FW82801EB Intel, FW82801EB Datasheet - Page 202

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FW82801EB

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FW82801EB
Description
Manufacturer
Intel
Datasheet

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Functional Description
202
Table 90. Queue Advance Criteria
The traversal has two options: Breadth first, or Depth first. A flag bit in each TD (Vf — Vertical
Traversal Flag) controls whether traversal is Breadth or Depth first. The default mode of traversal
is Breadth-First. For Breadth-First, the ICH5 only executes the top element from each queue. The
execution path is shown below:
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 ICH5 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 ICH5 is currently processing a queue, and the advance criteria are met,
and the Vf bit is set, the ICH5 follows the TD’s link pointer to the next schedule work item.
Note that 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 ICH5 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 90
at the “Top” of a currently “active” queue.
Table 91
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:
1. QH (Queue Element Link Pointer)
2. TD
3. Write-Back to QH (Queue Element Link Pointer)
4. QH (Queue Head Link pointer).
Non-NULL
Advance Q
lists the general queue advance criteria, which are based on the execution status of the TD
is a decision table illustrating the valid combinations of link pointer bits and the valid
Function-to-Host (IN)
Advance Q
NULL
Retry Q Element
Error/NAK
Intel
Non-NULL
Advance Q
®
82801EB ICH5 / 82801ER ICH5R Datasheet
Host-to-Function (OUT)
Advance Q
NULL
Retry Q Element
Error/NAK

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