
{
cout << "There were no Data" << endl;
timeout.tv_sec = 5;
}
else
{
memset(&receive,0,sizeof(receive));
FlagRead = read(AdcConnection, (void*)receive, 5);
cout << receive << endl << FlagRead << FlagSelect << endl;
timeout.tv_sec = 5;
}
usleep(1000000);
}