Electrical computers and digital processing systems: processing – Instruction issuing
Reexamination Certificate
1998-08-14
2001-01-23
An, Meng-Ai T. (Department: 2783)
Electrical computers and digital processing systems: processing
Instruction issuing
C712S221000, C712S224000, C709S241000
Reexamination Certificate
active
06178497
ABSTRACT:
TECHNICAL FIELD
The present invention relates in general to data processing systems, and in particular, to determining an age function within a microprocessor.
BACKGROUND INFORMATION
In the class of microprocessors where instructions are issued and executed out of order, commonly a structure is needed to determine if any dependent instructions are executed out of order thereby generating an erroneous result. This structure typically requires the relative age (as determined by the program counter) of the instructions in determining if an error occurred. Since instruction streams are very long, it is impracticable to implement a structure large enough to hold an entire stream of instructions, so a structure of limited size is used, wherein once the end of the structure is reached, the entries are wrapped around to the beginning. Additionally, the structure typically holds a variety of information on each instruction.
Assume a cyclical queue and the position of an entry in the queue determines its relative age, with entries closer to the tail pointer being older than entries closer to the head. To determine the oldest valid entry in the queue, start at the tail of the queue and check the validity of that entry. If that entry is valid, then it is the oldest entry in the queue. If that entry is not valid, then check the next entry in the queue. If that entry is valid, then it is the oldest entry in the queue; or if that entry is not valid, move to the next entry in the queue. This process is repeated until a valid entry is found or the head pointer is reached.
Searching for a valid entry in this fashion is the definition of an age function. However, such a serial process is timely and inefficient. Therefore, there is a need for a more efficient means for determining the age function in a processor.
SUMMARY OF THE INVENTION
The present invention addresses the foregoing need by providing a system and method within a processor for determining an age function by performing a logical function on each entry residing within a queue, determining when a particular one of the entries residing in the queue was stored in the queue relative to the other entries, and determining an oldest or youngest entry residing in the queue relative to the logical functions performed on each of the instructions. In one embodiment of the present invention, the entries are instructions temporarily stored within a queue in the processor. The logical function performed may determine which of the instructions is valid. The queue may be cyclical.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.
REFERENCES:
patent: 5774712 (1998-06-01), Cheong et al.
patent: 5805849 (1998-09-01), Jordan et al.
patent: 5897666 (1999-04-01), Mallick et al.
patent: 5931957 (1999-08-01), Konigsburg et al.
Frederick, Jr. Marlin Wayne
Ronchetti Bruce Joseph
Tran Cang
An Meng-Ai T.
England Anthony V. S.
International Business Machines - Corporation
Kordzik Kelly K.
Monestime Mackly
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