Digital data processing system including efficient arrangement t

Details Digital data processing system including efficient arrangement t Digital data processing system including efficient arrangement t

1997-05-30

1999-12-28

Follansbee, John A.

Electrical computers and digital processing systems: processing

Processing control

Branching

G06F 930

Patent

active

060095156

ABSTRACT:
A digital computer includes an efficient mechanism by which an exception handler can traverse the instruction stream in a reverse direction to identify the instruction which gave rise to the exception condition after a discontinuity in an instruction stream. The digital computer is provided with both a program counter and an "old program counter." For points in an instruction sequence at which a discontinuity may occur, the "branch taken" portion of the instruction stream is provided with a predetermined type of instruction to enable the old program counter to be saved in a predetermined location. When the instruction is executed, the old program counter will contain a pointer to the "branch not taken" portion of the instruction sequence. When an exception condition is detected during processing of an "excepting" instruction, when an exception handler is called to locate the excepting instruction, when the exception handler performs a reverse traversal operation of the instruction sequence to locate the excepting instruction, if it encounters a read old program counter instruction (which can occur if there was a discontinuity in the instruction sequence), it can determine the location of the "branch not taken" portion of the instruction sequence by referencing the saved old program counter contents in the location identified by the read old program counter instruction.

REFERENCES:
patent: 5095426 (1992-03-01), Senta
patent: 5109514 (1992-04-01), Garner et al.

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