Abstract:
In a Java Virtual Machine in which information is gathered about what sections of code get used most frequently in an embedded application. This information comprises binary data which is saved into non-volatile random access memory (RAM). The binary data is compressed for storage. At a subsequent startup, the stored compressed data is retrieved and decompressed and written to a volatile memory.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims benefit of the priority of U.S. Provisional Application No. 60/318,035, filed Sep. 7, 2001 and entitled “Embedded Java Virtual Machine.” 
     
    
     
       FIELD OF INVENTION  
         [0002]    The present invention relates to a data processing system and method, and more particularly to improving performance and execution of Java programs.  
         BACKGROUND OF THE INVENTION  
         [0003]    The present invention provides particular utility in embedded systems, although it is applicable to other systems as well. Embedded systems generally comprise processors placed in an environment for a particular use, for example, process control, as opposed to being provided in a desk top computer to be available for virtually any application which can be hosted on that computer. Generally, an embedded computer is utilized for a narrow range of applications. To use Java code, embedded systems will include a Java Virtual Machine (JVM). A JVM translates Java program code, referred to as byte code, into instructions for a device. The JVM may be implemented either as a software structure or it may be implemented in hardware as an ASIC or FPGA. Java itself is platform independent. The Java commands are translated into native code.  
           [0004]    Originally, the JVM was a command interpreter. Each line of Java code would have to be decoded and run independently. Consequently, Java programs would run more slowly than compiled C or C++ code. A more recent technique to speed Java processing is just-in-time (JIT) compiling. Frequently used small sections of Java code are compiled and saved in a random access memory (RAM). When the frequently used section is encountered, it is accessed from the RAM rather than being recompiled. A number of prior art arrangements exist for characterizing parts of code that are being run most frequently.  
           [0005]    In the general purpose personal computer (PC) environment, there is no motivation to store the permanent compiled sections permanently. There is usually a constant variety of applications being run. However, in an embedded environment, generally, a limited number of functions are being performed. For example, it may be desirable to run one routine such as on-screen display. Using the prior art, it would be necessary to characterize the most frequently run routines each time upon start-up. It is impractical to perform this function for general purpose computers due to the extremely wide range of applications that may be encountered.  
           [0006]    This problem has been approached by providing a Java Virtual Machine in which information is gathered about what sections of code get used most frequently in an embedded application. This information is saved into non-volatile random access memory (RAM). When a Java Virtual Machine is started, it loads its particular application, for example, on-screen display, and the characterization information from the non-volatile RAM. Native code is compiled, and full-speed operation is provided from the outset of operation.  
           [0007]    The kind of non-volatile memory used to store this data is very expensive. It is desirable to reduce the memory footprint required in embedded systems in particular. Embedded systems may, for example, be embodied in mass produced items such as appliances, where price is a critically important factor. It is also desirable to provide maximum capacity for a given amount of memory.  
         SUMMARY OF THE INVENTION  
         [0008]    In a Java Virtual Machine in which information is gathered about what sections of code get used most frequently in an embedded application. This information comprises binary data which is saved into non-volatile random access memory (RAM). The binary data is compressed for storage. At a subsequent startup, the stored compressed data is retrieved and decompressed and written to a volatile memory. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The invention may be further understood by reference to the following description taken in connection with the following drawings:  
         [0010]    Of the drawings:  
         [0011]    [0011]FIG. 1 is an illustration of a typical software stack for an embedded application;  
         [0012]    [0012]FIG. 2 is a block diagram of a Java processor operating in the context of FIG. 1.  
         [0013]    [0013]FIG. 3 is flow chart of the prior art technique for identifying frequently used code sections;  
         [0014]    [0014]FIG. 4 is an illustration of a program having typical user scenarios; and  
         [0015]    [0015]FIG. 5 is a flow diagram illustrating operation of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0016]    [0016]FIG. 1 illustrates a typical software stack for an embedded application and describes the hardware and software environment for the Java environment. The Java stack  100  includes an application layer  110  including applications and platforms. The application layer  110  interfaces with a Java technology layer  120 . The Java technology layer  120  includes a Java application program interface  124 . Applications developed for the embedded systems can use the Java application program interface and Java class libraries in the Java platform. The Java technology layer  120  interfaces with a real-time operating system  130 , which includes device drivers  134 . The real-time operating system layer  130 . As used in this description, the term operating system includes device drivers. The Java application program interface  124  operates within the hardware context of the embedded system. In the example in which a display is being driven, a central feature is a data pipeline. The application program interface  124  provides an abstraction that allows the application programmer to remain unaware of the details of the underlying display hardware environment.  
