1394规范，The 1394 Open Host Controller Interface (Open HCI) is an implementation of the link layer protocol of the 1394 Serial
Bus, with additional features to support the transaction and bus management layers. The 1394 Open HCI also includes
DMA engines for high-performance data transfer and a host bus interface.
IEEE 1394 (and the 1394 Open HCI) supports two types of data transfer: asynchronous and isochronous. Asynchronous
data transfer puts the emphasis on guaranteed delivery of data, with less emphasis on guaranteed timing. Isochronous data
transfer is the opposite, with the emphasis on the guaranteed timing of the data, and less emphasis on delivery.
