Intel 6 SERIES CHIPSET - SPECIFICATION UPDATE 01-2011 Specification page 14

6. Asynchronous Retries Prioritized Over Periodic Transfers
Problem: The integr ated USB
asynchronous retries over dispatchable periodic transfers.
Implication: Periodic transfers may be delayed or aborted. If the asynchronous retry latency causes
the periodi c transfer to be aborted,
periodic transfer:
• If a periodic interrupt transfer is aborted, the data may be recovered by the next
instance of the interrupt or the data could be dropped.
• If a periodic isochronous transfer is aborted, the data will be dropped. A single
dropped periodic transaction should not be noticeable by end user.
Note: This issue has only been seen in a synthetic environment. The USB spec does not
consider the occasional loss of periodic traffic a violation.
Workaround: None.
Status: No Plan to Fix.
7. USB FS/LS Incorrect Number of Retries
Problem: A USB Lo w-Speed T ransaction ma y be retried more than three times, and
Full-Speed tr ansaction may be retried
conditions are met:
• A USB Low-Speed transaction with errors, or the first retry of the transaction
occurs near the end of a micro-frame, and there is not enough time to complete
another retry of the Low-Speed transaction in the same micro-frame
• There is pending USB Full-Speed traffic and there is enough time left in the
micro-frame to complete one or more attempts of the Full-Speed transaction
• Both the Low-Speed and Full-Speed transactions must be asynchronous
(Bulk/Control) and must have the same direction either in or out
Note: Note: Per the USB EHCI Specification a transaction with errors should be attempted a
maximum of 3 times if it continues to fail.
Implication:
• For Low-Speed transactions the extra retry(s) allow a transaction additional
chance(s) to recover regardless of if the Full-Speed transaction has errors or not.
• If the Full-Speed transactions also have errors, the PCH may retry the transaction
fewer times than required, stalling the device prematurely. Once stalled, the
implication is software dependent, but the device may be reset by software.
Workaround: None.
Status: No Plan to Fix.
14
RMH incorrectly prioritizes Full-Sp eed and
the impact v aries depending on the nature of
less than three times if all
Errata
Low-Speed
a USB
of the followin g
Specification Update