         [0017]    [0017]FIG. 2 is a block diagram of a client computer, or processor,  200  embodying a Java Virtual Machine  210 . Note that in this embodiment the Java Virtual Machine is a software structure and embodied with the memory of the client computer  200 . Within the computer  200 , computer hardware  220  is controlled by the operating system  230 . The Java Virtual Machine  210 &#39;s operations are implemented on the operating system  230  and computer hardware  220 . The Java Virtual Machine  210  executes a program  250  loaded into the computer system  200  or otherwise accessed thereby. Java programming normally comprises class files. A Java interpreter  260  interprets Java byte codes one by one. A just-in-time (JIT) Java compiler  270  produces native code to be run on the computer hardware  220  and provides compiled code in a compiled code register  280 . The compiled code register  280  provides object code for operations called by the Java Virtual Machine  210  to the computer hardware  220 .  
         [0018]    The program  250  also comprises software to perform the method of FIG. 3 below and command supplying of code to a compressor/decompressor  240  indicative of instructions identified by the operation of the method explained with respect to FIG. 3 below. Code representative of the most used software sections is compressed and stored in a code memory  290 . The code memory  290  comprises non-volatile RAM. Preferably the code supplied to the code memory  290  is compiled code. This compiled code is supplied for decompression via the compressor/decompressor to the compiled code register  280  on machine startup. Since code memory  290  is expensive, compression will decrease memory requirements and reduce the price of many embodiments. It is desirable that the compression and decompression be lossless so that code is not corrupted. The means which may comprise particular elements of the compression and decompression processing are well-known in the art. Varied means of compression and decompression without loss of data are available for this purpose.  
         [0019]    Operation is described with respect to FIG. 3, which is a flow diagram. Operation begins at block  300 , at which time execution of the program  250  is initiated. Since the memory  280  is volatile, compiling must begin each time operation is initiated. Compiling is indicated at block  302 . At block  304 , the identity of a current code section is sensed. A code section is a particular line of code or Java class that is compiled. At block  306 , a code section count is incremented for each section of code identified at block  304 . At block  308 , frequently used sections of compiled code are identified. “Frequently” is defined by a pre-selected threshold count reached over a preselected time period.  
         [0020]    Once frequently used code sections are identified, code indicative thereof is accessed. The accessed code is preferably compiled. The code is compressed at the compressor/decompressor  240  and written to the code memory  290  at block  312 , may be invoked from the memory  280  (FIG. 2).  
         [0021]    [0021]FIG. 4 is an illustration of an abbreviated source code listing for an embedded program. For purposes of the present example, the embedded program is running an on-screen display. Routines  410  are functions performed by the program  400 . Different routines  410  can be selected based on knowledge of programming of the application which will be the most used functions of the program  400 . The particular ones of the routines  410  that are selected as the most typical functions invoked by users are called for purposes of the present description typical user scenarios  420 .  
         [0022]    [0022]FIG. 5 is a flow diagram illustrating further operation and structure of the present invention. At block  500 , the program  400  is initiated. At block  502 , the first typical user scenario  420  is invoked. At block  504 , code sections that are utilized are identified. At block  504 , code is compiled. At block  506 , code sections invoked are identified. Frequently used sections are saved at block  508 . At block  510 , a determination is made as to whether a user scenario  420  is complete. Such determination is made by comparing the actual list of methods called in the user-invoked scenario to the total list of methods therein. If the user scenario is complete, then operation returns to block  502  to invoke a next user scenario, at the same time, a routine counter  512  is incremented. At block  514 , a determination is made as whether all user-invoked scenarios have been invoked and when they have, the program is stopped at block  516 . The invention does not require that all scenarios have to be converted to native code.  
         [0023]    In operation of FIG. 5, in addition, at block  508  the compiled code is compressed saved to non-volatile memory  290  (FIG. 2). When the Java Virtual Machine  210  (FIG. 2) is started again, it loads its on-screen display application  400 , which will constitute the program  250  in FIG. 2, and will have available characterization information from the non-volatile RAM  290 . The frequently used sections which are invoked in response to typical user scenarios  420  (FIG. 4) are decompressed and loaded immediately in the compiled Java code register  280 . Consequently the computer system  200  operates at full speed from the outset. The computer system  200  of FIG. 2 also represents a delivered product in which characterization information is loaded into the non-volatile RAM  290  prior to operation. Consequently, a computer product is provided which will operate on the program  400  at full speed from beginning of its operation.  
         [0024]    The above disclosure will enable those skilled in the art to provide a method, machine-readable medium and apparatus constructed in accordance with the present invention even while making many departures from the specific teachings above.