Abstract:
A computer software architecture for an embedded computer system. The architecture includes a hierarchy of software object classes. One classification contains object tables which capture device control law behavior expressed in statecharts. Another contains objects which collaborate to function as a logic engine for processing statechart information encoded into object tables. In order to promote reusability, the architecture is layered in increasing levels of system abstraction.

Description:
[0001]     This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 60/572,662, filed May 19, 2004, the contents of which are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to systems and methods for capturing device controller control laws in embedded computer systems.  
       BACKGROUND OF THE INVENTION  
       [0003]     Over the years, the responsibility for device control (e.g., pumps, valves, actuators and the like) has migrated to embedded processors. The traditional way of capturing the behavioral requirements for a device controller was with textural descriptions. While this approach worked for simple devices, it failed when confronted with more complex behaviors. Recognizing that device controller behavior is state oriented, coupled with the advent of powerful state machine modeling tools, capturing the behavior requirements in verifiable statecharts soon became the method of choice.  
         [0004]     While there are many ways to design embedded software that will carry out device control laws, they tend to be designed around the specific device functions, resistant to requirement changes, and do not take advantage of the statechart modeling environment. What is lacking is a sophisticated software architecture that embeds the actual statechart behavior, is designed for rapid change processing, and can be used with a family of devices.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention constitutes a radical departure from conventional embedded device controller design solutions pursued previously, such as those described above.  
         [0006]     According to one aspect of the invention, a computer software architecture is provided for capturing the properties and behavior of device control laws expressed in the form of state charts within a machine-implemented embedded device control application. The architecture includes a condition class for capturing one or more sets of conditions present in statechart models; an action class for capturing actions to be performed while in a particular state; a transition class for capturing sets of transitions between states; a group of state classes for capturing parallel state and sub-state interrelationships within a statechart; and a class for capturing time delays between state transitions.  
         [0007]     In accordance with another aspect of the invention, a computer software architecture is provided for processing control laws expressed in the form of state charts within a machine-implemented embedded device control application. The architecture includes an event recognition layer including at least one event recognizer object; a state determination layer including at least one state controller object; an event response layer including at least one event responder object; and a logic engine including a condition recognizer object, a logic parser object and a temporary storage object.  
         [0008]     To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a block diagram of a device and device controller with a layered object based software architecture in accordance with an exemplary embodiment of the present invention;  
         [0010]      FIG. 2  illustrates respective layers of the object based software architecture in accordance with the exemplary embodiment of the present invention;  
         [0011]      FIG. 3  illustrates the class structure used to capture statechart parametrics in accordance with the exemplary embodiment of the present invention;  
         [0012]      FIG. 4  is a state diagram illustrating exemplary statechart parametrics represented in the class structure shown in  FIG. 3  in accordance with the exemplary embodiment of the present invention;  
         [0013]      FIG. 5  is a block diagram representing the class framework for a logic engine that processes statechart parametrics in accordance with the exemplary embodiment of the present invention; and  
         [0014]      FIG. 6  is a state diagram representing control of a pump according to one particular example of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     The present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout.  
         [0016]     Although the invention is described herein with reference to a specific embodiment such as an embedded device controller, this is for purposes of illustration and clarity only, and should not be construed in a limiting sense. Those skilled in the art will readily appreciate that the invention can be generally utilized with any application wherein state oriented behavior is a parameter of primary interest. Furthermore, the invention is not limited to a particular style of statechart modeling, and can accommodate both Mealy and Moore styles within the same model.  
         [0017]     Referring initially to  FIG. 1 , a device control system  10  is shown in accordance with an exemplary embodiment of the present invention. The system  10  includes a device controller  12  which controls a device  14 . The device  14  may be any type of device without departing from the scope of the invention. For example, the device  14  may be a discrete device such a motor, pump, valve, actuator, etc. Alternatively, the device  14  may be a system or sub-system such as a brake control system, traction control system, monitoring system, etc.  
