Fujitsu Corporation

Hal Computer Systems, Inc.

Michael A Simone

Michael C Shebanow

John R Szeto

Gene W Shen

Niteen Aravind Patkar

Hideki Osone

Takumi Maruyama

John Gmuender

Deforest W Tovey

A method of permitting out of order execution of load instructions with respect to older store instructions in a general purpose computer evaluates whether the same data bytes are being accessed by both the store and load instructions and if they are not the same, then out of order execution of the load with respect to the store instructions is permitted.

Addressing method for executing load instructions out of order with

An instruction selector receives M instructions per clock cycle and stores N instructions in an instruction queue memory. An instruction queue generates a precedence matrix indicative of the age of the N instructions. A dependency checker determines the available registers for executing the instructions ready for execution. An oldest-instruction selector selects the M oldest instructions responsive to the precedence matrix and the eligible queue entry signals. The instruction queue provides the M selected instructions to execution units for execution. Upon completing the instructions, the execution units provide register availability signals to the dependency checker to release the registers used for the instructions.

Method and apparatus for selecting the oldest queued instructions

Time-out checkpoints are formed based on a predetermined time-out condition or interval since the last checkpoint was formed rather than forming a checkpoint to store current processor state based merely on decoded instruction attributes. Such time-out conditions may include the number of instructions issued or the number of clock cycles elapsed, for example. Time-out checkpointing limits the maximum number of instructions within a checkpoint boundary and bounds the time period for recovery from an exception condition. The processor can restore time-out based checkpointed state faster than an instruction decode based checkpoint technique in the event of an exception so long as the instruction window size is greater than the maximum number of instructions within a checkpoint boundary, and such method eliminates processor state restoration dependency on instruction window size. Time-out checkpoints may be implemented with conventional checkpoints, or in a novel logical and physical register rename map checkpointing technique. Timeout checkpoint formation may be used with conventional processor backup techniques as well as with a novel backtracking technique including processor backup and backstepping.

Processor structure and method for aggressively scheduling long latency

A method and apparatus for generating a zero flag (z-flag) status signal in a microprocessor includes a z-flag signal generator that generates a z-flag signal from unaligned data simultaneous to the load alignment of such data. The z-flag generator first performs a zero detect on each byte of data retrieved from memory. The zero detect results are next decoded according to bit selection signals generated from a data format code which corresponds to the specific format of the retrieved data.

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Sunnyvale, CA, United States of America

Michael A Simone