Abstract:
The timing for a mixed circuit of a synchronous circuit and an asynchronous circuit classifies the synchronous circuit into a cyclic circuit and an acyclic circuit, and the asynchronous circuit into a cyclic circuit and an acyclic circuit. The cyclic circuit of the synchronous circuit and the cyclic circuit of the asynchronous circuit thus classified are subjected to a static timing analysis, whereas the acyclic circuit of the synchronous circuit and the acyclic circuit of the asynchronous circuit thus classified are subjected to a dynamic timing analysis. As a result, the timing analysis can be made considering a hazard of the synchronous circuit, and the circuit to be operated in response to a signal, as can be virtually deemed as a clock, is subjected to the static timing analysis so that the analyzing operation can be made efficient.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a designing analysis technique of an electric/electronic circuit (e.g., not only an electric circuit or a semiconductor integrated circuit but also an electronic circuit packaging the semiconductor integrated circuit) and, more particularly, to a static-dynamic timing analysis division sharing a static analysis and a dynamic analysis for a circuit to be subjected to the designing analysis (a circuit to be analyzed), a timing analysis method, and a storage medium stored with a program for causing a computer to execute the analysis method. 
     In the timing analysis of the electric/electronic circuit, a static timing analysis or both a dynamic timing analysis and a static timing analysis can be adopted in place of the dynamic timing analysis so as to improve the operating efficiency of the timing analysis. 
     The analysis flow adopting the aforementioned static timing analysis and dynamic timing analysis can be exemplified by a flow shown in FIG.  2 . In FIG.  2 : numeral  21  designates a circuit connection information to be analyzed; numeral  22  a timing designation and clock designation information of input/output signals; numeral  23  a conventional static timing analysis device; numeral  24  a signal information (pattern); numeral  25  a dynamic timing analysis device; and numeral  26  a circuit design phase. For the static timing analysis made in the static timing analysis device  23 , basically, the signal information of the individual circuit elements by a simulation is not required, but the timing and clock designations  22  of the input/output signals are performed to find out the slowest path (or critical path) between latches, and a setup timing analysis is made on whether or not the signal transmission on that critical path is better in time than the clock cycle. In the static timing analysis, moreover, the fastest path is found out among the latches, and a hold timing analysis is made on whether or not next data are to be fetched at the timing of the same clock. In the dynamic timing analysis made in the dynamic timing analysis device  25 , the signal information (or test pattern), as designated by  24 , of the individual circuit elements by the simulation is required, and the circuit connection of the analyzed circuit is activated for the simulation by inputting the signal information to the input terminals of the circuit connection information, as designated by  21 . 
     The timing analysis system for the electric/electronic circuit of the prior art is disclosed in Japanese Patent Laid-Open Nos. 198723/1998, 44590/1995 and 50499/1997, for example. 
     The technique, as disclosed in Japanese Patent Laid-Open No. 198723/1998, warrants the timing only by the static timing analysis for such one of the electric/electronic circuits as is provided in a mixed manner with a synchronous circuit synchronizing with a specific clock signal and an asynchronous circuit having no specific clock or failing to synchronize with the specific clock signal. 
     Japanese Patent Laid-Open No. 50449/1998 provides a technique for discriminating a synchronous circuit portion and an asynchronous circuit portion from a synchronous/asynchronous mixed circuit to make the static timing analysis for the discriminated synchronous circuit portion and the dynamic timing analysis for the discriminated asynchronous circuit portion. 
     In this technique of the publication, however, there is made neither a hazard (or spike noise) analysis for warranting the normal circuit operation at the synchronous circuit portion nor the application of the static timing analysis to the asynchronous circuit portion. 
     The circuit analysis system, as disclosed in Japanese Patent Laid-Open No. 44590/1995, decides whether or not a spike noise generating circuit is present in the circuit to be analyzed. However, the system is defective in that the analysis method is low in reliability. 
     SUMMARY OF THE INVENTION 
     In the timing analysis technique of the electric/electronic circuit, the static timing analysis of the prior art analyzes the timing of only a synchronous circuit of a designated clock. This makes it essential to designate the clocks individually. In the case of a hazard analysis for warranting the normal circuit operation at the synchronous circuit portion, moreover, the hazard analysis has to be made for the dynamic timing analysis by searching the portions individually. For the hazard analysis, it is insufficient to use the circuit analysis system, as disclosed in Japanese Patent Laid-Open No. 44590/1995. 
     Therefore, the timing analysis cannot be made unless it is possible to designate the clocks or to extract the circuit portion which may cause a hazard. 
     In this regard, we have clarified that when there is in an object circuit a clock generating circuit constructed of a circuit capable of being deemed as an arbitrary counter circuit, there arises a problem that it takes a long time to prepare the information for designating the clock and the instruction information for the setup analysis and hold analysis of the clock gate which has been frequently used in resent years for lowering the electric power. It has also been found that the analysis on whether or not the instruction information is correctly given for the aforementioned setup analysis and hold analysis cannot be made without analyzing the static timing analysis results to discriminate the pseudo errors manually thereby to take a number of steps for the analyses. 
     Moreover, the user has been required for inefficient works to select a circuit portion needing the hazard analysis of the synchronous circuit portion and to perform another operation for the circuit portion. It is less efficient to analyze the circuit portion requiring the hazard analysis manually. Even when the dynamic timing analysis method is used, there is required an inefficient work to teach the dynamic timing analysis device the circuit portion requiring the hazard analysis. It is thought that even the use of the circuit analysis system disclosed in Japanese Patent Laid-Open No. 44590/1995 is insufficient for pointing out the circuit portion requiring the hazard analysis. 
     An object of the invention is to provide a static-dynamic timing analysis method capable of making a highly reliable timing analysis efficiently and a storage medium stored with a program for causing a computer to execute the method. 
     Another object of the invention is to provide a static-dynamic timing analysis method capable of performing the extraction of the clock information of a synchronous/asynchronous mixed circuit efficiently and a storage medium stored with a program for causing a computer to execute the method. 
     Still another object of the invention is to provide a static-dynamic timing analysis method capable of performing the timing analysis considering the hazard occurrence probability in the synchronous/asynchronous mixed circuit efficiently and a storage medium stored with a program for causing a computer to execute the method. 
     A further object of the invention is to provide a static-dynamic timing analysis method capable of performing a highly reliable timing analysis considering the clock information and the hazard occurrence probability in the synchronous/asynchronous mixed circuit efficiently and a storage medium stored with a program for causing a computer to execute the method. 
    
    
     The foregoing and other objects and novel features of the invention will become apparent from the following description to be made with reference to the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing one example of a static-dynamic timing analysis system in its entirety according to the invention; 
     FIG. 2 is a flow chart showing the operations of one example of a static-dynamic timing analysis system, as has been examined by us, in its entirety; 
     FIG. 3 is a flow chart showing one example of the operations of the static-dynamic timing analysis system in its entirety according to the invention; 
     FIG. 4 is a flow chart showing one example of the operations of the static-dynamic timing analysis system, from a view point other than that of FIG. 3, according to the invention; 
     FIG. 5 is a flow chart showing one example of the internal operation of Step S 1  of FIG. 4; 
     FIG. 6 is a flow chart showing one example of the internal operation of Step S 1 _ 3  of FIG. 5; 
     FIG. 7 is a flow chart showing one example of the internal operation of Step S 1 _ 4  of FIG. 5; 
     FIG. 8 is a flow chart showing one example of the internal operation of step S 1 _ 4 _ 4  of FIG. 7; 
     FIG. 9 is a flow chart showing one example of the internal operation of Step S 1 _ 4 _ 4 _ 1  of FIG. 8; 
     FIG. 10 is a flow chart showing one example of the internal operation of Step S 3  of FIG. 4; 
     FIG. 11 is a flow chart showing one example of the internal operation of Step S 4  of FIG. 4; 
     FIG. 12 is a flow chart showing one example of the internal operation of Step S 2  of FIG. 4; 
     FIG. 13 is a flow chart showing one example of the internal operation of Step S 2 _ 2  of FIG. 12; 
     FIG. 14 is a flow chart showing one example of the internal operation of Step S 6  of FIG. 4; 
     FIG. 15 is a flow chart showing one example of the internal operation of Step S 6 _ 2  of FIG. 13; 
     FIG. 16 is a flow chart showing one example of the internal operation of Step S 7  of FIG. 4; 
     FIG. 17 is a flow chart showing one example of the internal operation of Step S 5  of FIG. 4; 
     FIG. 18 is a flow chart showing one example of the internal operation of Step S 8  of FIG. 4; 
     FIG. 19 is a flow chart showing another example of the internal operation of Step S 8  of FIG. 4; 
     FIG. 20 is a flow chart showing an example of the internal operation of Step S 9  of FIG. 4; 
     FIG. 21 is a flow chart showing an example of the internal operation of Step S 10  of FIG. 4; 
     FIG. 22 is a flow chart showing another example of the internal operation of Step S 10  of FIG. 4; 
     FIG. 23 is a flow chart showing an example of the internal operation of Step S 11  of FIG. 4; 
     FIG. 24 is a flow chart showing an example of the internal operation of Step S 11 _ 1  of FIG. 23; 
     FIG. 25 is a flow chart showing an example of the internal operation of Step S 11 _ 8  of FIG. 23; 
     FIG. 26 is a flow chart showing an example of the internal operation of Step S 11 _ 8  of Embodiment  2 ; 
     FIG. 27 is a circuit diagram of a counter candidate circuit as an example of an object circuit; 
     FIG. 28 is a circuit diagram of an attribute calculating circuit as an example of the object circuit; 
     FIG. 29 is a circuit diagram of a sorting circuit as an example of the object circuit; 
     FIG. 30 is a circuit diagram of a logic cone circuit as an example of the object circuit; 
     FIG. 31 is a circuit diagram of a clock selecting circuit as an example of the object circuit; 
     FIG. 32 is a circuit diagram of another clock selecting circuit as an example of the object circuit; 
     FIG. 33 is a circuit diagram of an asynchronous flip-flop/latch circuit as an example of the object circuit; 
     FIG. 34 is a timing chart showing the operations of the circuit diagram of FIG. 33; 
     FIG. 35 is a circuit diagram of an asynchronous transfer circuit as an example of the object circuit; 
     FIG. 36 is a circuit diagram of a multicycle-path circuit as an example of the object circuit; 
     FIG. 37 is an explanatory diagram showing a fundamental concept in its entirety on the divisions of a static timing analysis and a dynamic timing analysis for a synchronous/asynchronous mixed circuit by the static-dynamic timing analysis system according to the invention; 
     FIG. 38 is an explanatory diagram showing the steps of operations which can be replaced by those of Steps S 1 _ 4 _ 4 _ 4  and S 1 _ 4 _ 4 _ 5  of FIG. 8; 
     FIG. 39 is a flow chart showing still another example of the internal operation of Step S 8  of FIG. 4; and 
     FIG. 40 is a perspective view showing one example of a computer for reading and executing the static-dynamic timing analysis programs from a storage medium. 
