Abstract:
A method for verifying a logic circuit in a prototyping system includes (a) configuring programmable logic circuits of the prototyping system to implement the logic circuit and to implement probe circuits for accessing internal nodes of the logic circuit; (b) preparing emulation vectors for use in a vector emulation of the logic circuit in the prototyping system; (c) setting one or more vector substitution points; (d) preparing one or more packet vectors at each vector substitution point for replacing emulation vectors in the vector emulation; (e) performing the vector emulation using the emulation vectors until one of the vector substitution points is reached; and (f) substituting packet vectors for the corresponding emulation vectors at vector substitution point and continuing the vector emulation.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to tools for designing an integrated circuit. In particular, the present invention relates to tools for verifying a logic circuit using an integrated prototyping system which implements the logic circuit in programmable logic circuits. 
         [0003]    2. Discussion of the Related Art 
         [0004]      FIG. 1  is a block diagram of conventional co-emulation system  100 , including a host workstation  101  and emulation hardware  102 . Co-emulation system  100  is suitable for use in verification of a logic circuit. As shown in  FIG. 1 , a portion  201   c  of a user&#39;s design may reside in software form (i.e., expressed in a hardware description language, such as “Verilog”) in workstation  101 , and the remainder  205  of the design are compiled into the programmable logic circuits (referred to as the “device under verification” or DUV  205 ) of emulation hardware  102  (e.g., an emulation platform built using field programmable gate arrays, or “FPGAs”). Emulation hardware  102  is often used for prototyping. 
         [0005]      FIG. 2  is a block diagram showing in greater details the elements of hardware and software environments in conventional co-emulation system  100 . As shown in  FIG. 2 , in a co-emulation process, workstation  101  includes simulation system  201 , which includes simulator  201   a , test bench  201   b  and portion  201   c  of the user&#39;s design which is expressed in the hardware description language. Simulator  201   a  simulates the operations described in test bench  201   b  and portion  201   c  of the user&#39;s design. The simulation in simulator  201   a  is driven in part by the input stimulus and control signals provided by test bench  201   b  and portion  201   c  of the user&#39;s design. Simulator  201   a  also interacts with DUV  205  in emulation hardware  102 . Typically, simulator  20  la generates stimuli and passes them to DUV  205  in emulation hardware  102  over a hardware interface (e.g., PCI bus  202 ) and receives responses from DUV  205  over the same hardware interface. As shown in  FIG. 2 , the hardware interface may include PCI interface circuits  202   a  and  202   b , provided on workstation  101  and emulation hardware  102 , respectively. 
         [0006]    In emulation hardware  102 , data acquisition controller  203  receives stimuli from simulator  201   a  via PCI interface circuits  202 . Acquisition controller  203  translates and routes the received stimuli to DUV  205  implemented on the programmable logic circuits  204 . The stimuli may be provided to DUV  205  as test vectors. 
         [0007]      FIG. 3  shows providing test vectors to a DUV in a circuit verification application from a test bench. As shown in  FIG. 3 , in an FPGA implementation, each test vector may be applied to one or more signals (e.g., “action” signals that encode control signals, data signals, and addresses which specify the routing of the data signals in the FPGAs). To verify the DUV, one or more sets of test vectors are applied to the DUV at specific time points (e.g., time points T 1 , T 2  and T 3 ). Beginning at each time point, a group of test vectors are applied over a number of clock cycles. The signals of the DUV responding to the stimuli from simulator  201   a  may be fed back to simulator  201   a  for evaluation, or to drive further simulation. In some applications, a large number of clock cycles must be executed before reaching a satisfactory verification coverage. 
         [0008]    Because simulator  201   a  does not have the inherent parallel execution advantage of emulation hardware  102 , the operations of simulation system  201  are limited by the substantially slower vector rate in simulator  201   a , relative to the vector rate that can be achieved in emulation hardware  102 . Thus, the ability to apply test vectors directly to the emulation hardware without intervention from simulator (often called “vector emulation”) would save a significant amount of time. Test vectors that are directly applied to the emulation hardware are referred as “emulation vectors.” 