         [0018]     The device controller  12  may be any type of automated controller without departing from the scope of the invention. For example, the device controller  12  may be based upon any of a variety of micro-type controllers such as commercially available microcontrollers, microprocessors, etc. In addition, or in the alternative, the device controller  12  may be based upon larger controllers in the form of a dedicated personal computer, server, mainframe, etc. Still further, the device controller  12  may be based on configured hardware such as a programmable logic array (PLA), programmable logic controller (PLC), or the like.  
         [0019]     Furthermore, the device controller  12  is programmable in accordance with the layered object based software architecture of the present invention. As will be described in more detail below, the software architecture of the present invention is a layered architecture for processing control laws of the device  14  expressed in the form of state charts. The software architecture may be embodied in machine executable code which is executed by the device controller  12 . The machine executable code is stored in an information storage medium such as digital memory (volatile or non-volatile), magnetic disk, optical disk, floppy disk, etc., represented generally by  16 , which is accessed and executed by the device controller  12 . Alternatively, the software architecture may be embodied in the hardware design of the PLA, PLC, etc., again represented generally by  16 .  
         [0020]     In the exemplary embodiment of the present invention, the device controller  12  is an embedded device controller. In the context of the present invention, “embedded device controller” refers to a controller  12  which controls the device  14 , wherein the device  14  may or may not be part of a larger system.  
         [0021]     As is shown in  FIG. 1 , the device controller  12  issues control commands to the device  14  as represented by line  18 . In addition, the device controller  12  receives control signals from the device  14  as represented by line  20 . In a case where the device  14  is a motor, for example, the control commands may turn the motor on, off and vary the speed of the motor. The control signals, on the other hand, may indicate operation properties such as motor position, measured speed, current, etc. The software architecture of the present invention, as embodied in the device controller  12 , provides for control of the device  14  based on the state charts defining the operation of the device  14 .  
         [0022]     Referring now to  FIG. 2 , the embedded computer software architecture of the present invention is illustrated in its respective layers. Specifically, the software architecture of the present invention provides for performing the three main functions required within the domain of device controllers: event recognition, state determination, event response. The architecture includes an event recognition layer  22  of software objects having responsibility for detecting the occurrence of events that may trigger a change in the current state of the controller  12 .  
         [0023]     The event recognition layer  22  makes use of a logic engine  24  included within the software architecture. The logic engine  24  is composed of objects that can process logical expressions of parameters encoded in Reverse Polish Notation (RPN) or other tabular parsable format, for example. However, it will be appreciated that other forms of logical expressions are possible without departing from the scope of the invention. The software architecture further includes a state determination layer  26  having objects for condition evaluation, state determination and object coordination. The state determination layer  26  also makes use of the logic engine  24  objects. The software architecture additionally includes an event response layer  28 . The event response layer  28  contains objects responsible for issuing the device control commands associated with the control laws of the current state of the device controller  12 .  
         [0024]     As is discussed herein, a class framework is provided for encoding the conditions, structural components and interconnections found on statecharts, into a series of classes that are embedded within the device controller  12  and are operated on by the various software architecture layers  22 ,  26  and  28 . It will be appreciated that a “class” as referred to herein typically defines data, data types, and operations on the data. The realization of a specific case of a class or classes is an instance of the class or classes which is referred to herein as an “object”.  
         [0025]     The software architecture of the present invention provides a direct correlation between the device control requirements modeled in statechart format and the embedded device control software. One having ordinary skill in the art of object based programming will appreciate that the requirements may be modeled in a tool that uses standard statechart notation, and a utility can be written to extract the statechart elements from the tool and automatically populate the statechart class framework objects. The use of the architecture set forth herein in accordance with the present intention improves behavioral verification and end user understandability since the parameters within the embedded controller  12  directly correlate to elements within the requirements model. This software architecture also makes changes to the requirements easier to achieve by encoding the statechart elements into software structures rather than in-line code.  
         [0026]     The implementation of the logic engine  24  along with the event recognition layer  22  and state determination layer  26  provide strong support for reuse by being device independent thereby allowing the same architecture to support families of device controllers.  