    
    
     Representatives of the invention to be disclosed herein will be briefly described in the following. 
     Specifically, the timing analysis of the prior art for the synchronous/asynchronous mixed circuit is made, as shown in FIG. 37, such that the static timing analysis is assigned to the synchronous circuits ({circle around ( 1 )}, {circle around ( 2 )}) whereas the dynamic timing analysis is assigned to the asynchronous circuits ({circle around ( 3 )}, {circle around ( 4 )}). In the static-dynamic timing analysis circuit according to the invention, the cyclic/acyclic points of view are introduced into the synchronous/asynchronous circuits, as exemplified in FIG.  37 . Specifically, the synchronous/asynchronous mixed circuit is classified into the synchronous circuit and the asynchronous circuit from the view point of whether or not it is synchronized with a clock signal defined uniquely by the aforementioned external clock terminals, clock tree and so on. The aforementioned synchronous circuit is classified into the cyclic circuit ({circle around ( 1 )}) and the acyclic circuit ({circle around ( 2 )}), and the aforementioned asynchronous circuit is classified into the cyclic circuit ({circle around ( 3 )}) and the acyclic circuit ({circle around ( 4 )}). Moreover, the cyclic circuit ({circle around ( 1 )}) of the synchronous circuit and the cyclic circuit ({circle around ( 3 )}) of the asynchronous circuit are subjected to the static timing analysis, and the acyclic circuit ({circle around ( 2 )}) of the synchronous circuit and the acyclic circuit ({circle around ( 4 )}) of the asynchronous circuit are subjected to the dynamic timing analysis. In short, in the synchronous/asynchronous mixed circuit, all the synchronous circuits that are operated in synchronism with the clock signal specified uniquely by the external clock terminal, clock tree and so on are not subjected to the static timing analysis, but the circuit portion which may cause a hazard or the like is extracted and is subjected as the acyclic operation circuit portion (the acyclic circuit) in the synchronous circuit to the dynamic timing analysis. In the synchronous/asynchronous mixed circuit, on the other hand, all the asynchronous circuits that neither use nor are operated in synchronism with the clock signal specified uniquely by the external clock terminal, clock tree and so on are not subjected to the dynamic timing analysis, but the circuit portion which is fed with a signal, e.g., a stroke signal or a gated clock capable of being deemed as a virtual clock signal is extracted and is subjected as the cyclic operation circuit portion (the cyclic circuit) in the asynchronous circuit to the static timing analysis. From the view points thus far described, the static-dynamic timing analysis method according to the invention will be described in more detail. 
     [1] The static-dynamic timing analysis method has a static-dynamic timing analysis dividing operation by a static-dynamic timing analysis division unit ( 6 ) for determining the application of the static timing analysis or the dynamic timing analysis to an object circuit of the timing analysis. This static-dynamic timing analysis dividing operation includes a clock information recognizing operation to discriminate counter means (circuit means for generating a synchronous signal) in the object circuit and to discriminate the clock information in the object circuit (at S 6 ) on the basis of the information (at S 1 _ 3 ) of the discriminated counter means. This clock information recognizing operation is performed in a clock information recognition unit ( 11 ). By the aforementioned clock information recognizing operation, the information of the internally generated clock can be automatically recognized from the clock information to the external input pin fed with the clock signal, from the information of the external input pin fed with a set or reset signal, and from the information of the flip-flop or latch elements to be used for the synchronous/asynchronous set/reset or the synchronous/asynchronous load of the counter in the object circuit. As a result, it is easy to discriminate the synchronous circuit and the asynchronous circuit of the object circuit. 
     [2] In the item [1], the aforementioned clock information recognizing operation is based on the information discriminated thereby to discriminate (at S 3 ) from the object circuit the asynchronous transfer path between the synchronous circuit portion and the asynchronous circuit portion and the asynchronous transfer path between the synchronous circuit portions. In short, what is extracted is the circuit portion which requires no timing analysis. Since the aforementioned asynchronous transfer path is recognized, the data transfer path (i.e., the asynchronous transfer path requiring the timing analysis) through the flip-flops and latches fed with the acyclic signal in the object circuit as the clock, and the data transfer path (i.e., the asynchronous transfer path requiring no timing analysis) between the flip-flops and latches fed with the signals asynchronous from each other, i.e., the signals incapable of defining the phase difference between the foregoing signals when the power is ON can be recognized as the different asynchronous transfer paths. 
     [3] In the item [1], the aforementioned clock information recognizing operation is based on the information discriminated thereby to recognize (at S 4 ) the logic elements constructed the gated clock in the object circuit. When the signal having two or more clock attributes is inputted to the logic elements constructing the recognized gated clock (FIG. 31, FIG.  32 ), it is decided (at S 9 ) whether or not it is necessary to execute the setup analysis and the hold analysis of the gated clock, and it is decided (at S 10 ) what of the input signals having the aforementioned clock attributes the setup analysis and the hold analysis of the gated clock are to be executed with respect to. As a result, the instruction information for the setup/hold analyses of the gated clock by the static timing analysis can be prepared to execute all the setup/hold analyses of the gated clock by the static timing analysis. 
     [4] In the item [1], the aforementioned clock information recognizing operation is based on the information discriminated thereby to discriminate (at S 4 ) the logic elements constructing the gated clock in the object circuit and to discriminate (at S 9 ) whether or not the input signal with no clock attribute and to the logic elements constructing the discriminated gated clock belongs to a multi-cycle path, as exemplified in FIG.  36 . Since the multi-cycle path of the input signal with no clock attribute and to the logic elements constructing the gated clock is thus recognized, it is possible to execute the setup/hold analyses of the gated clock by the static timing analysis from which the pseudo error has been eliminated in advance. 
     [5] In the item [1], the aforementioned clock information recognizing operation is based on the aforementioned information discriminated thereby to discriminate (at S 2 ) the logic elements constructing the selection logic of the clock in the object circuit. In the recognizing of the data transfer path between the flip-flops and the latches, therefore, it is possible to analyze in advance the combination of the clocks to be fed to the flip-flops and the latches at the two ends of the aforementioned data transfer path. 
