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REF: BB_SRM_xM BeagleBoard-xM System

Reference Manual

Revision A2

Page 72 of 164

8.12.3 McBSP_CLKS

An additional clock is also provided by the TPS65950 called McBSP_CLKS. This clock

is provided to the PROCESSOR in order to insure synchronization of the I2S interface

between the processor and the TPS65950.

8.13 USB OTG Port

The BeagleBoard has a USB OTG (On-the-Go) port. It can be used as an OTG port,

Client port, or Host port. The main use is as a client port, as that is the mode that will

supply the power needed to power the BeagleBoard. With the addition of the USB Host

ports, the need to use three OTG port as a Host, is not really needed.

8.13.1 USB OTG Overview

USB OTG is a supplement to the USB 2.0 specification. The standard USB uses a

master/slave architecture, a USB host acting as a master and a USB peripheral acting as a

slave. Only the USB host can schedule the configuration and data transfers over the link.

The USB peripherals cannot initiate data transfers, they only respond to instructions

given by a host.

USB OTG works differently in that gadgets don't need to be pure peripherals because

they can sometimes act as hosts. An example might be connecting a USB keyboard or

printer to BeagleBoard or a USB printer that knows how to grab documents from certain

peripherals and print them. The USB OTG compatible devices are able to initiate the

session, control the connection and exchange Host/Peripheral roles between each other.

The USB OTG supplement does not prevent the use of a hub, but it describes role

swapping only in the case of a one-to-one connection where two OTG devices are

directly connected. If a standard hub is used, the supplement notes that using it will lead

to losing USB OTG role-swap capabilities making one device as the Default-Host and the

other as the Default-Peripheral until the hub is disconnected.

The combination of the processor and the TPS65950 allows the BeagleBoard to work as

an OTG device if desired. The primary mode of operation however, is intended to be a

client mode in order to pull power from the USB host which is typically a PC. As the Rev

B does not have a Host USB port, this port will be used as a Host port in many

applications.

NOTE: In order to use the OTG in the Host mode, the

leBoard must be

owered

rom the DC su

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