         [0027]     With reference to  FIG. 3 , a simplified class diagram is provided to define the overall structure  30  and relationship of the embedded objects used to capture the various elements of a typical statechart. A generic statechart is provided for reference purposes in  FIG. 4 . Referring to  FIG. 3 , the structure  30  includes a condition class  32  provided to capture one or more sets of conditions. These conditions (including action expressions) are encoded in RPN and are used to determine whether or not a transition can be taken as well as for evaluating the assignment statement(s) for any “entry”, “during” or “exit” actions associated with a state. (See, e.g., State  1  in  FIG. 4 ). The structure  30  also includes an action class  34  provided to capture the actions to be performed while in a particular state. The expressions are encoded in RPN or other tabular parsable format and handled the same as conditions in the condition class  32 . For each state, the structure  30  identifies a link, such as an index, into the set of conditions for the entry, during and exit expressions associated with the state. A transition class  36  is included to capture the sets of transitions between states. Each transition (e.g., T 1  in  FIG. 4 ), is identified via a “From State” and a “To State” as well as with an index of a condition (e.g., C 1 :exp in  FIG. 4 ) used to evaluate if the transition should be taken.  
         [0028]     The set of transitions for a parallel state are grouped together. Since Harel&#39;s extensions to finite statemachine theory are embodied within most modern statechart modeling tools, the structure  30  of the present invention provides a group of state classes, e.g., a parallel and sub-states class  38 , for capturing both parallel state and sub-state interrelationships within a statechart. (See, e.g., State  2  in  FIG. 4 ). Because of the nature of real-time embedded controllers  12 , delays between transitions may need to be modeled. Accordingly, the structure  30  includes a class  40  to capture these requirements. (See, e.g., delay in  FIG. 4 ). The state chart model may also contain tables of logical expressions (conditions) captured within the condition class  32 , for example, whose resulting parameters appear within the body of the state chart.  
         [0029]     Referring now to  FIG. 5 , in the exemplary embodiment of the invention, the statechart objects described above in relation to  FIG. 3  are coupled with the objects of the event recognition layer  22  (consisting, for example, of a single event recognizer object), the state determination layer  26  (consisting, for example, of a single state controller object), and the event response layer  28  (consisting, for example, of a single event responder object), as well as to the logic engine objects  24 , to make a complete framework for processing the statechart control logic. A class diagram of the exemplary embodiment of the framework is shown in  FIG. 5 , with interface entity classes  44  and a command request queue class  46 , included as an example of how the framework would interface to the rest of an application architecture. The objects in each of these layers, as well as the coordination of their operations by the state controller object in the state determination layer  26  are discussed in greater detail below. Although the exemplary embodiment includes only a single object in the respective layers for sake of brevity, it will be appreciated that each layer may include any number of objects without departing from the scope of the invention.  
         [0030]     The individual functions of the state controller object within the state determination layer  26  include retrieving data from the entity classes  44  that is required to evaluate all of the conditions contained within the state chart structure  30 , determining the current state of operation based on the state charts, and using this information to generate a device(s) command(s) appropriate for the current state. The state controller class within the state determination layer  26  also coordinates the activities of a condition recognizer object  48 , the event recognizer object of the event recognition layer  22 , and the event responder object of the event response layer  28 .  
         [0031]     The condition recognizer object  48  is part of the logic engine  24 , and is responsible for evaluating sets of tabularized logical expressions used to set parameters which appear within the body of the state chart  30 .  
         [0032]     The event recognizer object within the event recognition layer  22  is responsible for evaluating the state transition criteria contained within the state chart  30 , and determining when a transition can be made to a new state based on the evaluated conditions. Once the current state is determined, the event recognizer in the event recognition layer  22  performs any associated entry, exit or during actions, which are stored in the action object  34  within the state chart structure  30 .  
         [0033]     The event responder object within the event response layer  28  assembles device commands from the state controller object in the state determination layer  26 , resolves any conflicts (conflicts can arise in complex applications in which a device may receive commands from multiple sources, in which case a priority scheme can be used) and queues the resulting command(s) for output to the device  14  via the command request queue  46 .  
         [0034]     Both the event recognizer object in the event recognition layer  22  and the condition recognizer object  48  use a logic parser such as an rpn calculator object  50  included in the logic engine  24  to evaluate their logical expressions. The rpn calculator object  50  is responsible for evaluating a tabular expression stored in Reverse Polish Notation, for example. It returns the result of the evaluation to the calling object. For added flexibility the rpn calculator object  50  in the exemplary embodiment of the invention supports boolean, integer and floating point parameters, which are common data types within embedded controller systems.  