     [6] In the item [1], the aforementioned static-dynamic timing analysis dividing operation is further based on the information discriminated in the clock information recognizing portion thereby to decide whether or not a virtual clock can be defined with respect to the flip-flops and latches which are fed at their terminals with a signal other than the clock, and to set (at S 7 ) the virtual clock with respect to such flip-flops and latches fed at their clock terminals with the signal other than the clock as decided capable to define the virtual clock. Thus, the virtual clock is set by deciding whether or not the virtual clock can be defined with respect to the flip-flops and latches which are fed at their terminals with the signal other than the clock, so that the static timing analysis can also be applied to the asynchronous circuit. In other words, the asynchronous circuit is classified into the cyclic circuit and the acyclic circuit so that the static timing analysis can be applied to the cyclic circuit. As a result, it is possible to reduce the number of analyzing steps drastically. If the virtual clock is set to make the setup time and the hold time the most strict, moreover, the static timing analysis for the aforementioned asynchronous circuit can be made under the most strict condition. 
     [7] In the item [1], the aforementioned static-dynamic timing analysis dividing operation further includes an applying circuit portion recognizing operation to discriminate a static timing analysis applying circuit portion and a dynamic timing analysis applying circuit portion in the object circuit on the basis of the information discriminated by said clock information recognizing operation. This operation is performed at the applying circuit portion recognition unit ( 13 ). Since the static timing analysis applying circuit portion and the dynamic timing analysis applying circuit portion can be thus discriminated, it is possible to execute the recognition of the circuit portion requiring the hazard analysis at the synchronous circuit portion and the dynamic timing analysis to that circuit portion. 
     [8] In the item [7], the aforementioned applying circuit portion recognizing operation recognizes (at S 11 ) the dynamic timing analysis applying circuit portion so far as to cover the appearance of the flip-flop along the transmission path of the signals to the discriminated dynamic timing analysis applying circuit portion which is discriminated by the discrimination unit for discriminating the static timing analysis applying circuit portion and the dynamic timing analysis applying circuit portion. As a result, the dynamic timing analysis of the dynamic timing analysis applying circuit portion can be executed without considering the signal delay time in the data transfer path to the dynamic timing analysis applying circuit portion from the static timing analysis applying circuit portion. 
     [9] In the item [7], the aforementioned applying circuit portion recognizing operation discriminates (at S 11 ) the correspondence between the dynamic timing analysis applying circuit portion, which is discriminated by the recognition unit for discriminating the static timing analysis applying circuit portion and the dynamic timing analysis applying circuit portion, and the logic hierarchy in the object circuit. Since the correspondence between the dynamic timing analysis applying circuit portion and the logic hierarchy in the object circuit is thus discriminated, it is possible to recognize the logic hierarchy to execute the dynamic timing analysis. As a result, the input signal information to each logic hierarchy, as prepared at the logic analyzing time, can be diverted to execute the dynamic timing analysis thereby to expect the reduction in the number of analyzing steps. 
     [10] In the item [1], the aforementioned applying circuit portion recognizing operation: discriminates (at S 11 _ 8 _ 1 ) the flip-flops and latches outside of the aforementioned dynamic timing analysis applying circuit portion along the transmission path of the signal from the flip-flop, as the closest to the input terminals and the output terminals of the static timing analysis applying circuit portion discriminated thereby, in the dynamic timing analysis applying circuit portion; and adjusts (at S 11 _ 8 _ 2 ) the propagation delay of the clock signal to the flip-flop and latch discriminated by the aforementioned recognition unit, such that the dynamic timing analysis can be made merely by applying it as the propagation delay of the clock signal to the aforementioned dynamic timing analysis applying circuit portion and the flip-flops and latches in the aforementioned dynamic timing analysis applying circuit portion at the time of feeding the object circuit with only the delay information. As a result, by feeding the delay information to only the dynamic timing analysis applying circuit portion, it is possible to execute the dynamic timing analysis of the entire object circuit and to divert the input signal information of the entire object circuit, as prepared at the logic analyzing time. Thus, it is possible to expect the reductions in the time period for and the step number of the analyses. 
     [11] Especially, an analysis method noting the discrimination of the asynchronous transfer path comprises a static-dynamic timing analysis dividing operation to decide which of a static timing analysis or a dynamic timing analysis is to be applied to an object circuit for the timing analysis, and the aforementioned static-dynamic timing analysis dividing operation includes a clock information recognizing operation to discriminate a counter portion in the object circuit and to discriminate the clock information in the object circuit on the basis of the information of the discriminated counter portion. Moreover, the aforementioned clock information recognizing operation performs an asynchronous transfer path extracting operation (at S 5 ) to discriminate an asynchronous transfer path with a synchronous circuit portion and an asynchronous circuit portion in the object circuit and an asynchronous transfer path between synchronous circuit portions individually on the basis of the aforementioned discriminated information. Moreover, the aforementioned asynchronous transfer path extracting operation: admits the passage of an in-element path from a clock terminal to a data output terminal so as to recognize elements constructing an asynchronous transfer path; recognizes an operation to express a clock path passing from an external terminal through the element having admitted the aforementioned passage in a graph joining clock sources, an operation (at S 5 _ 1 ) to grasp a set of elements using the clock sources of the graph, and a data transfer between the elements using the clock sources of the aforementioned graph as clock sources and the elements not using the clock sources of the aforementioned graph as clock sources, as an asynchronous transfer for each of the aforementioned recognized graphs; recognizes the aforementioned path as the asynchronous transfer at all times if the elements of the path recognized as the asynchronous transfer use the apexes of the graphs different before and after the selection logic as the clock sources; and recognizes (at S 5 _ 2 ) the aforementioned path as the asynchronous transfer in accordance with the selected state of the selection logic if the elements of the path recognized as the asynchronous transfer use the apexes of the graphs identical before and after the selection logic as the clock sources. 
     As compared with the method for grasping the clock path by making divisions for every clock selection logics as in the multiplexer, the asynchronous transfer path extracting operation has less operation data by a computer so that the memory capacity necessary for the computer to operate and prepare the table can be reduced to complete the data processing quickly. 
     By storing and providing the program for causing the computer to execute the aforementioned static-dynamic timing analysis method in a computer-readable storage medium such as the floppy disk or the CD-ROM, the aforementioned static-dynamic timing analysis method can be easily practiced. 
     The storage medium is exemplified by storing a program for causing the computer to execute: a first operation to discriminate a counter unit in an object circuit to be subjected to a timing analysis; a second operation to discriminate clock information in the object circuit on the basis of the information of the discriminated counter portion; a third operation to discriminate a static timing analysis applying circuit portion and a dynamic timing analysis applying circuit portion in the object circuit on the basis of the discriminated clock information; a fourth operation to perform the static timing analysis on the basis of the result of the aforementioned third operation; and a fifth operation to perform the dynamic timing analysis on the basis of the result of the aforementioned third operation. 
     A storage medium according to another aspect of the invention is stored with the program for causing a computer to execute: an operation to extract such a synchronous circuit portion in a synchronous/asynchronous mixed circuit of the synchronous circuit and an asynchronous circuit as may cause an acyclic malfunction, and to make a dynamic timing analysis of the circuit portion as an acyclic circuit; and an operation to extract such an asynchronous circuit portion in the aforementioned synchronous/asynchronous mixed circuit as may be fed with a signal capable of being deemed as a virtual clock signal, and to make a static timing analysis of the aforementioned circuit portion as a cyclic circuit. 
     A storage medium according to still another aspect of the invention is recorded with a program for causing a computer to execute: classifying, for a synchronous/asynchronous mixed circuit for a clock signal, a synchronous circuit into a cyclic circuit and an acyclic circuit and an asynchronous circuit into a cyclic circuit and an acyclic circuit; making a static timing analysis for the cyclic circuit of the synchronous circuit and the cyclic circuit of the asynchronous circuit; and making a dynamic timing analysis for the acyclic circuit of the synchronous circuit and the acyclic circuit of the asynchronous circuit. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     &lt;&lt;Construction of Static-Dynamic Timing Analysis Device&gt;&gt; 
     FIG. 1 shows one example of a static-dynamic timing analysis device. In FIG. 1, reference numeral  5  designates a storage unit constructed of semiconductor storage elements and so on, and numeral  1  designates a connection information input unit for storing the storage unit  5  with the connection information of an object circuit, i.e., the information on the kinds of the elements constructing the object circuit and their connection states containing external input/output pins. Numeral  2  designates a delay information input unit for inputting the delay information of the individual elements, timing restriction information and so on and for storing them in the storage unit  5 . Numeral  3  designates a circuit restriction input unit for storing the storage unit  5  with the circuit restrictions for preventing any hazard from being caused, that is, the information on the restrictions on the kinds of elements constructing an input logic function to such terminals, e.g., the clock terminal and the asynchronous set/reset terminal of a flip-flop in the object circuit as may highly probably cause an erroneous action of the circuit when a hazard signal is inputted, and on their connection states containing the external input/output pins. Numeral  4  designates a load information input unit for inputting the resistance/capacity/inductance intrinsic to a circuit to be analyzed, and the resistance/capacity/inductance of the lines on the packaging substrate of the analyzed circuit and for storing them in the storage unit  5 . 
