Managing Isochronous Transfers Using Itds; Host Controller Operational Model For Itds; Example Periodic Schedule - Intel IXP45X Developer's Manual

Intel
Figure 59.

Example Periodic Schedule

1024, 512, or 256
9.14.7

Managing Isochronous Transfers Using iTDs

The structure of an iTD is presented in
Transfer Descriptor (iTD)" on page
• The first field is the Next Link Pointer. This field is for schedule linkage purposes
only;
• Transaction description array. This area is an eight-element array. Each element
represents control and status information for one micro-frame's worth of
transactions for a single high-speed isochronous endpoint.
• The buffer page pointer array is a 7-element array of physical memory pointers to
data buffers. These are 4K aligned pointers to physical memory.
• Endpoint capabilities. This area utilizes the unused low-order 12 bits of the buffer
page pointer array. The fields in this area are used across all transactions executed
for this iTD, including endpoint addressing, transfer direction, maximum packet size
and high-bandwidth multiplier.
9.14.7.1

Host Controller Operational Model for iTDs

The host controller uses FRINDEX register bits [12:3] to index into the periodic frame
list. This means that the host controller visits each frame list element eight consecutive
times before incrementing to the next periodic frame list element. Each iTD contains
eight transaction descriptions, which map directly to FRINDEX register bits [2:0]. Each
iTD can span 8 micro-frames worth of transactions. When the host controller fetches an
iTD, it uses FRINDEX register bits [2:0] to index into the transaction description array.
If the active bit in the Status field of the indexed transaction description is set to zero,
the host controller ignores the iTD and follows the Next pointer to the next schedule
data structure.
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Intel IXP45X and Intel IXP46X Product Line of Network Processors
Developer's Manual
426
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IXP45X and Intel IXP46X Product Line of Network Processors—USB 2.0 Host Controller
Periodic Frame List
elements
Isochronous Transfer
Descriptor(s)
Poll Rate: 1 Poll Rate: N
Section 9.13.3, "Isochronous (High-Speed)
391. There are four distinct sections to an iTD:
Last
Periodic
has End of
List mark
Interrupt Queue
Heads
1
B4502-01
August 2006
Order Number: 306262-004US