Texas Instruments OMAP5912 Reference Manual page 1314

USB Host Controller
2.1 USB Open Host Controller Interface Functionality
2.1.1 OHCI Controller Overview
2.2 OMAP5912 USB Host Controller Differences From OHCI
Specification for USB
2.2.1 Power Switching Output Pins Not Supported
2.2.2 Overcurrent Protection Input Pins Not Supported
22 Universal Serial Bus (USB)
The Open HCI—Open Host Controller Interface Specification for USB,
Release 1.0a, defines a set of registers and data structures stored in system
memory that define how a USB host controller interfaces to system software.
This specification, in conjunction with the Universal Serial Bus Specification
Version 2.0, defines most of the USB functionality that the OMAP5912 USB
host controller provides.
The OHCI Specification for USB focuses on two main aspects of the hardware
implementation of a USB host controller: its register set and the memory data
structures that define the activity to appear on the USB bus. Also discussed
are issues such as interrupt generation, USB host controller state, USB frame
management, and the methods that the hardware must use to process the lists
of data structures in system memory.
This document does not duplicate the information presented in the OHCI
Specification for USB or the USB Specification. OMAP5912 USB host
controller users can refer to the USB Specification and the OHCI Specification
for USB for detailed discussions of USB requirements and OHCI controller
operation.
The OMAP5912 USB host controller implementation does not implement
every aspect of the functionality defined in the OHCI Specification for USB.
The differences focus on power switching, overcurrent reporting, and the
OHCI ownership change interrupt. Other restrictions are imposed by the
effects of OMAP5912 pin multiplexing options.
The OMAP5912 device does not provide pins that can be controlled directly
by the USB host controller OHCI port power control features. The OHCI
RHPORTSTATUS register port power control bits can be programmed by the
USB host controller driver software, but this does not have any direct effect on
any VBUS switching implemented on the board.
Users can use software control of GPIO pins or other implementation-specific
control mechanisms to control VBUS switching.
The OMAP5912 device does not provide any pins that allow the USB host
controller OHCI RHPORTSTATUS overcurrent protection status bits to be
directly controlled by external hardware.
SPRU761A