     A static-dynamic timing analysis division unit  6  recognizes a clock tree in the object circuit, a clock generating circuit constructed of a circuit, as can be deemed as an arbitrary counter, the waveform of an internally generated clock, elements constructing a clock gate, elements constructing a clock selecting logic and an asynchronous flip-flop/latch, and stores them in the storage unit  5 . On the other hand, the static-dynamic timing analysis division unit  6  analyzes whether or not the circuit construction satisfies the circuit restriction, as given in the circuit restriction input unit  3 , for preventing any hazard from being caused, and stores the analysis result in the storage unit  5 . Moreover, the static-dynamic timing analysis division unit  6 : defines a clock waveform for such one of the asynchronous flip-flops/latches discriminated as is decided to cause no hazard in the signal to the clock terminal and stores it in the storage unit  5 ; discriminates a dynamic timing analysis applying portion in the object circuit and stores it in the storage unit  5 ; recognizes the correspondence between the discriminated dynamic timing analysis applying portion and the logic hierarchy in the object circuit and stores it in the storage unit  5 ; and calculates the construction ratio between the static timing analysis applying portion and the dynamic timing analysis applying portion in each logic hierarchy and stores it in the storage unit  5 . 
     Numeral  7  designates a static timing analysis unit for performing the timing analysis of a circuit portion other than the dynamic timing analysis applying portion, as discriminated by static-dynamic timing analysis division unit, by a static timing analysis method. Numeral  8  designates a dynamic timing analysis unit for performing the timing analysis of the dynamic timing analysis applying portion, as discriminated by the static-dynamic timing analysis division unit  6 , by a dynamic timing analysis method. Numeral  9  designates a circuit simulation execution unit for executing a circuit simulation by adding the resistance/capacity/inductance intrinsic to the package, as given by the load information input unit  3 , and the resistance/capacity/inductance of the line on the board substrate to the clock tree accompanied by the arranging/wiring information after discriminated. 
     In the storage unit  5 , there are written the individual timing analysis results by both the static timing analysis unit  7  and the dynamic timing analysis unit  8 , and the circuit simulation execution result by the circuit simulation execution unit. As shown in FIG. 1, on the other hand, this device is provided with an output unit  10  for outputting the timing analysis result and the circuit simulation execution result to be stored in the storage unit  5 . 
     The static-dynamic timing analysis division unit  6  forming a main portion of this device is provided with a clock information extraction unit  11 , a circuit restriction analysis unit  12  and a circuit division unit  13 . Moreover, this circuit division unit  13  is provided with a dynamic timing analysis applying portion recognition unit  14  and a corresponding logic hierarchy recognition unit  15 . 
     The clock information extraction unit  11  outputs the object circuit information with the clock information and the asynchronous flip-flop/latch information to the circuit restriction analysis unit  8  and the storage unit  5  by propagating the information such as the waveform of the clock from the external clock pin of the object circuit and by recognizing the clock generating circuit constructed of an arbitrary counter in the object circuit, recognizing the elements constructing the clock gate and the elements constructing the selecting logic of the clock and recognizing the waveform of the clock internally generated by executing the simulation. 
     On the other hand, the output unit  10  outputs the object circuit information with the clock information and the asynchronous flip-flops/latches to be stored in the storage unit  5 . 
     The circuit restriction analysis unit  12  outputs the circuit restriction analysis result to the circuit division unit  13  and the storage unit  5  by analyzing whether or not the circuit construction satisfies the circuit restriction given by the circuit restriction input unit  3  for preventing the hazard from being caused, and outputs the asynchronous clock waveform information to the circuit division unit  13  and the storage unit  5  by defining the clock waveform with respect to such one of the discriminated asynchronous flip-flops/latches as has been decided to cause no hazard in the signal to the clock terminal. 
     On the other hand, the output unit  10  outputs the circuit restriction analysis result and the asynchronous clock waveform information to be stored in the storage unit  5 . 
     The dynamic timing analysis applying portion recognition unit  14  discriminates the static timing analysis applying portion and the dynamic timing analysis applying portion in the object circuit, and outputs the static timing analysis applying portion information, i.e, the information on the static timing analysis applying circuit portion to the storage unit  5  and the dynamic timing analysis applying portion information, i.e, the information on a dynamic timing analysis applying circuit portion to the corresponding logic hierarchy recognition unit  15  and the storage unit  5 . 
     The corresponding logic hierarchy recognition unit  15  outputs the corresponding logic hierarchy information to the storage unit  5  by recognizing the correspondence between the discriminated dynamic timing analysis applying portion and the logic hierarchy in the object circuit, and outputs the logic hierarchy construction ratio information to the storage unit  5  by calculating the construction ratio between the static timing analysis applying portion and the dynamic timing analysis applying portion in each logic hierarchy. On the other hand, the corresponding logic hierarchy information and the logic hierarchy construction ratio information to be stored in the storage unit  5  are outputted by the output unit  10 . This construction ratio is utilized for evaluating the re-usability as the design resources. 
     The static timing analysis unit  7  performs the timing analysis on the basis of the static timing analysis applying portion information outputted to the storage unit  5 , and outputs the result to the storage unit  5 . 
     The dynamic timing analysis unit  8  performs the timing analysis on the basis of the dynamic timing analysis applying portion information outputted to the storage unit  5 , and outputs the result to the storage unit  5 . 
     The circuit simulation execution unit  9  recognizes the object circuit information with the clock information, as accompanied by the arranging/wiring information, from the arranged/wired result on the basis of the object circuit information with the clock information, as outputted to the storage unit  5 , and executes the circuit simulation on the basis of the resistance/capacity/inductance intrinsic to the package, as stored in the storage unit  5 , and the resistance/capacity/inductance of the line on the board substrate and outputs the result to the storage unit  5 . 
     &lt;&lt;Processing Procedure of Static-Dynamic Timing Analysis Device Unit&gt;&gt; 
     FIG. 4 is a flow chart showing a processing procedure by the device of FIG.  1 . When the processing is started, as shown in FIG. 4, the clock information in the object circuit is recognized at first Step S 1 . 
     Next, on the basis of the clock information extracted at Step S 1 , the logic elements constructing the selecting logic of the clock, the flip-flops and the latches fed at their clock terminals with the acyclic signals, and the logic elements constructing the clock gate are recognized at Steps S 2 , S 3  and S 4 , respectively. Here, in the accompanying drawings, the letters “FF” indicate the flip-flop, and the letters “Latch” indicate the latch. 
     At Step S 5 , a data transfer path between the flip-flops and the latches fed with the mutually asynchronous clocks is recognized on the basis of the clock information and the logic elements constructing the selecting logic of the clock. 
     At Step S 6 , on the basis of the clock information and the information of the logic elements constructing the selecting logic of the clock, the connection information of the circuit of only the elements to generate the clock or to be propagated by the clock is generated to narrow the portion for generating the clock. After this, the clock waveform is recognized at the clock generating portion by simulating the connection information of the circuit which is newly constructed by the logic simulator. 
     The operations of the foregoing Steps S 1  to S 6  are executed at the clock information extraction unit  11 . 
     At Step S 7 , on the basis of the clock waveform information, a clock waveform candidate is defined with respect to the flip-flops and the latches which are fed at their clock terminals with the acyclic signals. 
     At Step S 8 , it is examined whether or not the circuit construction of the logic elements constructing the clock gate and the circuit construction of the logic elements to appear on the path to the enable terminal of a tristate buffer satisfy predetermined conditions. 
     At Step S 9 , on the basis of the clock waveform information and the information of the logic elements constructing the clock gate, it is decided whether or not the input signal path other than the clock to the logic elements constructing the clock gate may be a multi-cycle path. 
     The operations of the foregoing Steps S 7  to S 9  are executed in the circuit restriction analysis unit  12 . 
     At Step S 10 , on the basis of the clock waveform information, the information of the logic elements constructing the clock gate and the information of the aforementioned multi-cycle path, the gated clock analysis is executed by the static timing analysis device. This Step S 10  is executed at the static timing analysis unit  7 . 
     At Step S 12 , the analysis of the asynchronous reset is executed. 
     Finally at Step S 11 , the applying portion of the dynamic timing analysis is determined on the basis of a circuit construction violation, a timing violation portion in the gated clock analysis, and the information of the flip-flops and the latches fed at their clock terminals with an acyclic signal having failed to be defined by the clock. This Step S 11  is executed at the circuit division unit  13 . 
     FIG. 5 is a flow chart showing the entirety of an internal processing flow of Step S 1  of the processing procedure to be executed by the device of FIG.  1 . When the procedure is started, as shown in FIG. 3, the acyclic attributes are set at first Step S 1 _ 1  for all the nets in the object circuit. 
