Browse Prior Art Database

Data Line Pulsing Mechanism for USBOTG Session Request Protocol

IP.com Disclosure Number: IPCOM000031771D
Original Publication Date: 2004-Oct-08
Included in the Prior Art Database: 2004-Oct-08
Document File: 3 page(s) / 41K

Publishing Venue

Motorola

Related People

Arnaldo R. Cruz: AUTHOR [+2]

Abstract

The USB-OTG allows USB device to device communications without the use of a PC. The session request protocol (SRP) is used to establish this logical connection, and the implementation of SRP may impose some software real time requirements that may be difficult to achieve in some systems. This paper describes an implementation that avoids this problem.

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Data Line Pulsing Mechanism for USBOTG Session Request Protocol

Arnaldo R. Cruz

Darren Weninger

Abstract

The USB-OTG allows USB device to device communications without the use of a PC. The session request protocol (SRP) is used to establish this logical connection, and the implementation of SRP may impose some software real time requirements that may be difficult to achieve in some systems. This paper describes an implementation that avoids this problem.

The Universal Serial Bus (USB) is an industry standard originally designed for personal computers as a low cost mechanism for adding peripherals. Because of its popularity and flexibility its use has been extended beyond the traditional use in personal computers and peripherals, and now is also used for consumer devices, such as digital cameras and mobile devices such as cellular phones. The USB bus was designed as a PC centric system, where the PC takes the role of the bus master initiating and controlling all transfers. In this framework, USB peripherals must be connected to a PC for data transfers. For mobile applications it is desirable that devices communicate directly with each other without the use of a computer. For example, a USB color printer could be connected to a cellular camera phone to print some pictures, or a USB hard disk could be connected to a PDA to transfer several files. The USB On-The-Go (OTG) supplement was added to the USB 2.0 specification for this type of applications. This addendum defines a protocol for OTG devices to establish communication and designate host and device roles during a session.

            USB-OTG devices use a mini-AB receptacle, which can accept both mini-A USB plug or  mini-B USB plugs. The USB-OTG cable has a mini-A plug and a mini-B plug, the device connected to the A plug is referred to as the USB-A device, the device connected to the mini-B plug is referred to as the USB-B device. USB OTG uses the session request protocol (SRP) to establish a session (connection) between two USB devices. One of the mechanisms used for SRP is data line pulsing...