Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
1998-09-03
2001-01-30
Nguyen, Hiep T. (Department: 2759)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C711S152000, C711S166000, C713S152000
Reexamination Certificate
active
06182199
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to information handling systems, and, more particularly, to a system and method for granting permission to modify a memory area.
BACKGROUND OF THE INVENTION
A microcontroller is usually contained on a single integrated circuit, and is often intended to operate as an embedded system. In addition to a processing unit (e.g., a CPU), a microcontroller typically contains a small amount of random access memory (RAM), programmable read only memory (PROM), timers, and I/O ports. RAM is often in very short supply in embedded microcontroller applications. Often, it is limited to amounts in the 32 to 256 byte range.
Microcontrollers are often used to perform complex tasks in an information handling system. For example, a microcontroller may be used as a service processor for environmental monitoring within the system, early power off warning, error log analysis, etc. Microcontrollers are also used for data acquisition and control of subsystems, motion devices, input devices, display devices, instrumentation devices, etc.
Many software programs, including those written as embedded microcontroller applications, require that some type of permission or authority be acquired, before a memory location is modified. Usually, some type of permission variable is used to indicate that another variable, such as a data variable, may be updated. For example, before updating a counter, the application program checks a permission indicator variable. If the permission indicator variable is set to a certain value, the counter may be modified. If, however, the permission indicator variable is set to another value, the counter may not be modified.
Permission indicator variables can use a great deal of RAM. RAM is consumed for every memory area (e.g., the counters described above), and for each permission variable associated with the memory areas. In a typical processor, this is usually not a problem. However, in a microcontroller, where RAM is typically in short supply, this can be an overwhelming problem. Conserving even a small amount of RAM can make a major difference in the functionality of an embedded microcontroller application.
Consequently, it would be desirable to have a system and method for conserving RAM in an embedded microcontroller application. It would be desirable to have a permission, or locking, system for memory areas (i.e. variables) that does not consume valuable RAM space.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a system, method, and computer readable medium for granting permission to modify a memory area, such as a data variable stored in memory, without using valuable memory space to store permission variables. Rather than using separate permission variables, a portion of a data variable is used to indicate whether or riot the data variable may be modified.
The least significant bit of a variable (i.e. memory area) is used as a permission indicator. When the least significant bit is set to one, it is permissible to modify the variable. When the least significant bit is set to zero, it is not permissible to modify the variable. In one embodiment of the present invention, a counter variable is both checked for permission to increment, and incremented (if permission is; granted) in one step.
One advantage of the present invention is that it increases the efficiency of embedded systems, where memory space is typically in short supply. Because valuable memory space is conserved, more data may be stored in memory, and thus more data functions may be implemented in the embedded system. Further, because permission to modify a data variable is contained within the data variable itself, a program which desires to modify the data variable does not need to reference a permission, or locking, variable and test for permission to modify the data variable.
REFERENCES:
patent: 5592641 (1997-01-01), Fandrich et al.
patent: 5721872 (1998-02-01), Kasuta
International Business Machines - Corporation
Leeuwen Leslie A. Van
Nguyen Hiep T.
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