     Next, at Step S 1 _ 2 , the tracing is performed from the external clock pins to propagate the clock information till arrival at the input terminals of the elements of two or more inputs. Thus, the traced nets are set with the cyclic attributes. This is because the nets to the two or more inputs of the elements are naturally cyclic. 
     At Step S 1 _ 3 , the counter candidates are recognized, and at Step S 1 _ 4 , the attributes of the output signal nets of the elements having changed the attributes of the input signal nets are calculated to set the output signal nets of the elements with the calculated result. 
     At next Step S 1 _ 5 , it is decided whether or not the attributes of the input signal nets to the clock terminals of the flip-flops and the latches constructing the recognized counter attributes are acyclic. The routine shift to Step S 1   13    7 , if acyclic, but to Step S 1 _ 6  if not acyclic. 
     At Step S 1 _ 6 , the counter candidates, for which the attributes of the input signal nets to the clock terminals of the flip-flops and the latches are not acyclic, are recognized again as the counter, and all the input/output signal nets of the elements constructing the counter are set with the cyclic attributes. The routine shifts to Step S 1 _ 7 . 
     At Step S 1 _ 7 , it is decided whether or not there are nets having updated attributes. The routine shifts to Step S 1 _ 4 , if YES, but ends if NO. 
     FIG. 6 is a flow chart showing a flow of the internal operation of Step S 1 _ 3 . When the operation of Step S 1 _ 3  is started, all the flip-flops and latches in the object circuit are recognized at first Step S 1 _ 3 _ 1 , and their set is made into F. 
     Next, at Step S 1 _ 3 _ 2 , one of the flip-flops or the latches in the object circuit is taken out. At Step S 1 _ 3 _ 3 , a set T_f of the flip-flops and latches and a set T_c of the logic elements are set to empty sets. 
     Next, at Step S 1 _ 3 _ 4 , it is decided whether or not all the back traces from that terminal have been ended. The routine shifts to Step S 1 _ 3 _ 10 , if ended, but to Step S 1 _ 3 _ 6  if not. 
     At Step S 1 _ 3 _ 5 , the back traces are executed from the data input terminals and the set/reset terminals of the flip-flops or the latches, as taken out at Step S 1 _ 3 _ 2 . The back traces are to follow the signal paths backward of the signals to be fed to the terminals of the starting point. 
     At Step S 1 _ 3 _ 6 , the attributes of the net reached at the back tracing time are discriminated. The routine shifts to Step S 1 _ 3 _ 8 , if the counter attributes, to step S 1 _ 3 _ 9 , if the uncounter attributes, and to Step S 1 _ 3 _ 7  if neither the counter attributes nor the uncounter attributes. These counter attributes and uncounter attributes are attributes to be set at Step S 1 _ 3 _ 10 . 
     At Step S 1 _ 3 _ 7 , it is decided what of the power/ground, the external system reset terminals, the data output terminals of the flip-flops or the latches taken out at Step S 1 _ 3 _ 2 , the data output terminals of the flip-flops or the latches designated by the user, and the loops of the flip-flops or the latches and the logic elements the destination of the back trace belongs to. The routine shifts to Step S 1 _ 3 _ 8 , if YES, and to Step S 1 _ 3 _ 9  if NO. 
     At Step S 1 _ 3 _ 8 : the set of flip-flops and latches passed during the execution of the back trace is designated by T_f 1 , and the set T_f is replaced by T_fUT_f 1 ; the set of logic elements passed during the execution of the back trace is designated by T_c 1 , and the set T_c is replaced by T_cUT_c 1 ; and the routine shifts to Step S 1 _ 3 _ 4 . The sum of sets T_f and T_c, as obtained by repeating Steps S 1 _ 3 _ 5 , S 1 _ 3 _ 6 , S 1 _ 3 _ 7  and S 1 _ 3 _ 8 , is the counter candidate. 
     At Step S 1 _ 3 _ 9 : the set of flip-flops and latches passed during the execution of the back trace is designated by T_f 2 , and the set T_f is replaced by T_f 2 ; the set of logic elements passed during the execution of the back trace is designated by T_c 2 , and the set T_c is replaced by T_c 2 ; and the routine shifts to Step S 1 _ 3 _ 10 . 
     Next, at Step S 1 _ 3 _ 10 , the set F is replaced by F-T_f, the nets of T_f and T_c set at the branch from Step S 1 _ 3 _ 4  are set with the counter attributes whereas the nets of T_f and T_c set at the branch from Step S 1 _ 3 _ 9  are set with the uncounter attributes. 
     At Step S 1 _ 3 _ 11 , it is decided whether or not the set F is empty. The routine shifts to Step S 1 _ 3 _ 2 , if not empty, and is ended if empty. Thus, the elements of the counter attributes for the counter candidates are recognized. 
     FIG. 7 is a flow chart showing a flow of the internal operation of Step S 1 _ 4 . When the operation of Step S 1 _ 4  is started, one element having the attributes of the input signal net changed is taken at first Step S 1 _ 4 _ 1  from the object circuit. 
     Next, it is decided at Step S 1 _ 4 _ 2  whether or not the taken-out element is a one-input element. The routine shifts to Step S 1 _ 4 _ 3 , if the one-input element, but to Step S 1 _ 4 _ 4  if not. 
     At Step S 1 _ 4 _ 3 , the output signal net is set with the attributes of the input signal net, and the routine shifts to Step S 1 _ 4 _ 9 . 
     At Step S 1 _ 4 _ 4 , it is decided what of (1) elements with a to_clk flag (i.e., elements having outputs connected with the clock input terminal) raised, (2) elements with a to_data flag (i.e., elements having outputs connected with the data input terminal but not the to_clk flag raised) raised, and (3) the flip-flops/latches the element having changed the attributes of the input signal net belongs to. The routine shifts to Step S 1 _ 4 _ 6 , if (1), to Step S 1 _ 4 _ 5 , if (2), and to Step S 1 _ 4 _ 3  if (3). 
     At Step S 1 _ 4 _ 6 , for the elements having changed the attributes of the input signal net, the attributes of the output signal net are set cyclic, if all the attributes of the input signal net are cyclic, acyclic, if all are acyclic, semicyclic, if at least one cyclic attribute net and at least one acyclic attribute net are in the input signal net (if at least one input is the clock signal and if at least one input is data, for example), and semicyclic if at least one semicyclic attribute net but not any cyclic attribute net is in the input signal net. The routine shifts to Step S 1 _ 4 _ 9 . 
     At Step S 1 _ 4 _ 5 , it is decided whether or not the input signals of the elements having changed the attributes of the input signal net form a feedback path. The routine shifts to Step S 1 _ 4 _ 7 , if the feedback path is formed, but to Step S 1 _ 4 _ 6  if not. 
     At Step S 1 _ 4 _ 7 , it is decided whether or not the attributes of the net forming the feedback path with the input signals of the elements having changed the attributes of the input signal net are cyclic. The routine shifts to Step S 1 _ 4 _ 6 , if cyclic, but to Step S 1 _ 4 _ 8  if not. 
     At Step S 1 _ 4 _ 8 , the output signal net of that element is set with acyclic attributes, and the routine shifts to Step S 1 _ 4 _ 9 . 
     At Step S 1 _ 4 _ 9 , it is decided whether or not the element having changed the attributes of the input signal net is empty. The routine shifts to Step S 1 _ 4 _ 1 , if not empty, but is ended if empty. 
     FIG. 8 is a flow chart showing a flow of the internal operation of Step S 1 _ 4 _ 4 . When the operation of Step S 1 _ 4 _ 4  is started, the logic cone of the clock terminals and the set/reset terminals of the flip-flops and the latches in the object circuit is taken out at first at Step S 1 _ 4 _ 4 _ 1 . 
     Next, at Step S 1 _ 4 _ 4 _ 2 , the to_clk flag is raised for all the elements in the logic cone. This logic cone means a logic circuit in which the noted element is present up to the data output terminals of the flip-flops and the latches. 
     At Step S 1 _ 4 _ 4 _ 3 , it is decided whether or not all the flip-flops and the latches in the object circuit are processed. The routine shifts to Step S 1 _ 4 _ 4 _ 4 , if YES, but to Step S 1 _ 4 _ 4 _ 1  if NO. 
     At Step S 1 _ 4 _ 4 _ 4 , there are taken out the data terminals of the flip-flops and the latches and the logic cone in the object circuit. 
     Next, at Step S 1 _ 4 _ 4 _ 5 , the to_data flag is raised for all the elements having no to_clk flag raised in the logic cone. 
     At Step S 1 _ 4 _ 4 _ 6 , it is decided whether or not all the flip-flops and the latches in the object circuit have been processed. The routine shifts to Step S 1 _ 4 _ 4 _ 1 , if NO, but is ended if YES. 
