Tandem Computers Incorporated

Shannon J Lynch

Robert W Horst

Robert L Jardine

Philip R Manela

Cirillo L Costantino

John M Beirne

A system for issuing a family of instructions during a single clock includes a decoder for decoding the family of instructions and logic, responsive to the decode result, for determining whether resource conflicts would occur if the family were issued during one clock. If no resource conflicts occur, an execution unit executes the family regardless of whether dependencies among the instructions in the family exist.

Computer architecture capable of concurrent issuance and execution of

A mechanism for handling exceptions in a processor system that issues a family of more than one instruction during a single clock that utilizes the exception handling procedures developed for single instructions. The mechanism detects an exception associated with one of the instructions in the family, inhibits the data writes for the instructions in the family, flushes the pipeline, and reissues the instruction singly. The exception handling procedure for the single instruction may then be utilized.

Paired instruction processor precise exception handling mechanism

A branch recovery mechanism completes the processing of a concurrently issued family of instructions depending on the location of the branch instruction in the family and on whether the branch was correctly predicted. If the branch was not correctly predicted, the writes and stores of instructions in the family the precede the branch instruction are completed and those instructions are retired. However, the writes and stores of the instructions in the family following the branch instruction are inhibited.

Method and apparatus for recovering from an incorrect branch prediction

The various functional units which comprise a central processing unit of a computer are organized so as to enable a main arithmetic logic unit and special function units including an auxilliary arithmetic logic unit to access data registers, literal constants, and data from a memory cache. A general purpose bus closely couples the functional units to the main data paths and allows the CPU sequencer to branch on numerous conditions which may be indicated via test lines. Parity from the functional units is sent to clock cycle later than results in order that the parity path does not affect machine cycle time. The architecture allows unused microcode options to be used to check for correct CPU operation by halting CPU operation on a miscompare of two buses.

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Los Altos, CA, United States of America

Shannon J Lynch