         [0035]     A temporary storage object such as a stack object  52  also included in the logic engine  24  is utilized by the rpn calculator object  50  when performing its evaluations. The stack object  52  provides a last in first out (LIFO) storage mechanism for Boolean or numeric data. In the exemplary embodiment of the invention, the stack object  52  provides the classic stack operations of read, write and empty (e.g., push, pop and is empty).  
         [0036]     The layered object based state chart architecture described above not only meets the needs of the device controller domain, but is also capable of application as a generalized logic engine. Through the software architecture, a number of domain characteristics and advantages have been identified. For example, the system is tolerant to changes made to the statechart because they result in table object changes which therefore eliminates the need to re-verify the code within the various object layers. Since the objects within the various layers provide functions related to logic processing rather than operations functions, the system is highly reusable, thus providing improved long-term affordability and efficiency.  
         [0037]     Turning now to  FIG. 6 , an exemplary statechart diagram for controlling a pump device  14  between an on state and an off state is shown. In accordance with the software architecture of the present invention, the condition class  32  ( FIG. 3 ) may be populated as follows:  
         [0038]     CONDITION (Structures)  
                                                   static const CONDITION_T pv_transition_conditions[4] =           {            /* (index 1) L_OUTER_PUMP_COMMAND_PUMP_J1 -&gt;            PUMP_1_OFF */            BOOL_PTR, 1, NOT_CODE, END_CODE,            /* (index 2) L_OUTER_PUMP_COMMAND_PUMP_J1 -&gt;            PUMP_1_ON */            BOOL_PTR, 1, END_CODE,            /* (index 3) PUMP_1_ON -&gt; PUMP_1_OFF */            BOOL_PTR, 1, NOT_CODE, END_CODE,            /* (index 4) PUMP_1_OFF -&gt; PUMP_1_ON */            BOOL_PTR, 1, END_CODE           }                      
 
         [0039]     Similarly, the transition class  36  ( FIG. 3 ) may be populated as follows:  
         [0040]     TRANSITION (Structures)  
                                   static const TRANSITION_DEFINITION_T       pv_transition_definitions[5] =       {       { L_OUTER_PUMP_COMMAND_PUMP,          L_OUTER_PUMP_COMMAND_PUMP_J1,          JUNCTION, NO_ENTRY, NO_ENTRY },        { L_OUTER_PUMP_COMMAND_PUMP_J1,          PUMP_1_OFF, NO_JUNCTION, 1,          NO_ENTRY },        { L_OUTER_PUMP_COMMAND_PUMP_J1, PUMP_1_ON,       NO_JUNCTION, 2, NO_ENTRY },        { PUMP_1_ON, PUMP_1_OFF, NO_JUNCTION, 3,        NO_ENTRY },        { PUMP_1_OFF, PUMP_1_ON, NO_JUNCTION, 4,        NO_ENTRY }       }                  
 
         [0041]     The action class  34  ( FIG. 3 ) may be defined as follows:  
         [0042]     ACTION (Structures)  
                                             static const ACTION_DEFINITION_T pv_action_definitions[997] =       {         /* PUMP_1_ON entry (index 1) */         BOOL_CODE, ON, SET_BOOL_PTR, 2, END_CODE,         /* PUMP_1_OFF entry (index 2) */         BOOL_CODE, OFF, SET_BOOL_PTR, 2, END_CODE       }       static const INDEX_T pv_action_indices[4] =       {        /* entry, during, exit */            −1, −1, −1,   /* L_OUTER_PUMP_COMMAND_PUMP */       −1, −1, −1,   /* L_OUTER_PUMP_COMMAND_PUMP_J1 */       2, −1, −1,   /* PUMP_1_OFF */       1, −1, −1,   /* PUMP_1_ON */       }                  
 
         [0043]     The parallel and sub-states class  38  ( FIG. 3 ) may be populated as follows:  
         [0044]     PARALLEL &amp; SUB STATES (Structure)  
                                                   typedef enum pv_state_names_t           {           L_OUTER_PUMP_COMMAND_PUMP,           L_OUTER_PUMP_COMMAND_PUMP_J1,           PUMP_1_OFF,           PUMP_1_ON           }                      
 
         [0045]     For sake of efficiency, and thus avoid the need to copy data elements, a pointer table may be provided and each element of the state chart assigned a pointer ID. Although not necessary to the present invention, it will be appreciated that the pointer table may be included as part of the state chart structure  30 . In the exemplary application, the pointer table may be defined as follows:  
         [0046]     POINTER Table  