     Here, the operations of Steps S 1 _ 4 _ 4 _ 4  and S 1 _ 4 _ 4 _ 5  in FIG. 8 can be replaced by those of FIG.  38 . 
     FIG. 9 is a flow chart showing a flow of the internal operation of Step S 1 _ 4 _ 4 _ 1 . When the operation of the Step S 1 _ 4 _ 4 _ 1  is started, the object terminal of the object element is recognized at first Step S 1 _ 4 _ 4 _ 1 _ 1  from the object circuit. 
     Next at Step S 1 _ 4 _ 4 _ 1 _ 2 , the element having the output signal net connected with that terminal is taken out. 
     At Step S 1 _ 4 _ 4 _ 1 _ 3 , the back trace is executed from the input terminal of the element taken out at the preceding Step, till arrival at the data output terminals of the flip-flops and the latches, to construct a circuit of the traced element and its connection information and to store it as the logic cone, and the operation is ended. 
     FIG. 10 is a flow chart showing a flow of the internal operation of Step  3 . When the operation of Step S 3  is started, at Step S 3 - 1 , the flip-flop and the latch, for which the net of the acyclic attributes is the input signal of the clock terminal, are recognized from the object circuit, and the operation is ended by raising the dynamic timing analysis flag for that element. 
     FIG. 11 is a flow chart showing a flow of the internal operation of Step S 4 . When the operation of Step S 4  is started, at Step S 4 _ 1 , a gated clock  1  flag is raised for the logic element having the to_clk flag raised and having the output signal net of the cyclic attributes whereas a gated clock  2  flag is raised for the logic element in the logic cone, as having the output signal net of the semicyclic attributes, and the operation is ended. 
     FIG. 12 is a flow chart showing a flow of the internal operation of Step S 2 . When the operation of Step S 2  is started, at first Step S 2 _ 1 , what has an input signal as totally two or more nets of the cyclic or semicyclic attributes is recognized from the object circuit. 
     Next, it is decided at Step S 2 _ 2  whether or not a clock selecting logic flag is raised at that element. The routine shifts to Step S 2 _ 3 , if raised, but to Step S 2 _ 4  if not. 
     At Step S 2 _ 3 , it is confirmed by the user whether or not the circuit is designed to act normally without any problem even if the element having the clock selecting logic flag raised outputs a hazard at the time of switching the clock. If not, the dynamic timing analysis flag is raised for that element. 
     At Step S 2 _ 4 , it is confirmed by the user whether or not the element constructs the clock selecting logic. The routine shifts to Step S 2 _ 5 , if constructed, but to Step S 2 _ 6  if not. 
     At Step S 2 _ 6 , it is decided whether or not all the elements are checked. The routine shifts to Step S 2 _ 1 , if not, but the operation is ended if checked. 
     FIG. 13 is a flow chart showing a flow of the internal operation of Step S 2 _ 2 . When the operation of Step S 2 _ 2  is started, at first Step S 2 _ 2 _ 1 , the element having totally two or more nets of the cyclic attributes or semicyclic attributes are inputted is recognized from the object circuit. 
     Next, at Step S 2 _ 2 _ 2 , it is decided whether or not the recognized element is the selecting logic element of a multiplexer or the like and whether or not the net of the cyclic attributes or semicyclic attributes constructs the selecting logic. The routine shifts to Step S 2 _ 2 _ 3 , if the selecting logic is constructed, but to Step S 2 _ 2 _ 4  if not. 
     At Step S 2 _ 2 _ 3 , the clock selecting logic flag is raised for the element constructing the selecting logic. 
     At Step S 2 _ 2 _ 4 , the back trace is executed from the semicyclic input terminals of that element till arrival at the data output terminals of the flip-flops or the latches or the element having the nets of both the cyclic attributes and the acyclic attributes connected with their input terminals, to construct a circuit of the traced elements and their connection information. 
     At Step S 2 _ 2 _ 5 , it is decided whether or not the back trace arrives at the data output terminals of the flip-flops or the latches. The routine shifts to Step S 2 _ 2 _ 6 , if YES, but to Step S 2 _ 2 _ 7  if NO. 
     Next, at Step S 2 _ 2 _ 6 , a clock selecting logic candidate flag is raised for the individual elements constructing that circuit. 
     Next, at Step S 2 _ 2 _ 7 , the individual acyclic input signal nets in that circuit are back-traced till arrival at the data output terminals of the flip-flops or the latches, to construct the individual logic functions and calculate the OR and AND thereby to check exclusiveness of the individual acyclic input signals. 
     At Step S 2 _ 2 _ 9 , it is decided whether or not the individual acyclic input signals are exclusive. The routine shifts to Step S 2 _ 2 _ 6 , if not, but to Step S 2 _ 2 _ 3  if exclusive. 
     At Step S 2 _ 2 _ 10 , it is decided whether or not all the object elements are checked. The routine shifts to Step S 2 _ 2 _ 1 , if not, but is ended if checked. 
     FIG. 14 is a flow chart showing a flow of the internal operation of Step S 6 . When the operation of step S 6  is started, at first Step S 6 _ 1 , there is constructed from the object circuit an element net list of elements constructing the counter, the elements having the gated clock  1  flag raised, and the elements having the gated clock  2  flag raised. 
     At next Step S 6 _ 2 , there are determined points in the net list to be dumped by the logic simulator for forming the clock waveforms. 
     At Step S 6 _ 3 , the input signals of the elements having the cyclic attribute net inputted and the semicyclic attribute net outputted, i.e., the elements having no clock selecting logic flag raised are so fixed as to propagate the cyclic attributes. 
     At Step S 6 _ 4 , it is decided whether or not the elements having the cyclic attribute net inputted and the semicyclic attribute net outputted, i.e., the elements having no clock selecting logic flag disappear. The routine shifts to Step S 6 _ 5 , if YES, but again to Step S 6 _ 4  if NO. 
     At Step S 6 _ 5 , the external clock terminals, the set/reset signals and the input pattern to the elements having the clock selecting logic flag raised are used to execute the logic simulation thereby to prepare the waveform information from the simulation result at the points to be dumped. 
     At Step S 6 _ 6 , it is decided by using the input signal of the minimum pulse width as the clock whether or not other input signals are multi-cycle paths, as seem from the clocks fed to the flip-flops or the latches outputting the input signal, with respect to the elements having the gated clock  1  flag raised and the acyclic attributes nets connected with the inputs. If, it is recognized what cycle transfers, and the operation is ended. Here, this Step S 6 _ 6  can be omitted. This is because the waveform information obtained in the simulation of the foregoing Step S 6 _ 5  may be utilized. 
     FIG. 15 is a flow chart showing a flow of the internal operation of Step S 6 _ 2 . When the operation of Step S 6 _ 2  is started, the elements of two or more inputs having the to-clk flag raised is taken out at first Step S 6 _ 2 _ 1 . 
     At next Step S 6 _ 2 _ 2 , it is decided whether or not the gated clock  1  flag is raised for that element. The routine shifts to Step S 6 _ 2 _ 3 , if raised, but to the operation of Step S 6 _ 2 _ 4  if not. 
     At Step S 6 _ 2 _ 3 , the input signals and the output signals of that element are used as the gated clock analyzing dump points, and the routine shifts to Step S 6 _ 2 _ 7 . 
     At Step S 6 _ 2 _ 4 , it is decided whether or not the gated clock  2  flag is raised for that element. The routine shifts to step S 6 _ 2 _ 5 , if raised, but to Step S 6 _ 2 _ 6  if not. 
     At Step S 6 _ 2 _ 5 , if the input signal net of that element has cyclic attributes, the input signal of the cycle attributes is used as the dump point for generating the clock waveform, and the routine shifts to Step S 6 _ 2 _ 6 . 
     At Step S 2 _ 6 _ 8 , it is decided whether or not all the object elements are checked. The routine shifts to Step S 6 _ 2 _ 7 , if checked, but to Step S 6 _ 2 _ 1  if not. 
     At Step S 6 _ 2 _ 6 , the routine is ended by using as the dump point the output signals of the flip-flops and the latches having no output signal propagated to the elements of two or more inputs and the to_clk flag raised and having the cyclic or semicyclic attribute nets connected with the output terminals. 
     FIG. 16 is a flow chart showing a flow of the internal operation of Step S 7 . When the operation of Step S 7  is started, at first Step S 7 _ 1 , there is recognized the logic cone from the object circuit to the clock terminals and the set/reset terminals of the asynchronous flip-flops and the asynchronous latches which are connected with the clock terminals of all the flip-flops and the latches outputting signals to the logic cone and at which the signal net has the cyclic attributes or semicyclic attributes. 
     Next, at Step S 7 _ 2 , it is decided whether or not only one signal of the maximum operating frequency is in the signals to the clock terminals of all the flip-flops and the latches outputting the signals to the logic cone. The routine shifts to Step S 7 _ 3 , if only one, but to Step S 7 _ 4  if two or more. 
