WO2000077613A2

WO2000077613A2 - Method and system for managing and using persistent storage

Info

Publication number: WO2000077613A2
Application number: PCT/CA2000/000707
Authority: WO
Inventors: Bertrand Michaud; Stephen Maryka; Don Grant
Original assignee: Wind River International Inc.
Priority date: 1999-06-14
Filing date: 2000-06-14
Publication date: 2000-12-21
Also published as: WO2000077613A3; AU5381900A

Abstract

A method and system for managing persistent memory within an information appliance provides an implementation where that persistent memory is transparent to an application programmer. A store object is provided which has defined methods for reading from and writing to the persistent memory. The store object also has defined data type representations which allow a set of data representations to be employed in the persistent memory which make efficient use of the memory and these representations are transparently converted by the store object to and from those used in the appliance. By changing the read and write methods of the store and the data representations employed, the system and method can be used with a variety of persistent storage systems without requiring any changes to application programs.

Description

Method and System for Managing and Using Persistent Storage

FIELD OF THE INVENTION The present invention relates to a method and system for managing and using persistent storage. More specifically, the present invention relates to a method and system for managing and using persistent storage in an information appliance device, in a manner which is largely transparent to both users and developers of applications.

BACKGROUND OF THE INVENTION

Information appliances, or devices, are becoming more prevalent and widely used. Examples of information appliances include thin-client desktop computers, personal digital assistants (PDA's), wireless pagers and email devices, intelligent cell phones, etc. Typically, such devices have somewhat limited resources, both in terms of processor capabilities and available memory. Thus, designers of applications for such information appliances are forced to carefully design their applications to make the best use of the available resources.

In addition to concerns about the available amount of memory, information appliances also typically require memory which is persisted when the appliance is inactive. For example, many appliances require that user options or preferences, or other configuration information, be stored in a persistent memory. For general purpose information appliances, such as those which execute Java applications, the application itself can be maintained in persistent memory after it is loaded into the appliance. Persistent memory can be implemented with a variety of hardware including, flash ROM, EEPROM, battery backed-up static ROM, etc.

However, problems do exist with such persistent memory in that it is relatively expensive, and therefore must be used efficiently, and that, generally, access to persistent memory can be quite slow, both for reading and, particularly, writing. The relatively long time which can be required to write information to persistent memory can result in undesired "freezing" of an application when information is being written to the persistent memory by an application. Such freezing of an application can result in confusion for the user of the application, as the user may be led to believe that the appliance has crashed or that the application has experienced a logic error. Even when no confusion occurs, such freezing is generally undesirable as it interferes with the efficient interaction between the user and the device. Further, if a device is powered down, intentionally or unintentionally, while information is being written to persistent memory, the contents of the persistent memory can be in an unknown state when the device is next turned on. This can result in the device freezing or otherwise demonstrating undesired behavior and generally requires a hardware reset of the device to reset the persistent memory, losing all the contents in memory. After such a reset, any desired applications must be reloaded and/or data reentered into the device.

A further problem exists in that each type of persistent memory generally requires different techniques for writing and/or reading information. This necessitates that the developer of an application for an appliance create the application to correctly access information to the particular persistent memory in the appliance. Thus, the developer may be forced to create different versions of the application depending upon the particular type of persistent memory that is employed by the appliance the application is to be executed on. It is therefore desired to have a method and system for managing the use of persistent storage which is convenient for the developer of an application to use and which inhibits freezing or other undesired user interface delays.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel method and system for managing the use of persistent memory in information appliance which obviates or mitigates at least one disadvantage of the prior art.

