BACKGROUND OF THE INVENTION

The present invention is a development of the microcomputer described in our European patent specification No. 0113516. That specification describes the microcomputer with a memory and processor arranged to execute a plurality of concurrent processes and to provide synchronised communication between concurrent processes on the same microcomputer or interconnected microcomputers. However, the device described in that specification was arranged to transmit messages which were each of one word length. After execution of each message instruction one word is transmitted and subsequent message instructions are required in order to cause further words to be transmitted. In the case of a 16 bit machine each message would be of 16 data bits.

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a simplified, reduced instruction set computer (RISC) microprocessor. More particularly, it relates to such a microprocessor which is capable of performance levels of, for example, 20 million instructions per second (MIPS) at a price of, for example, 20 dollars.

2. Description of the Prior Art

Since the invention of the microprocessor, improvements in its design have taken two different approaches. In the first approach, a brute force gain in performance has been achieved through the provision of greater numbers of faster transistors in the microprocessor integrated circuit and an instruction set of increased complexity. This approach is exemplified by the Motorola 68000 and Intel 80X86 microprocessor families. The trend in this approach is to larger die sizes and packages, with hundreds of pinouts.

More recently, it has been perceived that performance gains can be achieved through comparative simplicity, both in the microprocessor integrated circuit itself and in its instruction set. This second approach provides RISC microprocessors, and is exemplified by the Sun SPARC and the Intel 8960 microprocessors. However, even with this approach as conventionally practiced, the packages for the microprocessor are large, in order to accommodate the large number of pinouts that continue to be employed. A need therefore remains for further simplification of high performance microprocessors.

With conventional high performance microprocessors, fast static memories are required for direct connection to the microprocessors in order to allow memory accesses that are fast enough to keep up with the microprocessors. Slower dynamic random access memories (DRAMs) are used with such microprocessors only in a hierarchical memory arrangement, with the static memories acting as a buffer between the microprocessors and the DRAMs. The necessity to use static memories increases cost of the resulting systems.

Conventional microprocessors provide direct memory accesses (DMA) for system peripheral units through DMA controllers, which may be located on the microprocessor integrated circuit, or provided separately. Such DMA controllers can provide routine handling of DMA requests and responses, but some processing by the main central processing unit (CPU) of the microprocessor is required.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide a microprocessor with a reduced pin count and cost compared to conventional microprocessors.

It is another object of the invention to provide a high performance microprocessor that can be directly connected to DRAMs without sacrificing microprocessor speed.

It is a further object of the invention to provide a high performance microprocessor in which DMA does not require use of the main CPU during DMA requests and responses and which provides very rapid DMA response with predictable response times.

The attainment of these and related objects may be achieved through use of the novel high performance, low cost microprocessor herein disclosed. The microprocessor integrated circuit includes a processing unit disposed upon an integrated circuit substrate. In a preferred implementation the processing unit operates in accordance with a predefined sequence of program instructions stored within an instruction register. A memory, capable of storing information provided by the processing unit and occupying a larger area of the integrated circuit substrate than the processing unit, is also provided within the microprocessor integrated circuit. The memory may be implemented using, for example, dynamic or static random-access memory.

The attainment of the foregoing and related objects, advantages and features of the invention should be more readily apparent to those skilled in the art, after review of the following more detailed description of the invention, taken together with the drawings, in which:

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