     At Step S 7 _ 3 , the data output terminals of the flip-flops or the latches fed with the clock of the maximum operating frequency are set with the inverted/uninverted clocks of a duty of 50% having a twice cycle of the maximum operating frequency, and the signal attribute calculation S 1 _ 4  is executed. The recognition S 4  of the clock gate is executed, and the routine then shifts to Step S 7 _ 5 . 
     At Step S 7 _ 5 , it is examined, with respect to the data transfer path between the flip-flops or the latches to be fed with a newly defined clock and the flip-flops or the latches for transferring data with the former flip-flops or the latches, whether the clock for the most strict setup/hold conditions is inverted or uninverted. The examination result is stored in the storage unit  6 , and the routine shifts to Step S 7 _ 4 . 
     At Step S 7 _ 4 , it is decided whether or not all the logic cones to the clock terminals of the asynchronous flip-flops and the asynchronous latches are checked. The routine shifts to Step S 7 _ 1 , if not checked, but is ended if checked. 
     FIG. 17 is a flow chart showing a flow of the internal operation of Step S 5 . When the operation of Step S 5  is started, at first Step S 5 _ 1 , there is admitted the passage of an in-element path from the clock terminals of the flip-flops and the latches for which the data output signal net has the cyclic or semicyclic attributes. Then, the clock information is propagated from the external clock signals by tracing the elements for which the aforementioned in-element path has been recognized and for which the gated clock  1  flag and the gated clock  2  flag are raised. On the basis of the information of the clock selecting logic, graphs are made to join the individual dump points of the number of combinations of the output clocks of the possible clock selecting logic. 
     Next, at Step S 5 _ 2 , for the individual graphs, the flip-flops and the latches, for which the graph apexes are the clock sources, are recognized, and the data transfer path with the flip-flops and the latches, for which the graph apexes are not the clock sources, if any, are extracted as the asynchronous transfer path. Then, the operation is ended. 
     FIG. 18 is a flow chart showing a flow of the internal operation of Step S 8 . When the operation of Step S 8  is started, the element having the gated clock  2  flag raised is taken out at first Step S 8 _ 1  . 
     Next, at Step S 8 _ 2 , it is decided whether the element has two inputs or three inputs or has the rear stage connected with the element having one input. The routine shifts to Step S 8 _ 4 , if not any, but to Step S 8 _ 3  if any. 
     At Step S 8 _ 4 , a dynamic timing analysis flag is raised for that element, and the routine shifts to Step S 8 _ 3 . 
     At Step S 8 _ 3 , it is decided whether or not all the elements having the gated clock  2  flag raised are checked. The routine shifts to Step S 8 _ 1 , if not checked, but is ended if checked. 
     Here in the description thus far made, it is premised that the circuit restriction input unit  3  has such a circuit restriction on the circuit construction of the clock gate that the element having the gated clock  2  flag raised is the two-input element or the three-input element having a rear stage connected with the one-input element. 
     FIG. 19 is a flow chart showing another flow of the internal operation of Step S 8 . When the operation of Step S 8  is started, the tristate element is taken out at first Step S 8 _ 5 . Next, at Step S 8 _ 6 , the logic cone to the enable terminal of that element is recognized. 
     At Step S 8 _ 7 , it is decided whether or not a cyclic or semicyclic net is in the input signal net to that logic cone. The routine shifts to Step S 8 _ 8 , if YES, but to Step S 8 _ 9  if NO. 
     At Step S 8 _ 8 , it is confirmed by the user whether or not the output signal of the tristate element is latched for every cycles. If the circuit is constructed to latch for every cycles, the dynamic timing analysis flag is raised for that tristate element. 
     At Step S 8 _ 9 , it is decided whether or not two or more logic elements are in that logic cone. The routine shifts to Step S 8 _ 10 , if YES, but to Step S 8 _ 11  if NO. 
     At Step S 8 _ 10 , the dynamic timing analysis flag is raised for the tristate element, and the routine shifts to Step S 8 _ 11 . 
     At Step S 8 _ 11 , it is decided whether or not all the tristate elements in the object circuit are checked. The routine shifts to Step S 8 _ 5 , if not checked, but is ended if checked. 
     Here in the description thus far made, it is premised that the circuit restriction input unit  3  has such a circuit restriction on the circuit construction of the logic cone to the enable terminals of the tristate element that the logic element of two or more inputs must not be in the logic cone, and that the output signal of the tristate element does not take a high impedance even if the data are not held in the output signal net by a bus holder circuit (e.g., a bus repeater circuit such as a latch circuit constructed of two inverters). 
     FIG. 39 shows still another flow chart of the internal operation of the aforementioned Step S 8 . When the operation of Step S 8  is started, the flip-flops and the latches are taken out at first Step S 8 _ 12 . Next, at Step S 8 _ 13 , the logic cone to the set/reset terminals of the element is recognized. 
     At Step S 8 _ 14 , it is decided whether or not the attributes of the net connected with the set/reset terminals of the element are acyclic. The routine shifts to Step S 8 _ 15 , if acyclic, but to Step S 8 _ 17  if not. 
     At Step S 8 _ 15 , it is decided whether or not a logic element of two or more inputs is in the logic cone. The routine shifts to Step S 8 _ 17 , if YES, but to Step S 8 _ 16  if NO. 
     At Step S 8 _ 16 , the dynamic timing analysis flag is raised for the flip-flops or the latches, and the routine shifts to Step S 8 _ 17 . 
     At Step S 8 _ 17 , it is decided whether or not all the flip-flops and the latches in the object circuit are checked. The routine shifts to Step S 8 _ 12 , if not, but is ended if checked. 
     Here in the description of the FIG. 39, it is premised that the circuit restriction input unit  3  has such a circuit restriction on the circuit construction of the logic cone to the set/reset terminals of the flip-flops and the latches either that the attributes of the net connected with the set/reset terminals of the element are not acyclic or that the logic cone is constructed of only zero or more one-input element. 
     FIG. 20 is a flow chart showing a flow of the internal operation of Step S 9 . When the operation of step  9  is started, at first Step S 9 _ 1 , there is taken out the element which has the gated clock  2  flag raised and at least one acyclic attribute signal connected with the input signal net. 
     At Step S 9 _ 2 , such input signals to the element as have semicyclic attributes are back-traced to extract and substitute the net of the cyclic attributes for the cyclic attribute signals, and the cycle of the input cyclic attribute signals is set to a T_cycle. 
     At Step S 9 _ 3 , such ones of the input signals to the element as have the acyclic attributes are back-traced till arrival at the data output terminals of the flip-flops and the latches to take out the signals to the clock terminals of the destination flip-flops and latches. 
     At Step S 9 _ 4 , it is decided whether or not the taken-out signals have the cyclic attributes. The routine shifts to Step S 9 _ 5 , if YES, but to Step S 9 _ 6  if NO. 
     At Step S 9 _ 5 , the cycle of the signals of the cyclic attributes is set to the T_acycle, and the routine shift to Step S 9 _ 9 . At Step S 9 _ 6 , it is decided whether or not the taken-out signals have the semicyclic attributes. The routine shifts to Step S 9 _ 7 , if YES, but to Step S 9 _ 8  if NO. 
     At Step S 9 _ 7 , the semicyclic attributes are back-traced to extract the net of the cyclic attributes and to substitute it for the cyclic attribute signals. The cycle of these cyclic attribute signals is set to the T_acycle, and the routine advances to Step S 9 _ 9 . 
     At Step S 9 _ 9 , it is decided whether or not a relation of 2×T_acycles≧T_cycles holds for the combination of the T_cycles and the T_acycles. The input acyclic signal path defining the T_acycles for the relation, that is, the data transfer path between the acyclic attribute signals of the elements taken out at Step S 9 _ 1  and the flip-flops and the latches reached by the back trace of Step S 9 _ 3  may be a multicycle path. Therefore, the user&#39;s confirmation is requested, and the routine shifts to Step S 9 _ 8 . 
     At Step S 9 _ 8 , it is decided whether or not all the elements in the object circuit, in which at least one acyclic attribute signal having the gated clock  2  flag raised is inputted to the input signal net, are checked. The routine shifts to Step S 9 _ 1 , if not checked, but is ended if checked. 
     FIG. 21 is a flow chart showing a flow of the internal operation of Step S 10 . When the operation of Step S 10  is started, the element having the gated clock  1  flag raised is taken out at first Step S 10 _ 1 . 
     At Step S 10 _ 2 , it is decided whether or not two or more cyclic attribute signals of the identical waveforms are inputted to the element. The routine shifts to Step S 10 _ 3 , if inputted, but to Step S 10 _ 4  if not. 
