Solution:

The field EVENT is relate to FIFO. For example, if the card with on-board 1K bytes FIFO, and user set this field to 512. That this structure will generate the INTERRUPT while half or full of FIFO buffer. On the other hand, if the card without on-board FIFO, and user set this field to 1. Then this structure will generate the INTERRUPT every time you receive one data. Besides, this structure is for all types of event. However, user just can use one event at a time.