       SUMMARY 
       [0009]    According to one embodiment of the present invention, a method for verifying a logic circuit in a prototyping system includes (a) configuring programmable logic circuits of the prototyping system to implement the logic circuit and to implement probe circuits for accessing internal nodes of the logic circuit; (b) preparing emulation vectors for use in a vector emulation of the logic circuit in the prototyping system; (c) setting one or more trigger conditions or time points as vector substitution points; (d) preparing one or more packet vectors for replacing a portion of emulation vectors at each vector substitution point in the vector emulation; (e) performing the vector emulation using the emulation vectors until one of the vector substitution point is reached; (f) substituting the packet vectors for the corresponding emulation vectors at the vector substitution point; and (g) continuing the vector emulation. The method may be extended to include resuming the vector emulation using emulation vectors until a next vector substitution point is reached; and substituting the packet vectors for the corresponding emulation vectors at that next vector substitution point; and continuing the vector emulation. Such steps of resuming vector emulation, substituting packet vectors at the vector substitution point, and continuing vector emulation may be repeated until all emulation vectors are exhausted. 
         [0010]    During a vector emulation, the clock signals in the logic circuit may be mapped to a reference clock signal which is used as a time base for all clock signals in the prototyping system. The packet vectors substituting emulation vectors may result in a different duration of vector emulation than the duration resulting from the emulation vectors being substituted. Probe circuits may be specified by a user through a workstation communicating with the prototyping system or may be automatically generated. 
         [0011]    According to one embodiment of the present invention, emulation vectors may be extracted from stimuli to the logic circuit and responses from the logic circuit in a co-emulation system. The prototyping system may be a part of that co-emulation system. The emulation vector may be extracted from stimuli to and responses from one or more emulations conducted in the prototyping system. Alternatively, the emulation vectors may be generated in a vector generator. The packet vectors may be received from a workstation communicating with the prototyping system. A user may specify the packet vectors through the workstation. Alternatively, a test bench module running on the workstation may provide the packet vectors. The packet vectors may be generated in a vector generator. The packet vectors may also be extracted from one or more emulations conducted using the prototyping system. 
         [0012]    The present invention is better understood upon consideration of the detailed description below, in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a block diagram of conventional co-emulation system  100 , including a host workstation  101  and emulation hardware  102 . 
           [0014]      FIG. 2  is a block diagram showing in greater details the elements of hardware and software environments in conventional co-emulation system  100 . 
           [0015]      FIG. 3  shows providing test vectors to a DUV from a test bench in a circuit verification application. 
           [0016]      FIG. 4  shows vector emulation examples  4 ( b ) and  4 ( c ) with vector substitution, in accordance with one embodiment of the present invention. 
           [0017]      FIG. 5  shows flow chart  500  illustrating a vector emulation with vector substitution, in accordance with one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    The present invention may be implemented in an integrated prototyping system such as the type of prototyping systems that are described in copending patent applications (“Copending Applications”): (a) U.S. non-provisional patent application, entitled “Method of Progressively Prototyping and Validating a Customer&#39;s Electronic System Design,” Ser. No. 11/953,366, filed on Dec. 10, 2007, and (b) U.S. non-provisional patent application, entitled “Integrated Prototyping System For Validating An Electronic System Design,” Ser. No. 12/110,233, filed on Apr. 25, 2008. The disclosures of the Copending Applications are hereby incorporated by reference in their entireties. In addition, the present invention takes advantage of the “vector emulation” technique disclosed in copending patent application (the “Vector Emulation Application”), entitled “Method and Apparatus for Debugging an Electronic System Design (ESD) Prototype,” Ser. No. 12/255,606, filed on Oct. 21, 2008. The disclosure of the Vector Emulation Application is also hereby incorporated by reference in its entirety. 
         [0019]    During an emulation, a snapshot is taken of the state variables of the DUV at a specified time point, and the input stimuli to the DUV and the output responses of the DUV for each clock period thereafter are captured and stored in a captured vector database. These captured values are available for subsequent retrieval as “emulation vectors.” The emulation vectors may be extracted using conventional co-emulation, or from stimuli and responses of the DUV implemented in the integrated prototyping system. The emulation vectors may also be generated using a vector generator. These emulation vectors are used in subsequent vector emulations. During each vector emulation session (e.g., during a debugging session), the waveforms of selected internal nodes of the DUV which are not specifically probed in the prototyping system may be constructed to provide visibility into internal nodes. Multiple vector emulation sessions may be used during a debugging process. The emulation vectors may be repeatedly used in multiple vector emulation sessions, so long as the circuit configurations in the prototyping system are not modified. 
