Processor transparent on-the-fly instruction stream...

Details Processor transparent on-the-fly instruction stream... Processor transparent on-the-fly instruction stream...

1997-09-23

2001-03-06

Lee, Thomas C. (Department: 2787)

Electrical computers and digital data processing systems: input/

Input/output data processing

Peripheral adapting

Reexamination Certificate

active

06199126

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a circuit and method for transparent on-the-fly decompression of the program instruction stream of a processor.
BACKGROUND OF THE INVENTION
With computer processors getting smaller and cheaper, and computer programs getting larger and more complex, the size and cost of a computer's memory for storing program information has become a significant portion of the cost of a computer solution. While memory cost is important in general purpose computer systems, such as personal computers, it becomes critical in embedded special-purpose computer devices, especially those used in low-cost products. Significant cost reductions in computer-based products may be realized by reducing the memory required by a particular program. One possible technique involves compressing the program instructions in memory.
In order to use compressed programs, program instructions within the memory may be grouped into blocks and each block compressed by techniques well known in the art. For example, see “Elements of Information Theory, T. Cover & T. Thomas, Wiley & Sons, New York (1991). In the prior art, whenever processor
102
, shown in
FIG. 1
, wishes to execute the instructions in a particular block, other program instructions are executed that read the block from memory, decompress it and temporarily store it while the instructions are executed.
This solution has several problems. It involves a serious performance penalty. Furthermore, it requires modifications to be made to the computer system. In particular, the tools used to program the processor, such as, compilers, linkers, editors and debuggers, must be modified. The problem with this is the high cost of recreating the tools for the new computer software structure. A need arises for a technique that allows a computer program to occupy less space, while allowing the changes to the program to be transparent to the computer and its supporting tools.
SUMMARY OF THE INVENTION
The present invention is an apparatus and method for transparent on-the-fly decompression of the program instruction stream of a processor. It allows a computer program to occupy less space, while allowing the changes which were made to the program to be transparent to the computer and its supporting tools.
Connected between a processor and a memory storing compressed information is a decompression device. The decompression device, receives a request from the processor for information, retrieves compressed information from the memory, decompresses the retrieved compressed information to form uncompressed information, and transmits the uncompressed information to the processor. The compressed information may include both program instructions and data.
When the decompression device receives a request for information, which includes an unmodified address, from the processor, it generates an index offset from the received unmodified address. An indexed address corresponding to the generated index offset is retrieved from an index table. Compressed information corresponding to the selected indexed address is retrieved from the memory and transmitted to the decompression device, where it is decompressed and set to the processor. Thus, the entire decompression operation is transparent to the processor.


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