Queue Element Transfer Descriptor (Qtd) - Freescale Semiconductor MPC8313E Family Reference Manual

Universal Serial Bus Interface
Bits Name
4–1 —
0 T
16.5.5

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 20,480 (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 16-40 shows the queue element transfer descriptors.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
1
dt Total Bytes to Transfer
Buffer Pointer (Page 0)
Buffer Pointer (Page 1)
Buffer Pointer (Page 2)
Buffer Pointer (Page 3)
Buffer Pointer (Page 4)
1
Host controller read/write; all others read-only.
Queue element transfer descriptors must be aligned on 32-byte boundaries.
MPC8313E PowerQUICC II Pro Integrated Processor Family Reference Manual, Rev. 3
16-58
Table 16-52. siTD Back Link Pointer (continued)
Reserved, should be cleared. This field is reserved for future use. It should be cleared.
Terminate
0 siTD Back Pointer field is valid
1 siTD Back Pointer field is not valid
Next qTD Pointer
Alternate Next qTD Pointer
1
Figure 16-40. Queue Element Transfer Descriptor (qTD)
Description
15 14 13 12 11 10 9
PID
1 1
ioc C_Page Cerr
Code
8 7 6 5 4 3 2 1
0000
0000
1
Status
1
Current Offset
0000_0000_0000
0000_0000_0000
0000_0000_0000
0000_0000_0000
Freescale Semiconductor
0 offset
T 0x00
T 0x04
0x08
0x0C
0x10
0x14
0x18
0x1C