MCIMX27 Datasheet, PDF (1070/1650 Pages) Freescale Semiconductor, Inc – Multimedia Applications Processor

High-Speed USB On-The-Go (HS USB-OTG)
30.8.2.5 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.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Next qTD Pointer
0 T 03-0
Alternate Next qTD Pointer
0 T 07-0
dt
Total Bytes to Transfer
io C_Page Cerr PI
Status
0B-0
Buffer Pointer (page 0)
Current Offset
0F-0
Buffer Pointer (page 0)
Reserved
13-1
Buffer Pointer (page 0)
Reserved
17-1
Buffer Pointer (page 0)
Reserved
1B-1
Buffer Pointer (page 0)
Reserved
1F-1
Host Controller Read/Write
Host Controller Read Only.
Figure 30-47. Queue Element Transfer Descriptor Block Diagram
Queue Element Transfer Descriptors must be aligned on 32-byte boundaries.
30.8.2.5.1 Next qTD Pointer
The first DWord of an element transfer descriptor is a pointer to another transfer element descriptor.
30-88
MCIMX27 Multimedia Applications Processor Reference Manual, Rev. 0.2
Freescale Semiconductor