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Multiplexing Scheme for Application Processor

IP.com Disclosure Number: IPCOM000004712D
Original Publication Date: 2001-Apr-17
Included in the Prior Art Database: 2001-Apr-17
Document File: 3 page(s) / 62K

Publishing Venue

Motorola

Related People

Bill Gabehart: AUTHOR [+3]

Abstract

Multiplexing Scheme for Application Processor

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This is the abbreviated version, containing approximately 67% of the total text.

Multiplexing Scheme for Application Processor

Bill Gabehart, Reginald Richardson, Carl Wojewoda

BACKGROUND

Smart phones are being designed to be data-centric and are required to support more features. These products will have both USB Host and Function capability and will need to interface to both USB Function and USB Host accessories respectively. Current phone platforms only have USB Function (Slave) capability. This means that the USB Accessory is the Host (Master). A Multiplexing circuit can be used to allow the application processor to act as the USB Host or USB Function.

PROBLEM

Earlier phone designs were powered by a single processor, which handled call processing (base band) and the user interface. In new smart phones, the base band processor is no longer adequate to handle the call processing and the complex PDA features.

A second processor, the Application processor, is required to handle the user interface and user applications. This Application processor must be able to communicate with the Base band processor and the accessory connector via a high data speed link. An example application would be a phone hooked to a laptop acting as a high-speed wireless modem on a 3G network. A USB link can be used for a high-speed link between the Application and Base band processors and from the Application processor to the Accessory connector. This USB link can also serve as the messaging link between the processors for other purposes.

A multiplexing circuit needs to allow the Application processor to communicate to the Base band processor and Accessory connector via USB. The Application processor should have the ability to act as the USB Master or Slave to the accessory. The Multiplexing circuit should also allow a direct path to the Baseband processor for Flash programming and testing purposes.

SOLUTION

The Proposed implementation of the USB master and slave functions on the Application Processor (AP) includes two multiplexers and a Serial Audio Port (SAP) interface1. (Figure 1 below) The AP Host Controller, for these diagrams, is shown with 4 ports, HP1 through HP4.

Multiplexer 1 allows the Baseband Processor to communicate to the USB Host on the application processor or directly to the Accessory Connector via MUX2. This will allow the Baseband processor to be programmed directly from the accessory connector. The Application Processor can be programmed into the USB pass through mode via the JTAG interface. JTAG is a common interface used for testing and debugging purposes, and using the JTAG interface avoids adding another pin to the circuit. The JTAG command would set a register in the Application Processor, which then sets the path of the Multiplexers.

Multiplexer 2 allows the Accessory Connector to communicate with the Baseband processor as just discussed, or to the USB Function Controller, USB Host Controller (HP1), or the UART on the Application processor.

Therefore, the AP can communicate with accessories that are either

1. RS232 serial ports

2. USB ma...