Information Technology Reference
In-Depth Information
Figure 11-1: Requests sent by a Windows host to enumerate a mass-storage
device. (Screen capture from Ellisys USB Explorer.)
is one example of host communications. Hosts aren't required to use this
exact sequence of requests. The device doesn't need to know or care why the
host is sending a request or resetting the bus and shouldn't assume anything
about what a host will do next. The device just needs to respond appropri-
ately when something happens.
Mass Storage Functions
After enumeration, a host can use USB requests and SCSI commands to
learn more about a device and to prepare to read and write to the storage
media. Figure 11-2 shows communications from a Windows host after com-
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