According to a first aspect of the present invention, there is provided a method of managing the use of persistent memory in an information appliance, comprising the steps of:

(i) assigning a store obj ect to a contiguous block of writeable persistent memory in said appliance, said store object including at least one method to write information to said persistent memory, at least one method to read information from said persistent memory and a set of data type definitions which define first representations of data types for use between said store object and said appliance and second representations of the same data types for storing information in said persistent memory;

(ii) creating in RAM memory at least one section object associated with said at least one store object and associating each said at least one section object with an application or object loaded on said appliance, each said at least one section object interacting with said application or object to receive information from said application or object for storage and to provide stored information to said application or object; and

(iii) operating said store object to:

(a) retrieve information from said persistent memory in said second representations and to convert said retrieved data to said first representations, said converted information being stored in said at least one associated section object; and

(b) receive information from each said associated section to store a copy of said received information in said second representation in said persistent memory. According to another aspect of the present invention, there is provided an information appliance including persistent and non-persistent memory, comprising: a processor; a user input device; a user output device; non-persistent memory; writeable persistent memory; at least one store object associated with a contiguous block of said writeable persistent memory and having a first defined set of date type representations for information to be stored in said writeable persistent memory; at least one section associated with said at least one store object and being implemented in said non-persistent memory, each said section having a defined second set of data type representations for use by applications or objects loaded onto said appliance, said at least one store including at least one method to convert information in said at least one associated section to said first defined set of data type representations and to write said converted information to said writeable persistent memory and including at least one method to read information in said writeable persistent memory in said first defined data type representations and to convert said information to said second set of data type representations and to store said converted information in said at least one associated section objects. The present invention provides a method and system for managing persistent memory within an information appliance, where the implementation of that persistent memory is transparent to an application programmer. One more store objects are provided which have defined methods for reading from and writing to the persistent memory. Each store object also has defined data type representations which allow data representations to be employed in the persistent memory that make efficient use of the memory and these representations are transparently converted by the store object to and from those used in the appliance. These data type representations can be size-adjusted representations (i.e. - representing an integer in four bits for an application that can only have integer values between zero and fifteen) or can be the results of data compression operations (i.e. - compressing a multi-byte data structure or record with LZW compression, etc.) By changing the read and write methods of the store and/or the data representations employed, the system and method can be used with a variety of persistent storage systems without requiring any changes to application programs.

The present invention thus provides an interface between an application interacting with a memory on a device and the implementation of that memory, such that an application can be created independently of the memory implementation. Data type representations can be selected for storage efficiency, depending upon the implementation of the persistent memory, without impacting the design of the application as conversion between data type representations is performed automatically by the interface and thus is invisible to an application. BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:

Figure 1 shows a representation of an information appliance; and Figure 2 shows a schematic representation of a store object in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVITATION

In Figure 1, an information appliance is indicated generally at 18. Appliance 18 includes a processor 20, a user input device 24, a user output device 28, a communications interface 32, an array of non-persistent memory 36 (such as RAM memory) and an array of writeable persistent memory 40. Processor 20 can be any suitable processor as will occur to those of skill in the art, such as the micro Java-701 processor sold by Sun Microsystems or the MC68328 DragonBall processor sold by Motorola. User input device 24 can be a keyboard, touch screen, voice input mechanism or any other suitable input mechanism as will occur to those of skill in the art. User output device 28 can be a display panel, such as an LCD display, an audio device or any other suitable output device as will occur to those of skill in the art. Communications interface 32 can be an RS 232 port, an ethernet port, an infrared port or any other interface suitable for downloading information and applications into appliance 18 or uploading such information or applications from appliance 18, as will occur to those of skill in the art. Non-persistent memory 36 can be integral with processor 20 or can be separately provided or can be a combination of both, as desired. Writeable persistent memory 40 can be any suitable type of persistent memory including, battery backed up static RAM, EEPROM, Flash NAND, Flash NOR, etc.

Figure 2 shows an embodiment of the method and system of managing persistent storage in accordance with the present invention. In this embodiment, persistent memory 40 in appliance 18 is managed by a persistent memory manager 76 which keeps track of usage of persistent memory 40 to determine contiguous blocks of memory which are in use and/or which are free to be used. Each contiguous block of writeable persistent memory 40 has a store object 100 defined for it. Each store object 100 accepts configuration parameters which define the type of writeable persistent memory 40 that store object 100 is employing and has appropriate methods for writing to and reading this type of persistent memory 40.