                                                   static BOOLEAN_T *const pv_common_boolean_ptrs[2] =           /* 1 */  &amp;A,           /* 2 */  &amp;PMP_State[Pump_1]                      
 
         [0047]     The RPN calculator  50  in the logic engine  24  may be configured as follows:  
         [0048]     RPN CALCULATOR  
                                   Description:       // Given a pointer to a tabularized condition in RPN and a table       of       // pointers to variables to be used to evaluate the condition,       the       // evaluate operation walks through the operands and operators       in       // the condition, performing the required operations, and       returns       // the result of the condition       /* Evaluate all codes for requested condition */        code_ptr = condition_ptr;        while ((code_ptr != 0) &amp;&amp; (*code_ptr != (CONDITION_T)       END_CODE))        {         switch (*code_ptr)         {          case BOOL_PTR:           /* Push referenced value onto boolean stack */           if (++code_ptr != 0)           {            if (variable_ptrs−&gt;boolean_ptrs[*code_ptr] !=       0)            {             temp_bool1 = *(variable_ptrs−               &gt;boolean_ptrs[*code_ptr]);             stack_push_boolean( temp_bool1 );            }           }           break;       .       .       .          case SET_BOOL_PTR:           /* Assign top of stack to referenced value */           if (++code_ptr != 0)           {            if (variable_ptrs−&gt;boolean_ptrs[*code_ptr] !=       0)            {             temp_bool1 = stack_pop_boolean();             *(variable_ptrs−&gt;boolean_ptrs[*code_ptr]) =             temp_bool1;            }           }            break;       .       .       .           case BOOL_CODE:            /* Push next value onto boolean stack */            if (++code_ptr != 0)            {             stack_push_boolean( (BOOLEAN_T) *code_ptr );            }            break;       .       .       .           case NOT_CODE:            /* Negate the top boolean stack value, push result       */            temp_bool1 = stack_pop_boolean();            if (FALSE == temp_bool1)            {             stack_push_boolean( TRUE );            }            else            {             stack_push_boolean( FALSE );            }            break;       .       .       .           case END_CODE:            break;           default:            /* Issue appropriate error */             appbite_report_status( UNKNOWN_OPCODE_FAULT,       FAIL, snapshot );            break;          }          code_ptr++;         }         if ( stack_is_empty ( BOOLEAN_STACK ) )         {          result = FALSE;         }         else         {          /* Return top of boolean stack as the final result */          result = stack_pop_boolean();         }         return result;       }  /* rpn_calculator_evaluate */                  
 
         [0049]     The device controller  12  as shown in  FIG. 1  may be programmed as set forth above in order to control a the pump  14 , as will be appreciated by those having ordinary skill in the art of programmable controls. Accordingly, additional detail is omitted herein for sake of brevity.  
         [0050]     As previously noted, the software architecture of the present invention provides a direct correlation between the device control requirements modeled in statechart format and the embedded device control software. One having ordinary skill in the art of object based programming will appreciate that the requirements may be modeled in a tool that uses standard statechart notation, and a utility can be written to extract the statechart elements from the tool and automatically populate the statechart class framework objects. The use of the architecture set forth herein improves behavioral verification and end user understandability since the parameters within the embedded controller  12  directly correlate to elements within the requirements model. This software architecture also makes changes to the requirements easier to achieve by encoding the statechart elements into software structures rather than in-line code.  
         [0051]     Although the invention has been shown and described with respect to certain preferred embodiments, it is obvious that equivalents and modifications will occur to others skilled in the art upon the reading and understanding of the specification. The present invention includes all such equivalents and modifications, and is limited only by the scope of the following claims.