Bull Hn Information Systems, Inc.

Steven S Smith

Thomas F Joyce

Richard P Brown

Arnold J Smith

Amy E Gilfeather

The emulator includes first and second pipelined stages connected through a bidirectional bus for executing source instructions normally executed by a different/source computer in a highly overlapped manner. The first stage includes an emulator chip which performs the function of fetching and decoding each source instruction stored in cache memory resulting in the generation of a number of vector addresses required for executing the instruction by the second stage. The second stage includes a high performance microprocessor chip having on-chip instruction and data caches for storing a plurality of emulation subroutines and data fetched during subroutine execution. In pipelined fashion, the emulator chip fetches and decodes each source instruction which generates a vector branch address which is loaded into the branch vector register while the microprocessor chip fetches and executes emulation subroutines specified by the vector address transferred via the bus for each previously decoded source instruction.

Emulation of CISC instructions by RISC instructions using two pipelined

A system includes first and second processing units which are interconnected by a bidirectional bus. The first processing unit is a microprocessor chip programmed for executing procedures stored in an on-chip instruction cache unit. The second processing unit receives requests from an external source such as a system bus. The microprocessor chip includes a branch vector facility which connects to the bus. The second processing unit in response to an external request, generates a vector branch address. The processing unit transfers the vector branch address to the branch vector facility for storage along with setting a write indicator. The microprocessor chip, upon detecting that the write indicator was set, branches to the procedure specified by the branch vector address for executing the instructions of the procedure to carry out those operations required for processing the external request or event.

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Nashua, NH, United States of America

Steven S Smith