Instrumentation level: in this level, the manageable endpoints (device, software service, and so on) are made accessible through JMX-specified interfaces.
工具层：在本层，可管理端点(设备、软件服务等)可通过JMX指定的接口访问。
A given USB device may have many endpoints, and the number of data pipes between the host and the device is the same as the number of endpoints on the device.
一个给定的USB设备可以有许多个端点，主机与设备之间数据管道的数量与该设备上端点的数量相同。
EPCTL controls the 3 pairs of endpoints of the device controller's writing and reading operations.
EPCTL 完成设备控制器内集成的3 对端点缓冲区的读写控制。
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