         [0020]    In a debugging application, for example, a user of an integrated prototyping system (IPS), such as any of those disclosed in the Copending Applications, may specify a number of clock cycles (e.g., advance the emulation back to a time point of interest) for the duration of a vector emulation session, or may specify a trigger condition which satisfaction terminates the vector emulation. The emulation vectors are preferably specified relative to a system reference clock signal, rather than the numerous clock signals typically found in the DUV. During vector emulation, signal values at user-defined probe points and automatically generated probe points, and the state values of low-latency snapshots may be captured, which may be used to carry out bounded-cycle simulations. Bounded-cycle simulations are disclosed in the Vector Emulation Application. (In bounded-cycle simulation, sequential loops are eliminated and a simulation is carried out into loop-free resulting circuit for a specified sequential depth). 
         [0021]    As disclosed in the copending Vector Emulation Application, vector emulation may be carried out as “probe-based vector emulations,” “snapshot based vector emulations,” or various variations of such techniques (referred to as “hybrid vector emulations”). 
         [0022]    In each iteration of a probe-based vector emulation, the user specifies new points at which signal values are to be observed and new assertions to check. The integrated prototyping system then generates a set of required probe points, including selected ones of the user-specified probe points and the automatically generated probe points. The required user-specified probe points and the system-generated probe points are then configured into the prototyping system. Vector emulation is then carried out in the prototyping system using the reference clock for the required number of cycles, or until a vector substitution point is reached, using the previously captured emulation vectors. During the vector emulation, the signal values at the user-specified probe points and the system-generated probe points are recorded for each reference clock cycle. 
         [0023]    In each iteration of a snapshot-based vector emulation, the user specifies new probe or observation points for signal values to observe and new assertions to check. The integrated prototyping system then generates a set of required user-specified probe points and a set of required low-latency snapshots. The selected user-specified probe points and snapshot controls are then configured into the prototyping system. Vector emulation is then carried out in the prototyping system using the reference clock for the required number of cycles, or until a vector substitution point is reached, using the previously captured emulation vectors. During the emulation, the signal values at the probes are recorded for each reference clock cycle, together with the values of the state variables specified in the low-latency snapshots. 
         [0024]    As mentioned above, vector emulation may be carried out with a set of events each corresponding to a vector substitution point. The vector substitution point may be a specific time point or satisfaction of a trigger condition. The specific time point may be relative to the reference clock. The trigger condition may be expressed as a logic expression based on specified signals. A complex trigger condition may be specified as a sequence of trigger conditions. The complex trigger condition is triggered when all the component trigger conditions are satisfied. In some applications, the component trigger conditions may be required to be satisfied in a predetermined order. According to one embodiment of the present invention, when such a trigger condition is satisfied, one or more emulation vectors from that time point forward (e.g., for a specified number of reference clock cycles) may be substituted by an alternative set of test vectors, referred to as “packet vectors.” The vector substitution point may be specified by a user, extracted from a test bench or extracted from events identified in the DUV implemented on the integrated prototyping system. The packet vectors used in the substitution represent alternative test conditions. The responses of the DUV to the packet vectors are captured for analysis and as part of further verification of the DUV. In this manner, verification of the DUV may be carried out entirely in the integrated prototyping system without interaction by either the simulator or the test bench, resulting in great time-savings (e.g., several orders of magnitude in elapsed time required over conventional co-emulation). 
         [0025]      FIG. 4  shows emulation vector examples with vector substitution, in accordance with one embodiment of the present invention. Example  4 ( a ) represents a vector emulation in which the emulation vectors for each of time intervals (A s , A e ), (B s , B e ) and (C s , C e ) may be substituted by alternative packet vectors. Example  4 ( b ) represents substituting packet vectors for the emulation vectors of example  4 ( a ) over the same time intervals (A s , A e ), (B s , B e ) and (C s , C e ). Alternatively, as shown in example  4 ( c ), packet vectors may be provided that results in a different number of reference clock cycles than that the number of reference clock cycles resulting from the emulation vectors being substituted. 
         [0026]      FIG. 5  shows flow chart  500  illustrating a vector emulation with vector substitution, in accordance with one embodiment of the present invention. Emulation vectors are prepared in advance and may be updated in the course of performing vector emulation. At step  501 , the integrated prototyping system determines if the emulation vectors have been exhausted (i.e., the vector emulation is complete). If the emulation vectors have been exhausted, the vector emulation is terminated (step  502 ). Otherwise, at step  503 , the integrated prototyping system examines trigger conditions. If a triggering condition is satisfied, packet vectors are retrieved to replace the emulation vectors at step  504 . At step  505 , the integrated prototyping system emulates one vector on DUV then returns to step  501  for the next iteration. 
         [0027]    The detailed description above is provided to illustrate the specific embodiments of the present invention and is not intended to be limiting. Numerous variations and modifications within the scope of the present invention are possible. The present invention is set forth in the following claims.