Queue Element Transfer Descriptor (Qtd); Queue Element Transfer Descriptor Block Diagram; Sitd Back Link Pointer - Intel IXP45X Developer's Manual

USB 2.0 Host Controller—Intel
Table 155.

siTD Back Link Pointer

Bit
31:5
4:1
0
9.13.5

Queue Element Transfer Descriptor (qTD)

This data structure is only used with a queue head. This data structure is used for one
or more USB transactions. This data structure is used to transfer up to 20480 (5*4096)
bytes. The structure contains two structure pointers used for queue advancement, a
DWord of transfer state, and a five-element array of data buffer pointers. This structure
is 32 bytes (or one 32-byte cache line). This data structure must be physically
contiguous.
The buffer associated with this transfer must be virtually contiguous. The buffer may
start on any byte boundary. A separate buffer pointer list element must be used for
each physical page in the buffer, regardless of whether the buffer is physically
contiguous.
Host controller updates (host controller writes) to stand-alone qTDs only occur during
transfer retirement. References in the following bit field definitions of updates to the
qTD are to the qTD portion of a queue head.
Figure 49.

Queue Element Transfer Descriptor Block Diagram

Queue Element Transfer Descriptors must be aligned on 32-byte boundaries.
August 2006
Order Number: 306262--, Revision: 004US
® ®
IXP45X and Intel IXP46X Product Line of Network Processors
siTD Back Pointer. This field is a physical memory pointer to a siTD.
(Reserved). This field is reserved for future use. It should be zero.
Terminate (T).
0 = siTD Back Pointer field is valid.
1 = siTD Back Pointer field is not valid.
Intel
Description
® ®
IXP45X and Intel IXP46X Product Line of Network Processors
B4466-01
Developer's Manual
399