Method of speeding up access to a memory page using a number...

Details Method of speeding up access to a memory page using a number... Method of speeding up access to a memory page using a number...

1999-11-12

2001-09-04

Robertson, David L. (Department: 2187)

Electrical computers and digital processing systems: memory

Addressing combined with specific memory configuration or...

For multiple memory modules

C711S105000, C365S230010, C365S230030, C365S238500

Reexamination Certificate

active

06286075

ABSTRACT:

FIELD OF THE INVENTION
The present invention pertains generally to computing systems. More specifically, the present invention relates to a providing access to shared resources in a computing system such as multi-processor computer systems and the like. More particularly, apparatus and methods using a reduced number of page tag registers to track a state of physical pages in memory systems are described.
BACKGROUND OF THE INVENTION
In the basic computer system, a central processing unit, or CPU, operates in accordance with a pre-determined program or set of instructions stored within an associated memory. In addition to the stored instruction set or program under which the processor operates, memory space either within the processor memory or in an associated additional memory, is provided to facilitate the central processor's manipulation of information during processing. The additional memory provides for the storage of information created by the processor as swell as the storage of information on a temporary, or “scratchpad”, basis which the processor uses in order to carry out the program. In addition, the associated memory provides locations in which the output information of the processor operating set of instructions are placed in order to be available for the system's output device(s).
In systems in which many components (processors, hard drive, etc) must share a common bus in order to access memory presents there is a high probability of memory access conflicts. Especially in the case of multiprocessor computer systems, and the like, in which systems utilizing different processors are simultaneously in operation, access to memory or other shared resources, becomes complex. Since it is likely that each of the processors or processor systems may require access to the same memory simultaneously, a conflict between processors will generally be unavoidable. Essentially, the operation of two or more processors or processor systems periodically results in overlap of the memory commands with respect to a common memory, or other shared resource, in the multi-processor computer system.
Conventional approaches to solving the problem of conflicting memory access requests to a shared memory include, in one case, complete redundancy of the memories used for each of the processors, and isolation of the processor systems. However, this approach to solving the problem of conflicting memory access requests often defeats the intended advantage of the multiple processor system. Such multiple processor systems are most efficient if operated in such a manner as to provide parallel computing operations upon the same data in which one processor supports the operation of the other. Conventionally, such processor systems may be either time shared in which the processors compete for access to a shared resource, such as memory, or the processor systems may be dual ported in which each processor has its own memory bus, for example, where one is queued while the other is given access.
Various approaches have been used to avoid the above described conflict problems. In one approach, the avoidance of conflicts is accomplished by sequentially operating the processors or by time sharing the processors. In this way, the processors simply “take turns” accessing the shared resource in order to avoid conflict. Such systems commonly used include “passing the ring” or “token systems” in which the potentially conflicting processors are simply polled by the system in accordance with a pre-determined sequences similar to passing a ring about a group of users.
Unfortunately, use of sequential processor access methodologies imposes a significant limitation upon the operation of the overall computer system. This limitation arises from the fact that a substantial time is used by the system in polling the competing processors. In addition, in the case where a single processor is operating and requires access to the shared memory, for example, a delay between the processor accesses to the shared resource is created following each memory cycle as the system steps through the sequence.
Another conventional approach to conflict avoidance relies upon establishing priorities amongst the processors in the computer system. One such arrangement provides for every processor having assigned to it a priority with the hierarchy of system importance. The memory controller simply provides access to the highest priority processor every time a conflict occur. For example, in a two processor system, a first and a second processor access a shared memory which is typically a dynamic RAM (DRAM) type memory device which requires periodic refreshing of the memory maintain stored data. Generally, the DRAM type memory is refreshed by a separate independent refresh system. In such a multi-processor system, both the processors and the refresh system compete for access to the common memory. A system memory controller will process memory access request conflicts, or commands, as determined by the various priorities assigned to the processors and the refresh system. While such systems resolve conflicts and are somewhat more efficient than pure sequential conflict avoidance systems, it still suffers from lack of flexibility.
Another approach to conflict resolution involves decision-making capabilities incorporated into the memory controller. Unfortunately, because the decision making portions of the memory controller are operated under the control and timing of a clock system, a problem arises in the substantial time is utilized in performing the actual decision making before the memory controller can grant access to the common memory.
Unfortunately, this problem of performing the actual decision making substantially erodes the capability of conventional memory controllers granting access to multi-bank type memory systems. In multi-bank type memory systems, the actual memory core is departmentalized into specific regions, or banks, in which data to be retrieved is stored. Although providing faster and more efficient memory access, the complexity required of conventional memory controllers in coping with a multi-bank memory device substantially slows the overall access time of the system as a whole.
In view of the foregoing, it should be apparent that apparatus and methods using a reduced number of page tag registers to track a state of physical pages in memory systems are are desired.
SUMMARY OF THE INVENTION
According to the present invention, a method of using a reduced number of page tag registers to track a state of physical pages in memory systems are is described. A memory bank in a multi-bank type memory having a quantity of N memory banks is accessed by a memory controller that includes a quantity of M page registers wherein the quantity of M page registers is less than the quantity of N memory banks such that not every one of the N memory banks is represented in the M page registers. A page register is arranged to store a selected bank number corresponding to a selected one of the M memory banks, an open page address located within the selected bank, and an open page status. The memory controller further includes an adjustable comparator unit coupled to each of the plurality of page registers and a random page register number generator arranged to randomly generate an integer between and including 1 and M. An incoming system address request is received that includes a requested bank number and a requested page number. a page register corresponding to the requested bank number is then located. The stored page address included in the located page register is then compared to the requested page address. The requested page in the memory bank corresponding to the requested bank number is then accessed when the stored page address matches the requested page address for the requested memory bank. The stored page using page address from the page register of the bank which number is given by random page register number generator is closed if the requested bank and stored page address do not match, whereas a new page using the page add

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