Electrical computers and digital data processing systems: input/ – Input/output data processing – Data transfer specifying
Reexamination Certificate
1998-12-11
2001-02-20
Shin, Christopher B. (Department: 2782)
Electrical computers and digital data processing systems: input/
Input/output data processing
Data transfer specifying
C710S107000
Reexamination Certificate
active
06192424
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to computer systems and more particularly to a bus arbiter for facilitating access to a storage medium in enhanced burst mode using freely specifiable address increments/decrements.
BACKGROUND OF THE INVENTION
In most, if not all, computer systems, one of the most frequently performed tasks is that of storage access. Whether it be for accessing instructions or data, or reading or writing information, computer systems need to access storage media such as memory, magnetic media, and optical media in order to operate. Because storage access operations are performed so frequently, any efficiencies that can be gained in the accessing process can significantly improve system performance. Conversely, any inefficiencies that are injected into the process can significantly degrade system performance.
Currently, a storage medium can be accessed using one of several known methodologies. The first and most general methodology involves the provision, by a host, of an address for each location in the storage medium that is to be accessed. In this context, the term host is used broadly to mean any entity that can access the storage medium, including an internal processor, an external processor or system, and any other entity. According to this methodology, each time a host wishes to access a location in the storage medium, the host sends an access request. Included in this access request is an address that specifically identifies the location to be accessed. Once received, the address is applied to the storage medium to access the appropriate location. To access another location, the entire process is repeated.
This methodology is effective for accessing any location in the storage medium. However, it is disadvantageous in that it incurs a significant amount of overhead. Specifically, note that for each and every access, the host needs to make a request. This overhead, referred to herein as “set up”, is relatively resource intensive and should be avoided if at all possible.
In certain situations, it is possible to minimize the set up that needs to be done to access a storage medium. One such situation is where multiple contiguous locations are to be accessed. For such a situation, a second known methodology, typically referred to as burst mode, can be applied. With burst mode, a host can access multiple contiguous locations with a single access request. The form of the request needs to be augmented, however. Specifically, the request needs to specify an address for the location at which access is to begin, and a length indicating the number of times the storage medium is to be accessed. Once the request is received by a burst mode enabled storage system, the address and the length are stored. Then, the stored address is applied to the storage medium to access the first desired location. To access the second location, the stored address is simply incremented by one address since the second location is contiguous to the first. Then, the incremented address is applied to the storage medium to access the second location. This process is repeated until the storage medium has been accessed the desired number of times. Note that in burst mode, set up is performed only once, at the beginning of the burst cycle. Unlike the general methodology, it is not performed for each and every location. Thus, burst mode significantly reduces the amount of overhead that is incurred in accessing a storage medium. The longer the length specified in the access request, the greater the savings in overhead.
While burst mode is advantageous, it is currently quite limited in its application. The current burst mode methodology cannot be used in many situations in which it would be advantageous to implement burst mode. One such situation is shown in
FIG. 1
, wherein information is stored in the form of an array having m rows and n columns. Such an array is typically stored in a storage medium in the form shown in
FIG. 2
, wherein the entire array is stored as a contiguous string of storage locations. In many applications, it is desirable to access only the information in a particular column of an array (e.g. col. 1). To achieve such an access for the array shown in
FIG. 1
, it would be necessary to access every nth storage location, as shown in FIG.
2
. Since these locations are not contiguous, however, the current burst mode methodology cannot be use. Instead, the general methodology, with its high associated overhead, would have to be employed. This is not a wholly satisfactory solution.
SUMMARY OF THE INVENTION
To overcome the shortcomings of the prior art, the present invention provides a mechanism for implementing an enhanced burst mode which allows burst mode to be carried out using a freely specifiable increment/decrement specified by the host. By making the increment/decrement freely specifiable, the present invention greatly increases the versatility of burst mode. This in turn makes it possible to use burst mode in many new and different applications.
According to the present invention, there is provided a bus arbiter for managing access to a storage medium. In one embodiment, the bus arbiter is coupled to the storage medium via an access bus having control, address, and data lines. The bus arbiter is also coupled to a plurality of hosts, all of which are coupled to a main bus. The primary function of the arbiter is to manage access by the hosts to the main bus, thereby managing access to the storage medium by the hosts.
The bus arbiter includes an arbitration mechanism, a request processing mechanism, and an enhanced burst mode control mechanism. These mechanisms are typically implemented in hardware using digital logic components. In one embodiment, the access manager further includes an address register, an incremental/decremental (I/D) register, and a count register. These components and registers cooperate to carry out the enhanced burst mode of the present invention.
In operation, the bus arbiter implements enhanced burst mode by first having the arbitration mechanism receive access requests from the plurality of hosts. In response, the arbitration mechanism determines which of the hosts is the next to gain control of the main bus. This determination can be made using any desired methodology, including a round robin, a first come first served, and a priority based approach. Once a host has been selected, the arbiter sends an acknowledgment signal to the selected host to inform the selected host that it can now access the main bus. In response to the acknowledgment signal, the selected host sends a set of request information onto the main bus.
For enhanced burst mode, the set of request information includes an address, an I/D value, and a count. The address specifies the location in the storage medium at which access is to begin, the I/D value indicates the amount by which to increment/decrement the address each time the storage medium is accessed, and the count indicates the number of times the storage medium is to be accessed. The I/D value can be freely set to any value desired by the host. Whether it is an incremental or decremental value is determined by the sign of the value. The set of request information typically also includes an indication of whether a write or a read operation is desired. The set of request information is received by the request processing mechanism, and in response, the request processing mechanism stores the address, the I/D value, and the count value into the address, I/D, and count registers, respectively.
Thereafter, the enhanced burst mode control mechanism takes over to control access to the storage medium. The main tasks of the control mechanism include: (1) generating the proper addresses for the locations in the storage medium to be accessed; (2) generating the appropriate control signals for accessing the storage medium; and (3) properly applying the addresses and control signals to the storage medium to access the proper locations. From the address included in the set of request information, the address of t
Oak Technology, Inc.
Shin Christopher B.
Truong Bobby K.
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