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X-Ref Target - Figure 15-20<br />

31<br />

DT<br />

30 29<br />

28 27 26 25 24 23 22 21 20 19 18<br />

Total Bytes<br />

Host Controller Read/Write<br />

Next qTD Pointer<br />

Alternate Next qTD Pointer<br />

Chapter 15: USB Host, Device, and OTG Controllers<br />

Queue Element Transfer Descriptors must be aligned on 32-byte boundaries.<br />

15.10.14 Next qTD Pointer<br />

17 16 15 14 13 12 11 10 9 8 7 6 5 4<br />

Buffer Pointer (Page 0) Current Offset<br />

Buffer Pointer (Page 1)<br />

Buffer Pointer (Page 2)<br />

Buffer Pointer (Page 3)<br />

Buffer Pointer (Page 4)<br />

C_Page Cerr PID Status<br />

Reserved<br />

Reserved<br />

Reserved<br />

Reserved<br />

Figure 15‐20: Queue Element Transfer Descriptor Block Diagram<br />

3 2 1 0<br />

0 T<br />

0 T<br />

UG585_c15_20_030312<br />

The first DWORD of an element transfer descriptor is a pointer to another transfer element<br />

descriptor.<br />

Table 15‐30: qTD Next Element Transfer Pointer (DWORD 0)<br />

Bits Description<br />

IOC<br />

Host Controller Read Only<br />

31:5 Next Transfer Element Pointer (Next qTD Pointer)<br />

This field contains the physical memory address of the next qTD to be processed. The<br />

field corresponds to memory address signals[31:5], respectively.<br />

4:1 Reserved<br />

Field reserved and should be set to zero.<br />

0 Terminate bit (T).<br />

• 1b: Pointer is not valid<br />

• 0b: Pointer is valid (points to a valid Transfer Element<br />

This bit indicates to the Host controller that there are no more valid entries in the<br />

queue.<br />

<strong>Zynq</strong>‐<strong>7000</strong> EPP Technical Reference Manual www.xilinx.com 355<br />

UG585 (v1.2) August 8, 2012<br />

03-00h<br />

07-04h<br />

0B-08h<br />

0F-0Ch<br />

13-10h<br />

17-14h<br />

1B-18h<br />

1F-1Ch

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