The Host Controller Communications Area (HCCA) is a 256-byte structure of system memory that is used by system software to send and receive specific control and status information to and from the HC. This structure must be located on a 256-byte boundary. System software must write the address of this structure in HcHCCA in the HC. This structure allows the software to direct the HC’s functions without having to read from the Host Controller except in unusual circumstances (e.g., error conditions). Normal interaction with the Host Controller can be accomplished by reading values from this structure that were written by the Host Controller and by writing to the HC’s operation registers.
Note: It is expected that writes to the Host Controller will be posted and have minimal impact on CPU performance.

主机控制器通信区域（HCCA）是一个256字节的系统内存结构，系统软件通过该结构与HC（主机控制器）收发特定的控制和状态信息。此结构必须位于256字节边界上。系统软件必须将该结构的地址写入HC的HcHCCA寄存器中。此结构允许软件在无需读取主机控制器的情况下（异常情况除外，如错误状态）控制HC的功能。通过与主机控制器的正常交互，可通过读取主机控制器写入此结构的值以及写入HC的操作寄存器来实现。

注：对主机控制器的写操作预计将被缓存，并且对CPU性能的影响极小。