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Zynq-7000 AP SoC Technical Reference Manual www.xilinx.com 450
UG585 (v1.11) September 27, 2016
Chapter 15: USB Host, Device, and OTG Controller
15.12 Host Data Structures Reference
These descriptor data structures are compatible with the EHCI specification with some differences as
noted in section 15.11 EHCI Implementation.
The data structures defined in this section are (from the host controller's perspective) a mix of
read-only and read/writable fields. The host controller preserves the read-only fields.
Section Content
15.12.1 Descriptor Usage
15.12.2 Transfer Descriptor Type (TYP) Field
15.12.3 Isochronous (High Speed) Transfer Descriptor (iTD)
15.12.4 Split Transaction Isochronous Transfer Descriptor (siTD)
15.12.5 Queue Element Transfer Descriptor (qTD)
15.12.6 Queue Head (QH)
15.12.7 Transfer Overlay Area
15.12.8 Periodic Frame Span Traversal Node (FSTN)
15.12.1 Descriptor Usage
15.12.2 Transfer Descriptor Type (TYP) Field
The Transaction Type bit field is defined and used in the situations listed in Table 15-24.
Table 15-23: USB Host Descriptor Usage
Descriptors
Periodic Frame List Asynchronous List
Isochronous Interrupt Bulk Control
iTD, siTD yes no no
QH, qTD no yes yes yes
FSTN (Low-, Full-speed) no yes
Table 15-24: USB Host Transfer Descriptor Type (TYP) Bit Field
Data Structure
iTD
00
QH
01
siTD
10
FSTN
11
Description
Periodic Frame List
XXXX
Figure 15-15 USB Host Periodic Schedule with Example
iTD
X~~~
Table 15-25 USB Host Isochronous Transfer Descriptor
(iTD) Format
siTD
~X~~
Table 15-29 USB Host Split-Transaction Isochronous
Descriptor (siTD) Format