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Zynq-7000 AP SoC Technical Reference Manual www.xilinx.com 444
UG585 (v1.11) September 27, 2016
Chapter 15: USB Host, Device, and OTG Controller
15.11.2 Embedded Transaction Translator
The host controller emulates one transaction translator (TT) with up to 16 periodic (Iso/Int) contexts
and 2 asynchronous (bulk/ctrl) contexts. The TT allows FS/LS devices to be attached directly to the
controller in host mode without the need for hardware to implement a companion controller.
The transaction translator is modeled as an extension to EHCI specification by making use of the
standard data structures and operational models that exist in the EHCI specification. The TT is
responsible for:
All error checking
Field generation checking
Formatting of all the necessary handshake actions
Ping and data response packets on the bus
For any signal that must be generated based on a USB based time in the host controller, the protocol
engine also generates all of the token packets required by the USB protocol.
There is no separate transaction translator hardware to handle FS/LS protocols. The transaction
translator function implemented within the DMA and the protocol engine blocks to support direct
connection to LS and FS devices.