The Host Controller (HC) contains a set of on-chip operational registers which are mapped into a noncacheable portion of the system addressable space. These registers are used by the Host Controller Driver (HCD). According to the function of these registers, they are divided into four partitions, specifically for Control and Status, Memory Pointer, Frame Counter and Root Hub. All of the registers should be read and written as Dwords.

    上文:
    主机控制器(HC)内置一组片上操作寄存器,这些寄存器被映射至系统可寻址空间中的非缓存区域。主机控制器驱动程序(HCD)通过访问这些寄存器实现控制功能。根据寄存器功能划分,其分为四个独立分区:控制与状态寄存器组、内存指针寄存器组、帧计数器寄存器组以及根集线器寄存器组。所有寄存器均须以双字(Dword)为单位进行读写操作。

    specifically
    美 [spə’sɪfɪkli]
    英 [spɪˈsɪfɪklɪ]
    adv. 特意;特别地;专门地;具体说来;确切地说;明确地;具体地;特定地;专有地;

    Dwords
    双字,在本文档中应该指4B。

    Reserved bits may be allocated in future releases of this specification. To ensure interoperability, the Host Controller Driver that does not use a reserved field should not assume that the reserved field contains 0. Furthermore, the Host Controller Driver should always preserve the value(s) of the reserved field. When a R/W register is modified, the Host Controller Driver should first read the register, modify the bits desired, then write the register with the reserved bits still containing the read value. Alternatively, the Host Controller Driver can maintain an in-memory copy of previously written values that can be modified and then written to the Host Controller register. When a write to set/clear register is written, bits written to reserved fields should be 0.

    上文:
    保留位可能在本规范的未来版本中被分配使用。为确保互操作性,不使用保留字段的主机控制器驱动程序(HCD)不应假定保留字段的值为0。此外,主机控制器驱动程序应始终保留保留字段的值。当修改可读/写寄存器时,主机控制器驱动程序应先读取寄存器,修改所需位,然后将保留位仍保持的读取值写入到寄存器。或者,主机控制器驱动程序可以维护先前写入值的内存副本,这些值可以被修改后写入主机控制器寄存器。当写入设置/清除寄存器时,写入保留字段的位应为0。

    interoperability
    英 [ˈɪntəˌrɒpərəˈbɪlɪtɪ]
    n. 互操作性