Product manual

Spinpoint M9TU-USB 3.0 Product Manual REV 1.0
71
USB INTERFACE AND USB COMMANDS
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 maximum
packet size for the endpoint can be any allowed value (as defined in Chapter 5). If bits 12..11 of wMaxPacketSize
are not zero (0), the allowed values for wMaxPacketSize bits 10..0 are limited as shown in Table 6-17.