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System for maintaining a minimum level of digitized data signal quality while allowing bandwidth dependent quality enhancement with additional enhancement data packets
RELATED APPLICATIONS
This application is related to the copending application \Data Rate Adjustment To Maintain Throughput Of A Time Varying Signal\Ser. No. 08/667,072 filed Apr. 18, 1996, now pending. FIELD OF THE INVENTION
The present invention pertains to the field of the transfer of data over a bus. More specifically, the present invention relates to
methods of transferring an assured minimum level of data supplemented by quality improvements. BACKGROUND
Digital systems continue to process escalating quantities of signals representing video, audio, and other time varying phenomena over limited bandwidth communication channels. Typically, such time
varying signals are transferred via at least one shared signal line or processed by a component which also handles signals from multiple devices. The various signal sources must compete in an environment where bandwidth is a precious commodity.
Consequently, sustaining communication of a time varying signal over the shared signal line(s) to a processing system often requires a compromise between bandwidth sharing and signal quality. That is, either the peak signal quality suffers in order to preserve adequate bandwidth for other devices, or the time varying signal unduly monopolizes the available bandwidth.
One instance where this problem arises is in transferring a
continuous natural data type (i.e. motion video and/or audio) over a
bus in a computer system. Transferring motion video from a video peripheral device to a system memory requires periodic access to the bus which couples the memory to the peripheral. Depending on the desired quality level of the motion video, a substantial portion of the total bus bandwidth may be consumed by the video transfer. At times, this motion video transfer can have a deleterious effect on the performance of other devices which seek access to the bus. At other times, a portion of the available bus bandwidth may remain unused.
In some prior art systems, other devices must simply wait for access to the bus, relying on the user or the system designer to consider whether the system can adequately accommodate all bus accesses. If the bus is over-utilized, and the other devices have limited
buffering capabilities or require real time access, data may be lost. Even if there is no data loss, bus over-utilization may cause noticeably increased latencies for bus transactions such as input device response or network access.
Some prior art protocols, through the use of interrupt signals or other urgent bus request signals, allow a device to quickly seize bus domination from a monopolistic bus agent such as a video peripheral. These interruptions, however, often have no particular known latency or bandwidth. Thus, the video peripheral does not respond by
adjusting the bandwidth it seeks to obtain. As a result, the video transfer may be abruptly altered and the video quality degraded to an unacceptable level.
Other prior art bus protocols provide a guaranteed bandwidth dedicated to a certain device. One example is the isochronous transfer mode of the universal serial bus (USB), discussed in the Universal Serial Bus Specification Revision 1.0, Jan. 16, 1996, available from Intel Corporation of Santa Clara, Calif. The USB protocols also provide a bulk transfer mode which fills in unused bandwidth but does not guarantee any particular data transfer rate. Unfortunately, the bulk transfer mode cannot guarantee a minimum data throughput, and the isochronous transfer mode provides only a fixed bandwidth regardless of bus utilization.
Thus, prior signal transfer techniques tend to monopolize the bus, sacrifice peak quality, or fail to guarantee a minimum quality signal transfer. These prior art systems do not adequately address the need to obtain the best possible signal quality over signal lines with fluctuating loads because they do not transfer signals at a
guaranteed minimum quality level enhanced by quality improvement transfers as bandwidth availability permits. SUMMARY
A method and apparatus for transferring data representing a continuous natural data type over at least one signal line is described. In accordance with the described method, signal data
packets representing the continuous natural data type are requested. Enhancement data packets providing an improved quality level are also requested. After the receipt of a plurality of signal packets
representing a discrete segment of the continuous natural data type is detected, the plurality of signal data packets and a plurality of enhancement data packets are combined to reconstruct a received version of the continuous natural data type.
A system of the present invention includes a processor coupled to a controller by a processor bus. A signal source coupled to the
controller provides digital values representing a time varying signal. A memory coupled to the processor and the controller contains a data request routine for requesting data from fixed and variable bandwidth channels and a receiving routine for receiving signal packets from the fixed bandwidth channel and enhancement packets from the variable bandwidth channel. The memory also contains a reconstruction routine for combining the signal packets and the enhancement packets to form a reconstructed signal. BRIEF DESCRIPTION OF THE FIGURES
The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings. FIG. 1 is a flowchart illustrating one method of the present invention.
FIG. 2 illustrates a system which performs video processing according to the present invention.
FIG. 3 is a flowchart illustrating one method of the present invention used for video processing in the system of FIG. 2. DETAILED DESCRIPTION
The present invention provides a method and apparatus for maintaining a minimum level of data quality while allowing bandwidth-dependent