通過打開和讀取檢測可用設備

Question

說我打開設備。

int fd,fd1; 
fd_set readfds; 
int maxfd; 

fd = open("/dev/ttyUSB0"); 
if(fd<0) printf("device not available\n");//How can i Wait here until device becomes available?.. Also when it shows device not available it will just continue on doing select. 
printf("device /dev/ttyUSB0 available\n"); 

fd1 = open("/dev/ttyUSB1"); 
if(fd<0) printf("device not available\n");//How can i Wait here until device becomes available? 
printf("device /dev/ttyUSB1 available\n"); 

maxfd = MAX(fd,fd1)+1; 

現在我將它們添加到fd_set;

while(1){ 

FD_SET(fd,&readfds); 
FD_SET(fd1,&readfds); 

select(maxfd, &readfds, NULL, NULL, NULL); 

if(FD_ISSET(fd,&readfds){ 

// Read the device. If there is nothing to read then device has been removed or something happend. 

} 

if(FD_ISSET(fd1,&readfds){ 

// Read the device. If there is nothing to read then device has been removed or something happend. 

} 


} 

現在我該如何檢查設備現在可用。說，如果設備不可用，當我打開它。我如何監控它以檢查它何時被插入？我不想使用udev/libudev.h。

感謝，

Answer 1

常見的方法是嘗試寫入設備的某些數據並讀迴響應。如果預期響應，則意味着設備已連接，否則不是。

例如，當掃描連接了調制解調器的COM端口時，應該將"ATE0\r"寫入COM端口並取回調制解調器響應"OK"。這意味着調制解調器連接到該COM端口。

同樣的想法適用於USB設備。只有協議更復雜，並且請求/響應數據在設備之間可能更復雜。