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Zynq-7000 AP SoC Technical Reference Manual www.xilinx.com 442
UG585 (v1.11) September 27, 2016
Chapter 15: USB Host, Device, and OTG Controller
The asynchronous list is a simple circular list of queue heads that are aligned on 32-byte address
boundaries. The usb.ASYNCLISTADDR_ [31:5] bit field is a pointer to the next queue head. This bit
field is initialized by software. Hardware uses this field to traverse the Asynchronous schedule.
Hardware does not modify this field. The Asynchronous schedule implements a pure round-robin
service for the queue heads. Each queue head has one or more transfer descriptors (qTD’s). The
number of queue heads in the circular can be added to and reduced. The number of QH’s is not
limited by the EHCI specification.
15.11 EHCI Implementation
The host controller utilizes the programming mode of the Intel EHCI 1.0 specification. This includes
register models and host functionality.
15.11.1 Overview
The host controller operational mode is nearly compatible with the EHCI 1.0 specification. There are
a few differences and enhancements to handle an FS/LS link:
Embedded Transaction Translator
•EHCI Reserved Bits
•No PCI registers
SOF Interrupt
X-Ref Target - Figure 15-16
Figure 15-16: USB Host Controller Asynchronous Schedule Organization
UG585_c15_44_030713
Queue Head 0
Aysnchronous Queue Heads
(Bulk and Control)
Queue Head 2
Round Robin Priority.
QHs are processed as
Bandwidth allows.
Insert and Remove QH’s as needed
Queue Head 1
usb.ASYNCLISTADDR_ [31:05]
Asynchronous QH
Address Pointer
(32-bit system address)
00000
Queue Head n
Start of List
End of List