Usage Notes and Known Design Exceptions to Functional Specifications
Advisory 1.0.33
USB Host: USB Low-Speed Receive-to-Transmit Inter-Packet Delay
Revisions Affected
2.1, 2.0, 1.0
Details
The universal serial bus (USB) Specification Revision 2.0 requires that a host provide a
minimum of 2 bit-times of 'J' state between the single-ended zero (SE0) of an end-of-
packet (EOP) and the start of a new packet. While operating as a host in USB low-speed
mode, the AM335x device only provides a single bit-time of 'J' state after the SE0 of an
EOP that marks the end of a received packet.
The absence of the required minimum 2-bit time 'J' state as part of a USB low-speed
RX-to-TX bus transition can result in the failure of some low-speed peripheral devices to
function.
Peripherals connected at USB full-speed or high-speed to an AM335x operating in Host
mode are not affected by the issue described in this advisory.
Workarounds
None.
Advisory 1.0.34
USB2PHY: Register Accesses After a USB Subsystem Soft Reset May Lock Up the
Entire System
Revisions Affected
2.1, 2.0, 1.0
Details
The synchronization bridge connecting the USB2PHY register interface to the L3S
interconnect may hang and lock up the entire system. When there is a sequence of any
USB2PHY register access, followed by a USB subsystem soft reset initiated with the
SOFT_RESET bit in the SYSCONFIG register, followed by any USB2PHY register
access, the L3S interconnect may hang on the second USB2PHY register access.
Workarounds
Normal USB operation does not require any USB2PHY register changes. Therefore, one
solution for preventing this issue is never access any USB2PHY register.
If there is a requirement to access USB2PHY registers, the system software must
ensure there are no USB2PHY register access followed by a USB subsystem soft reset
followed by another USB2PHY register access.
36
SPRZ360F – October 2011 – Revised November 2013
Sitara™ AM335x ARM
®
Cortex™-A8 Microprocessors (MPUs) (Silicon
Revision 2.1, 2.0, 1.0)
Copyright © 2011–2013, Texas Instruments Incorporated
