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Chapter 4

 

Data Flow Model

Wireless Universal Serial Bus Specification, Revision 1.0

Host Transmit Window

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Figure 4-41 Receive window after receiving a WISOCH_DISCARD IE subsequent to a lost ACK.

4.11.8Synchronization

To allow for synchronization of clocks between Wireless USB devices, the Wireless USB host must provide a Wireless USB channel time stamp in each MMC. This time stamp provides similar functionality for isochronous function endpoints needing synchronization as the indexed (micro)SOFs provided in USB 2.0. The time stamp format and accuracy requirements are described in Sections 4.3.1, 4.3.2 and 4.3.3.

4.11.8.1Synchronizing a Stream Start Time

The unreliable wireless media creates a problem for stream synchronization. In wired USB the time at which an isochronous IN function endpoint starts producing data is deterministic. Consider a typical wired isochronous IN device with two (micro) frames of buffering. The (micro) frame in which the first data request is made is specified as frame (microframe) X. The data returned by the device in response to the request in frame X is produced starting at the beginning of frame X-1.

In wireless USB the time when data is first produced for a wireless USB isochronous IN stream is less deterministic. The layout of reservations in the superframe (if the Wireless USB host is sharing it with other

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Соседние файлы в папке Wireless USB Specification Revision 1.0 May 12, 2005