Store object 100 also accepts configuration parameters to define how various atomic or composite data types, such as integers, BOOL's, strings, records, etc. are represented within persistent memory 40. For example, applications run on appliance 18 might require only unsigned integer values between zero and fifteen to be stored and store object 100 can be configured to represent these integers in four bits of memory within persistent memory 40. Similarly, a BOOL can be represented as a complete byte or as a single bit in persistent memory 40, etc. In some circumstances, such as for executable applications, objects or data records, the representation employed within persistent memory 40 can be the result of an explicit data compression operation, such as a LZW compression algorithm, which is applied to the data in the standard representation to obtain a compressed representation.

Each application or object 80 loaded onto device 18 requests needed persistent memory from persistent memory manager 76. Persistent memory manager 76 determines a store obj ect 100 with available memory and assigns that memory to the requesting application or obj ect 80 which then creates one or more section objects 104 for the assigned memory. Application or object 80 instantiates section objects 104 with an appropriate memory layout overlay to accommodate its memory needs. As shown in Figure 2, each section 104 can have a different overlay, as needed by application or object 80, which defines how the memory in section 104 is employed by the application or object 80 (i.e. - the six bytes can be two-byte unsigned integer values, the next byte is a Boolean, etc.) The application or object 80 to which a section object 104 is assigned can read from or write to that Section object 104 as required. As each store 100 can employ a different data type representation for use in writeable persistent memory 40, an application or obj ect can have sections 104 in different stores assigned to it. For example, an application or object 80 can employ an integer value that is always between zero and fifteen in value, and can thus be represented by four bits, and another integer value that can vary between zero and two hundred and fifty five, and thus requires eight bits for representation. In such a case, the first integer value can be assigned to a section 104 in a store 100 that employs a four bit representation for integers in writeable persistent memory 40 and the second integer value can be assigned to a section 104 in a store 100 that employs an eight bit representation for integers in writeable persistent memory 40.

Applications or objects 80 communicate with section 104 to access stored data and section 104 employs standard data type representations defined for the appliance, such as the standard data types of JAVA. Thus, an application or object 80 reading character data from a section 104, will always read an eight bit character value, even though such data could be represented within writeable persistent memory 40 as a four bit value. Similarly, an application or object 80 can write data to section 104 in standard data type representations.

When a write method is invoked by store object 100 to store data in one of its sections 104 in persistent memory 40, the method of the store object 100 first converts the data from the standard data type representation used by applications and/or objects 80 loaded in appliance 18 to the data representation of that data type employed by the store object 100 for the persistent memory and then writes the new representation to persistent memory 40.

When a read method is invoked by Store object 100 to retrieve data from persistent memory 40 to a section 104, the read is performed and the method then converts the read data from the persistent memory representation of that data type to the corresponding representation used for that data type in appliance 18.

Store object 100 and section objects 104 provide a layer of abstraction between an application or object and persistent memory 40. In particular, the actual type of memory with which persistent memory 40 is implemented is hidden from an application or object. Instead, each application or object merely accesses its appropriate Section objects 104 to achieve its persistent storage needs. Each section object 104 acts to cache the current contents of its corresponding block of persistent memory 40 by having its corresponding store object 100 read the contents of that block and convert the data type representations if needed. The retrieved and converted data is then stored in non- persistent memory 36 (e.g. RAM memory), within section object 104, for access by applications or objects 80 with appliance 18.

It is contemplated that, as part of the initialization operations that occur upon activation of appliance 18, or upon an application being first executed or an object being instantiated, each section 104 will have its corresponding store object 100 read the contents of tis corresponding block in persistent memory 40. The contents of section 104 can then be read, as desired, by the application or object to which Section object 104 is assigned and that application or object need not concern itself with the details of the data type representation actually employed in persistent memory 40 and/or any special requirements (additional wait states, etc.) that are required to read from persistent memory 40.

