Parallel to serial asynchronous hardware assisted DSP interface

Details Parallel to serial asynchronous hardware assisted DSP interface Parallel to serial asynchronous hardware assisted DSP interface

1999-05-28

2002-04-23

Lee, Thomas (Department: 2782)

Electrical computers and digital data processing systems: input/

Input/output data processing

Peripheral adapting

C710S070000, C379S056200, C379S093240

Reexamination Certificate

active

06378011

ABSTRACT:

BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to the field of modem serial port communications, between a host computer modem and various mobile communication devices. More specifically the invention relates to a parallel to serial asynchronous hardware assisted DSP interface, as used in modem communication across digital or AMPS cellular networks, high speed digital telephone lines, and other wireless communication networks.
2. The Relevant Technology
The extensive development of powerful portable personal computers, low cost high speed modems, and digital cellular telephones, creates the infrastructure required for a convenient and efficient mobile data communication network. Unfortunately, one of the main obstacles to creating this type of mobile data communication network is the difficulty of integrating each of these components.
Mobile network designers continue to be burdened by communication standards established years ago for what was then three configurations. For example, modems of the kind used with portable personal computers are generally not intended to physically and electrically interface with digital cellular telephone networks, instead hardware interfaces and connectors focus on land based analog telephone networks. While some solutions to the compatibility and integration problems exist, each configuration contains defects that make the specific implementation either commercially prohibitive or impractical.
One configuration is to integrate the digital modem and digital cellular telephone into one unit, thereby creating a wireless modem with an integrated digital cellular transceiver. This configuration is undesirable for several reasons. First, the hardware necessary for digital cellular communication is expensive. Second, a user will generally need both a digital cellular modem and a digital cellular telephone. This configuration requires the user to carry expensive duplicate digital communication hardware around, not to mention the duplicate monthly digital phone service fee.
A second configuration uses a customized data interface on a digital cellular telephone that slows down the reception and transmittal of data to and from the personal computer. One problem with this configuration is that it does not take advantage of the high speed data transfer rates that are possible with a digital cellular phone. Instead, communication rates are limited to the traditional slower transfer rates associated with analog cellular phone lines. An additional problem with this configuration is that the customized data interface requires either special software, hardware, or both to operate effectively. This type of interface will often require a special digitally compatible modem to communicate with the digital cellular interface. This non-standard software and hardware requirement hampers the ability of the computer to run many common communication software programs that utilize a proprietary protocol or require standard serial connections but provide their own drivers. A useful example is the software necessary to connect with many Internet online services.
Another unacceptable configuration is to provide a hardware interface in a separate physical package from the modem. This interface simulates a standard RJ 11 telephone jack to the conventional modem and connects on the other side to the data input/output of a digital cellular telephone. The main disadvantage of this configuration is the need for additional hardware to be carried with the computer and added whenever a digital communications link is to be established. A secondary disadvantage is the drain placed on the battery of the laptop computer, the hardware interface, or the cellular telephone by the generation of high voltage signals required for the input to the modem, like the ring signal. Finally, the modem signal may be degraded through the hardware interface connections resulting in a potential loss of data before the information even gets onto the digital cellular network.
The invention of faster communication technology actually amplify these old throughput problem areas. The Universal Asynchronous Receiver Transmitter (UART) has long been accused of slowing down the serial communication data pipeline. Traditionally, cellular communication rates were limited by the serial nature of the analog cellular phone or the Advanced Mobile Phone Service (AMPS) cellular phone. Fortunately, the UART interface was barely sufficient to satisfy the transfer rate requirements of the modem. But increasing the speed of transmission and reception network only amplify the UART problems. With the advent of digital cellular telephones, transmission speeds exceed the capabilities of the standard UART. In fact the UART is being stressed on both sides as the V.90 protocol further enhances the modem's expected communication rate with the host computer.
Presently, there are two main improvements which are applying stress to the modem-to-digital phone network interface. First, the data communication rates of digital modems have increased substantially over previous levels. Second, the possible transmission rate across a digital cellular network is substantially higher than across the analog cellular network. Because the interface remains the same, it becomes the bottleneck between the DSP and the network. The result is that the digital modem DSP is able to quickly transfer data to the interface, but must either process each byte serially at substantial overhead or wait for the interface to complete serialization before the data can be transmitted across the cellular line. Often the overhead to the DSP can cause the user to notice system performance degradation while the DSP is stalling to send or receive the next byte.
Cellular modems must communicate with the cellular phone via a proprietary protocol established by the cellular manufacturer. In the case of the AMPS cellular standard, the communication is traditionally a low rate serial communication for control, and analog for data to be transmitted. These low rates are achieved by the DSP via a General Purpose Input Output (GPIO) port, but at a significant DSP overhead cost. Newer digital phones have higher rate communication interfaces that combine control and data, such that the DSP overhead at these rates would use too many DSP resources. What is needed in high speed digital cellular digital communication is an interface which allows the UART to function at a very high throughput level, while at the same time minimizing the drain upon the digital signal processor and personal computer. These particular features should be implemented utilizing hardware as software would increase the overhead pressure on the DSP.
Traditionally, the modem would send an interrupt signal to the DSP. The DSP would then pass on an interrupt to the personal computer telling the computer that data was waiting for it to pick up. Due to the slow transfer rate, the computer could easily handle the interrupt and return to performing its previous program function without any noticeable delay to the user. With the new high speed transfers of smaller data blocks, the DSP is continually waiting for the computer to send more data, creating more interrupts and therefore interfering with the overall performance of the personal computer. Often these asynchronous data transfers become too cumbersome, requiring the DSP to virtually stop work on other projects until the data is processed. In essence the DSP is churning over the data blocks. This processor overhead drain is amplified when the device is connected to a cellular phone as the delays in verifying the quality of the data may cause the user of the personal computer, to notice a slowing in performing standard functions.
The dramatic increase in transmission capability has created a unique problem for modems trying to communicate across digital cellular networks. What is needed is an interface that can increase the throughput to an AMPS cellular or digital phone without increasing the overhead to the DSP. An impr

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