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In frame N (micro-frames 0-7), for this example, the host controller will traverse all of
the schedule data structures utilizing the Normal Path Link Pointers in any FSTNs it
encounters. This is because the host controller has not yet encountered a Save-Place
FSTN so it not executing in Recovery Path mode. When it encounters the Restore FSTN,
(Restore-N), during micro-frames 0 and 1, it uses Restore-N.Normal Path Link Pointer
to traverse to the next data structure (i.e. normal schedule traversal). This is because
the host controller must use a Restore FSTN's Normal Path Link Pointer when not
executing in a Recovery-Path mode. The nodes traversed during frame N include:
{8
, 8
2.0
2.1
In frame N+1 (micro-frames 0 and 1), when the host controller encounters Save-Path
FSTN (Save-N), it observes that Save-N.Back Path Link Pointer.T-bit is zero (definition
of a Save-Path indicator). The host controller saves the value of Save-N.Normal Path
Link Pointer and follows Save-N.Back Path Link Pointer. At the same time, it sets an
internal flag indicating that it is now in Recovery Path mode (the recovery path is
annotated in
on page 459
structures on the recovery path and executing only those bus transactions as noted
above, on the recovery path until it reaches Restore FSTN (Restore-N). Restore-N.Back
Path Link Pointer.T-bit is set to a one (definition of a Restore indicator), so the host
controller exits Recovery Path mode by clearing the internal Recovery Path mode flag
and commences (restores) schedule traversal using the saved value of the Save-Place
FSTN's Normal Path Link Pointer (e.g. Save-N.Normal Path Link Pointer). The nodes
traversed during these micro-frames include: {8
2
, Restore-N, 4
0
faced.
In frame N+1 (micro-frames 2-7), when the host controller encounters Save-Path FSTN
Save-N, it will unconditionally follow Save-N.Normal Path Link Pointer. The nodes
traversed during these micro-frames include: {8
N, 1
...}.
0
Software Operational Model for FSTNs
Software must create a consistent, coherent schedule for the host controller to
traverse. When using FSTNs, system software must adhere to the following rules:
• Each Save-Place indicator requires a matching Restore indicator.
The Save-Place indicator is an FSTN with a valid Back Path Link Pointer and T-bit equal
to zero. Note that Back Path Link Pointer.Typ field must be set to indicate the
referenced data structure is a queue head. The Restore indicator is an FSTN with its
Back Path Link Pointer.T-bit set to a one.
A Restore FSTN may be matched to one or more Save-Place FSTNs. For example, if the
schedule includes a poll-rate 1 level, then system software only needs to place a
Restore FSTN at the beginning of this list in order to match all possible Save-Place
FSTNs.
• If the schedule does not have elements linked at a poll-rate level of one, and one or
more Save-Place FSTNs are used, then System Software must ensure the Restore
FSTN's Normal Path Link Pointer's T-bit is set to a one, as this will be use to mark
the end of the periodic list.
• When the schedule does have elements linked at a poll rate level of one, a Restore
FSTN must be the first data structure on the poll rate one list. All traversal paths
from the frame list converge on the poll-rate one list. System software must ensure
that Recovery Path mode is exited before the host controller is allowed to traverse
the poll rate level one list.
• A Save-Place FSTN's Back Path Link Pointer must reference a queue head data
structure. The referenced queue head must be reachable from the previous frame
list location. In other words, if the Save-Place FSTN is reachable from frame list
®
®
Intel
IXP45X and Intel
IXP46X Product Line of Network Processors
Developer's Manual
460
®
®
IXP45X and Intel
IXP46X Product Line of Network Processors—USB 2.0 Host Controller
, 8
, 8
, 4
, 2
, Restore-N, 1
2.2
2.3
2
0
Figure 70, "Example Host Controller Traversal of Recovery Path via FSTNs"
with a large dashed line). The host controller continues traversing data
, 2
, Restore-N, 1
3
1
...}.
0
, 8
, 8
3.0
3.1
...}. The nodes on the recovery-path are bold
0
, 8
, 8
3.0
3.1
3.2
, Save-A, 8
, 8
3.2
2.2
2.3
, Save-A, 4
, 2
, Restore-
3
1
August 2006
Order Number: 306262-004US
, 4
,
2
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