Similarly, an application or object 80 can write to a section 104 assigned to it and the data written will be maintained in section 104. In a present embodiment of the invention, information placed in a section 104 by an application or object 80 is not written to persistent memory 40 until a commit function is performed by store 100. Upon receipt of a commit function from a section 104, the write method of store 100 is invoked to convert the data type representation, if necessary, of the information to be stored in persistent memory 40 and to then write that information accordingly.

Presently, there are two supported commit functions, the first of which is a safe commit which employs transactional procedures to ensure that the contents of the block of persistent memory 40 corresponding to a store 100 are in a known state, i.e. - either the entire contents of the sections 104 in a store 100 are successfully written to the block of persistent memory 40 or the contents of that block are restored to their pre-write values. The second write function is a non- transactional commit where the contents of the sections 104 of a store 100 are written without transactional control procedures. In one embodiment of the present invention, the safe commit function operates to have persistent memory manager 76 set a flag and allocate another block of writeable persistent memory 40 to the store 100 to be written. The write operation, including any necessary data type conversions, is performed to the new block of memory in persistent memory 40. Upon successful completion of the write operation, the flag in persistent memory manager 76 is cleared and the block of memory previously allocated to the store object 100 is freed for reuse. If the write operation fails or is otherwise interrupted, the flag in persistent memory manager 76 is not cleared and persistent memory manager 76 restores the association of store 100 with its previous block of persistent memory 40, whose contents have not be effected by the failed write operation and is thus in a known state. Persistent memory manager 76 then returns a message to the application or object 80 which initiated the write operation that the write failed. The application or object 80 can then attempt to re-write the information, if desired.

The methods employed by store 100 for writing the contents of sections 104 to persistent memory 40 can be performed in a separate thread of processor 20 to avoid "freezing" of an application while the data is written to persistent memory 40. Further, as will be apparent to those of skill in the art, as applications and/or objects 80 communicate with sections 104, which are implemented in RAM memory, they can read data from and/or write data to sections 104 at the fastest speed capable by appliance 18, or at least at a speed which is not limited by the access speed of the persistent memory.

The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.

Claims

We claim:

1. A method of managing the use of persistent memory in an information appliance, comprising the steps of:

(i) assigning a store object to a contiguous block of writeable persistent memory in said appliance, said store object including at least one method to write information to said persistent memory, at least one method to read information from said persistent memory and a set of data type definitions which define first representations of data types for use between said store object and said appliance and second representations of the same data types for storing information in said persistent memory;

(iii) operating said store object to:

(b) receive information from each said associated section to store a copy of said received information in said second representation in said persistent memory.

2. The method of claim one wherein step (iϋ)(a) is performed as part of the initialization of said appliance.

3. The method of claim 1 wherein step (iii)(b) is only performed upon receipt by said store object of an explicit command.

4. The method of claim 1 comprising at least two store objects, each having at least one section object associated therewith, each of said at least two store objects employing a different second representation and the same first representation.

5. The method of claim 1 wherein said second representation is the output of a compression operation performed on information in said first representation.

6. The method of claim 1 wherein step (iii)(b) is performed with transactional processing control.

7. An information appliance including persistent and non-persistent memory, comprising: a processor; a user input device; a user output device; non-persistent memory; writeable persistent memory; at least one store object associated with a contiguous block of said writeable persistent memory and having a first defined set of data type representations for information to be stored in said writeable persistent memory; at lease one section associated with said at least one store obj ect and being implemented in said non-persistent memory, each said section having a defined second set of data type representations for use by applications or objects loaded onto said appliance, said at least one store including at least one method to convert information in said at least one associated section to said first defined set of data type representations and to write said converted information to said writeable persistent memory and including at least one method to read information in said writeable persistent memory in said first defined data type representations and to convert said information to said second set of data type representations and to store said converted information in said at least one associated section objects.