Patent Publication Number: US-8984457-B2

Title: System and method for a hybrid clock domain crossing verification

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present invention claims priority under 35′ U.S.C. 119(e) from prior U.S. provisional application No. 61/786,661, filed on Mar. 15, 2013. 
    
    
     TECHNICAL FIELD 
     The invention generally relates to integrated circuit (IC) verification processes and particularly to clock domain crossing (CDC) verification processes of an IC. 
     BACKGROUND ART 
     Clock domain crossing (CDC) verification is useful in the verification process of integrated circuit (IC) design. CDC verification requires a combination of structural and functional analysis followed by a thorough review and debug of issues by the designer. A designer typically makes assumptions based on which constraints are provided to improve accuracy of the analysis and generate fewer violations in a next run. The functional analysis involves computation-intensive analysis which may lead to incomplete analysis (partial proof). A designer may need to decide on the validity of his design with partial results which may be error prone, making for a hard decision. CDC verification cannot be closed without functional verification. Assumptions may be made during CDC verification which are not validated at any point. 
       FIG. 1  is a flowchart  100  of a method of the prior art of formal CDC verification. In S 110  a design of an IC and design constraints of the IC are received. In S 120  structural verification is performed. In S 130  the result is checked. If the result is a fail, execution continues with S 140 . Explicit assumptions are made in S 140  to fix, assume or waive the design constraints and execution is reiterated to S 110 . The result of S 130  may also be to pass under assumptions, in which case implicit assumptions are made. The result of S 130  may also be to continue to functional verification, which is performed in S 150 . In S 160  the result of the functional verification is checked. If the result is a fail, execution continues at S 140 . If the result is a pass or partial proof, execution ends. CDC verification may be closed with implicit assumptions, explicit assumptions and incomplete analysis. 
     In light of the deficiencies in the prior art, it would be advantageous to provide a system and method able to discover real design problems and provide clear guidance on when to close the verification process. It would be further advantageous that this process have a reasonable run time. 
     SUMMARY DISCLOSURE 
     A programmable system and a method implemented in such a system perform hybrid clock domain crossing (CDC) verification of the design of at least a portion of an integrated circuit. A description of the circuit is received into the system and a static (structural and/or formal) CDC verification is performed by a processor of the system using the received description. Likewise, a set of assertions and monitors are generated by the system from the received circuit description and a simulation of the circuit based on the generated assertions and monitors is performed. Results of the static CDC verification, the generated assertions and monitors, and results of the simulation are stored in a memory accessible by the system. For comprehensive coverage, the steps of static CDC verification, generation of assertions and monitors, and simulation of the circuit may be repeated based on the stored results for at least one additional iteration, which may cease upon achieving coverage better than a specified threshold figure of merit for such coverage. Analyzing the results may yield a modified description of the circuit, which may then be verified by the repeating the preceding steps for the modified circuit. The system includes a processor and memory coupled to the processing unit, the memory containing program instructions that when executed by the processor configure the system to perform the method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flowchart of a method of the prior art of Formal CDC verification (prior art). 
         FIG. 2  is a flowchart of Hybrid CDC verification according to an embodiment. 
         FIG. 3  is a block diagram of a system implemented in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A method of hybrid clock domain crossing (CDC) verification includes receiving a design or an integrated circuit (IC) design constraints. Static CDC verification is performed, including structural and functional verification. The result is checked and explicit or implicit assumptions are made to signoff verification. Incomplete formal analysis results are discarded after review. Assertions and monitors are generated by this process to capture the assumptions and check partially covered properties by formal analysis. A dynamic simulation is run using a testbench, the generated assertions and the monitors. The static verification and dynamic verification processes may be repeated until a satisfactory coverage is obtained. A system, such as a computer aided design (CAD) system, is configured to perform CDC verification of the IC design. The system may generate assertions and monitors to then run a simulation and determine coverage. Results are then reiterated through the system back to the static CDC verification. 
     Reference is now made to  FIG. 2 , which is an exemplary and non-limiting flowchart  200  of Hybrid CDC verification according to an embodiment. In S 210  a design of an IC, or portion thereof, or design constraints relating to an IC, or portion thereof, are received. In S 220  a static CDC verification is performed and assertions and monitors may be generated (S 226 ). This includes S 222  which describes performing structural verification, and S 224  which describes performing functional verifications. The result of the static CDC verification is checked in S 230 . If the result is a fail, execution continues to S 240 , where explicit assumptions may be made to fix or waive the issues before reiterating to S 210 . A simulation is run in S 250  based on the generated assertions/monitors. In S 260  the results of the simulation are checked and simulation is iterated at S 250  as needed to improve the dynamic coverage. Additionally, the dynamic coverage for the given monitors and assertions are fed back to the static verification at S 220 . Using this additional dynamic coverage data, a comprehensive CDC verification coverage may be generated which combines the static verification coverage as well as the dynamic verification coverage. Alternatively, the process may end at S 260  automatically or by a designer&#39;s input. 
       FIG. 3  shows an exemplary and non-limiting system  300 , such as a CAD system, implemented according to an embodiment. The system  300  comprises a processing element  310 , for example, a central processing unit (CPU) that is coupled via a bus  305  to a memory  320 . The memory  320  further comprises a memory portion  325  that contains instructions that when executed by the processing element  310  performs the method described in more detail herein. The memory may be further used as a working scratch pad for the processing element  310 , a temporary storage, and others, as the case may be. The memory may comprise of volatile memory such as, but not limited to random access memory (RAM), or non-volatile memory (NVM), such as, but not limited to, flash memory. The processing element  310  may be coupled to a display unit  340 , e.g., a computer screen, an input device  350 , e.g., a mouse and/or a keyboard, and a data storage  330 . Data storage  330  may be used for the purpose of holding a copy of the method executed in accordance with the disclosed technique. Data storage  330  may further comprise storage portion  335  containing the aforementioned formal CDC verification results, as well as, but not limited to, the results of the aforementioned simulation and any assertions or monitors generated in the process. 
     The principles of the invention are implemented as hardware, firmware, software or any combination thereof, including but not limited to a CAD system and software products thereof. Moreover, the software is preferably implemented as an application program tangibly embodied on a program storage unit or computer readable medium. The application program may be uploaded to, and executed by, a machine comprising any suitable architecture. Preferably, the machine is implemented on a computer platform having hardware such as one or more central processing units (“CPUs”), a memory, and input/output interfaces. The computer platform may also include an operating system and microinstruction code. The various processes and functions described herein may be either part of the microinstruction code or part of the application program, or any combination thereof, which may be executed by a CPU, whether or not such computer or processor is explicitly shown. In addition, various other peripheral units may be connected to the computer platform such as an additional data storage unit and a printing unit and/or display unit.