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Architecture
2.2
Open Host Controller Interface Functionality
2.2.1
OHCI Controller Overview
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 control 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 USB1.1 host controller provides.
The OHCI Specification for USB focuses on two main aspects of the USB host controller hardware
implementation: its register set and the memory data structures that define the appearance of USB bus
activity. Other topics include interrupt generation, USB host controller state, USB frame management, and
the hardware methods used 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. USB1.1 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.
2.3
Differences From OHCI Specification for USB
The USB1.1 module OHCI compatible 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 the pin multiplexing options.
2.3.1
Power Switching Output Pins Not Supported
The device does not provide pins that can be controlled directly by the USB1.1 host controller OHCI port
power control features. The OHCI RHPORTSTATUS register port power control bits can be programmed
by the USB1.1 host controller driver software, but this does not have any direct effect on any VBUS
switching implemented on the board.
You can use software control of GPIO pins or other implementation-specific control mechanisms to control
VBUS switching.
2.3.2
Overcurrent Protection Input Pins Not Supported
The device does not provide any pins that allow the USB1.1 host controller OHCI RHPORTSTATUS
overcurrent protection status bits to be directly controlled by external hardware.
You can use software monitoring of GPIO pins or other implementation-specific control mechanisms to
report port overcurrent information to the USB1.1 host controller driver.
2.3.3
No Ownership Change Interrupt
The USB1.1 host controller does not implement the OHCI ownership change interrupt.
10
Universal Serial Bus OHCI Host Controller
www.ti.com
SPRUFM8 – June 2009
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