I am writing a QNX USB driver program. 
USB device is inserted into the PC. Device is detected by my driver.
Now, I want to get the audio data from device by urb. firstly, I must check the status of the urb.
I used the function: usbd_urb_status(urb, &ustatus, &receive_len)
Parameter ustatus is stored the urb's status.
Then I did what I wrote under:
①	check the value of ustatus, ustatus: USBD_STATUS_CMP_ERR（The operation is complete, but an error occurred）
②	check the returned value of the usbd_urb_status(),returned value is EIO（I/O error）
So, my question is : what is the reason of EIO occurred 
PS: I think the data transfer got some error occurred, but I don't know what wrong with the data transfer.

Thanks for your suggestion!!