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Spinpoint M8U-Internal Product Manual REV 3.4
81
INSTALLATION
The bmAttributes field provides information about the endpoint’s Transfer Type (bits 1..0) and
Synchronization Type (bits 3..2). In addition, the Usage Type bit (bits 5..4) indicate whether this is an
endpoint used for normal data transfers (bits 5..4=00B), whether it is used to convey explicit feedback
information for one or more data endpoints (bits 5..4=01B) or whether it is a data endpoint that also serves as
an implicit feedback endpoint for one or more data endpoints (bits 5..4=10B). Bits 5..2 are only meaningful
for isochronous endpoints and must be reset to zero for all other transfer types.
If the endpoint is used as an explicit feedback endpoint (bits 5..4=01B), then the Transfer Type must be set to
isochronous (bits1..0 = 01B) and the Synchronization Type must be set to No Synchronization (bits
3..2=00B).
A feedback endpoint (explicit or implicit) needs to be associated with one (or more) isochronous data
endpoints to which it provides feedback service. The association is based on endpoint number matching. A
feedback endpoint always has the opposite direction from the data endpoint(s) it services. If multiple data
endpoints are to be serviced by the same feedback endpoint, the data endpoints must have ascending ordered–
but not necessarily consecutive–endpoint numbers. The first data endpoint and the feedback endpoint must
have the same endpoint number (and opposite direction). This ensures that a data endpoint can
uniquely
identify its feedback endpoint by searching for the first feedback endpoint that has an endpoint number equal
or less than its own endpoint number.
High-speed isochronous and interrupt endpoints use bits 12..11 of wMaxPacketSize to specify multiple
transactions for each microframe specified by bInterval. If bits 12..11 of wMaxPacketSize are zero, the