EP80579 Datasheet, PDF (968/1916 Pages) Intel Corporation – Intel® EP80579 Integrated Processor Product Line

Intel^® EP80579 Integrated Processor
QH (Queue Element Link Pointer)→ TD
→ Write-Back to QH (Queue Element Link Pointer)
→ QH (Queue Head Link pointer).
Breadth-First is also performed for every transaction execution that fails the advance
criteria. This means that if a queued TD fails, the queue does not advance, and the CMI
traverses the QH’s Queue Head Link Pointer.
In a Depth-first traversal, the top queue element must complete successfully to satisfy
the advance criteria for the queue. If the CMI is currently processing a queue, and the
advance criteria are met, and the Vf bit is set, the CMI follows the TD’s link pointer to
the next schedule work item.
Regardless of traversal model, when the advance criteria are met, the successful TD’s
link pointer is written back to the QH’s Queue Element link pointer.
When the CMI encounters a QH, it caches the QH internally, and sets internal state to
indicate it is in a Q-context. It needs this state to update the correct QH (for auto
advancement) and also to make the correct decisions on how to traverse the Frame
List.
Restricting the advancement of queues to advancement criteria implements a
guaranteed data delivery stream.
A queue is never advanced on an error completion status (even in the event the error
count was exhausted).
Table 25-29 lists the general queue advance criteria, which are based on the execution
status of the TD at the ‘Top’ of a currently ‘active’ queue.
Table 25-29. Queue Advance Criteria
Function-to-Host (IN)
Non-NULL
Advance Q
NULL
Advance Q
Error/NAK
Retry Q Element
Host-to-Function (OUT)
Non-NULL
Advance Q
NULL
Advance Q
Error/NAK
Retry Q Element
Table 25-30 is a decision table illustrating the valid combinations of link pointer bits and
the valid actions taken when advancement criteria for a queued transfer descriptor are
met. The column headings for the link pointer fields are encoded, based on the
following list:
Legend:
QH.LP = Queue Head Link Pointer (or Horizontal Link Pointer)QE.Q = Q bit in QE
QE.LP = Queue Element Link Pointer (or Vertical Link Pointer)QE.T = T bit in QE
TD.LP = TD Link PointerTD. Vf = Vf bit in TD
QH.Q = Q bit in QH TD.Q = Q bit in TD
QH.T = T bit in QH TD. Vf = Vf bit in TD
Intel^® EP80579 Integrated Processor Product Line Datasheet
968
August 2009
Order Number: 320066-003US