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Zynq-7000 AP SoC Technical Reference Manual www.xilinx.com 473
UG585 (v1.11) September 27, 2016
Chapter 15: USB Host, Device, and OTG Controller
60 MHz PHY Clock
The external PHY provides a 60 MHz clock that the ULPI is syncd to and is used by the a majority of
the controller logic.
15.15.2 Reset Types
To reset the controller, software writes a 1 to the usb.USBCMD [RST] bit. When the reset process is
completed, the controller hardware sets this bit to 0. Once the reset is started, the controller cannot
stop the process. Writing a 0 has no effect.
When software writes a 1 to this bit, the Controller resets its internal pipelines, timers, counters, and
state machines to their initial value. Any transaction currently in progress on USB is immediately
terminated. A USB reset is not driven to downstream ports. Software should not set this bit to a 1
when the host controller halt bit, usb.USBSTS [HCH], = 0. Attempting to reset an actively running
host controller will result in undefined behavior.
Controller Resets
PS Reset System (full controller reset),
usb.USBCMD [RST] bit (partial controller reset useful for OTG).
OTG Mode Auto-Reset
ULPI PHY Reset
The USB controller does not have a reset output for the ULPI PHY. Instead, a PS or PL GPIO (or other
software controlled reset signal) must be connected to the PHY as shown in Figure 15-19, page 475.
USB Bus Reset
The host controller generates the standard USB reset as described in the EHCI specification. The
optional light host reset is not supported. The response by the device controller is described in
section 15.4.2 USB Bus Reset Response.
Summary of Resets
The controller has multiple reset sources and multiple reset domains. These are summarized in
Table 15-49 USB Resets Summary List.