     At Step S 10 _ 3 , the dynamic timing analysis flag is raised for that element, and the routine shifts to Step S 10 _ 7 . This is because there is a fear of hazard if it is decided at Step S 10 _ 2  that two or more cyclic attribute signals of the identical waveforms are inputted. 
     At Step S 10 _ 4 , it is determined that either or both of the setup restriction check and the hold restriction check are to be executed on the basis of the logic simulation result of the gated clock analyzing dump points. 
     At Step S 10 _ 5 , the gated clock analysis is executed by the static timing analysis. At Step S 10 _ 6 , it is decided whether or not the setup restriction or the hold restriction is violated. The routine shifts to Step S 10 _ 3 , if YES, but to Step S 10 _ 7  if NO. 
     At Step S 10 _ 7 , it is decided whether or not all the elements having the gated clock  1  flag raised in the object circuit are checked. The routine shifts to Step S 10 _ 1 , if not checked, but is ended if checked. 
     FIG. 22 is a flow chart showing another flow of the internal operation of Step S 10 . When the operation of Step S 10  is started, the element having the gated clock  2  flag raised is taken out at first Step S 10 _ 8 . 
     At Step S 10 _ 9 , such ones of the input signals to that element as have the semicyclic attributes are back-traced to extract and substitute the cyclic attribute signals for the back-traced signals. 
     At Step S 10 _ 10 , it is decided whether or not two or more cyclic attribute signals of the identical waveforms are inputted to that element. The routine shifts to Step S 10 _ 11 , if inputted, but to Step S 10 _ 12  if not. 
     At Step S 10 _ 11 , the dynamic timing analysis flag is raised for that element, and the routine shifts to Step S 10 _ 15 . This is because there is a fear of hazard if it is decided at Step S 10 _ 10  that two or more cyclic attribute signals of the identical waveforms are inputted. 
     At Step S 10 _ 12 , it is determined that either or both of the setup restriction check and the hold restriction check are to be executed on the basis of the logic simulation result of the gated clock analyzing dump points. 
     At Step S 10 _ 13 , the gated clock analysis is executed by the static timing analysis device. At Step S 10 _ 14 , it is decided whether or not the setup restriction or the hold restriction is violated. The routine shifts to Step S 10 _ 11 , if YES, but to Step S 10 _ 15  if NO. 
     At Step S 10 _ 15 , it is decided whether or not all the elements having the gated clock  2  flag raised in the object circuit are checked. The routine shifts to Step S 10 _ 8 , if not checked, but is ended if checked. 
     At the forgoing Step S 12 , the following operations are executed, although their detailed steps are not shown. 
     Specifically, it is recognized that the circuit (logic) for feeding its output to the asynchronous reset terminal or the asynchronous set terminal of the flip-flop or the latch is controlled by the clock signal. 
     When the control by the clock signal is recognized, it is decided at Step S 10  whether or not the dynamic timing analysis flag is raised. At this Step, therefore, it is not especially decided whether or not the dynamic timing analysis flag is raised. 
     On the other hand, it is recognized whether or not a signal at a fixed value is fed to the circuit (logic) for feeding its output to the asynchronous reset terminal or the asynchronous set terminal of the flip-flop or the latch, or whether or not a node to be fed with the signal of the fixed value is in that circuit. 
     When the signal of the fixed value is neither fed nor is in the circuit the node to be fed with the signal of the fixed value, the output of the circuit is determined by the input signal thereto so that the dynamic timing analysis flag is raised for that flip-flop or the latch. 
     When the signal of the fixed value is fed or when the node to be fed with the signal of the fixed value is in the circuit, it is recognized whether or not the fixed value is propagated to the asynchronous reset terminal or the asynchronous set terminal. 
     When it is recognized that the fixed value is propagated to the asynchronous reset terminal or the asynchronous set terminal, the dynamic timing analysis flag is not raised for that flip-flop or the latch. When it is recognized that the fixed value is not propagated to the asynchronous reset terminal or the asynchronous set terminal, on the contrary, the signal to be fed to the asynchronous reset terminal or the asynchronous set terminal is determined by the signal fed to that circuit. In this case, therefore, the dynamic timing analysis flag is raised for that flip-flop or the latch. 
     FIG. 23 is a flow chart showing a flow of the internal operation of Step S 11 . When the operation of the Step S 11  is started, at first Step S 11 _ 1 , the dynamic timing analysis applying circuit is recognized from the dynamic timing analysis flag. 
     Next, at step S 11 _ 2 , there is constructed a sum of sets of dynamic timing analysis applying circuit having no empty product of sets. At Step S 11 _ 3 , the product of sets between the individual unions and the individual logic hierarchies is calculated. 
     At Step S 11 _ 4 , it is decided whether or not all the dynamic timing analysis applying circuits in the object circuit are checked. The routine shifts to Step S 11 _ 5 , if checked, but to Step S 11 _ 1  if not. 
     At Step S 11 _ 5 , the ratio of dynamic timing analysis applying circuits in the individual logic hierarchies is calculated. At Step S 11 _ 6 , it is decided whether or not there is a logic hierarchy having a ratio of 100%. The routine shifts to Step S 11 _ 7 , if YES, but to Step S 11 _ 8  if NO. 
     At Step S 11 _ 7 , the logic hierarchy operation is used as the dynamic timing analysis applying hierarchy, and the routine shifts to Step S 11 _ 8 . 
     At Step S 11 _ 8 , the dynamic timing analysis is executed by the dynamic timing analyzing device, and the routine is then ended. 
     Here, FIG. 23 shows a processing flow of the case in which the operations of Steps S 10 _ 5  and S 10 _ 6  of FIG.  20  and Steps S 10 _ 12  and S 10 _ 13  of FIG. 21 are not executed. When these operations of Steps S 10 _ 5  and S 10 _ 6  of FIG.  20  and Steps S 10 _ 12  and S 10 _ 13  of FIG. 21 are to be executed, the operations of Steps S 11 _ 1 _ 5 , S 11   —1 _ 6 , S 11 _ 1 _ 7  and S 11 _ 1 _ 8  are not executed of FIG.  23 . 
     FIG. 24 is a flow chart showing a flow of the internal operation of Step S 11 _ 1 . When the operation of Step S 11 _ 1  is started, at first Step S 11 _ 1 _ 1 , the element having the dynamic timing analysis flag raised is taken out. 
     At Step S 11 _ 1 _ 2 , it is decided what of the following elements that element belongs to: (1) the logic elements in the logic cone to the flip-flops or the latches or the data input terminals or the set/reset terminals of the flip-flops or the latches; and (2) the logic elements in the logic cone to the clock terminals of the flip-flops or the latches. The routine shifts to step S 11 _ 1 _ 3 , if (1), but to Step S 11 _ 1 _ 4  if (2). 
     At Step S 11 _ 1 _ 3 , the path between the data output terminals and the set/reset terminals, i.e., the path in the flip-flop and the latch is made passable at the trace executing time so that the back trace is executed till arrival from the input terminals of the element to the data output element of the flip-flop and so that the forward trace is executed till arrival at the data input terminal of the flip-flop from the output terminal of the element.  10  The elements having been passed by those traces and the destination flip-flop are used as the dynamic timing analysis applying circuit, and the routine shifts to Step S 11 _ 1 _ 9 . 
     At Step S 11 _ 1 _ 4 , the elements obtained by executing Step S 11 _ 1 _ 3  are used as the dynamic timing analysis applying circuit  1 , and the sum of sets of those elements and the elements obtained by executing the Step S 11 _ 1 _ 3  for the flip-flops and the latches having the clock terminals reached by tracing and propagating the output signals of the elements is used as the dynamic timing analysis applying circuit  2 . 
     At Step S 11 _ 1 _ 5 , the dynamic timing analysis is executed for the dynamic timing analysis applying circuit  1 . At Step S 11 _ 1 _ 6 , it is decided whether or not a hazard has occurred in the output signals of the element in the dynamic timing analysis applying circuit  1 . The routine shifts to Step S 11 _ 1 _ 7 , if YES, but to Step S 11 _ 1 _ 8  if NO. 
     At Step S 11 _ 1 _ 7 , only the dynamic timing analysis applying circuit  2  is used as the dynamic timing analysis applying circuit, and the routine shifts to Step S 11 _ 1 _ 9 . 
     At Step S 11 _ 1 _ 8 , the dynamic timing analysis applying circuits  1  and  2  are deleted. 
     At Step S 11 _ 1 _ 9 , it is decided whether or not all the elements, for which the dynamic timing analysis flag is raised, in the object circuit are checked. The routine shifts to Step S 11 _ 1 _ 1 , if not checked, but is ended if checked. 
     FIG. 25 is a flow chart showing a flow of the internal operation of Step S 11 _ 8 . When the operation of Step S 11 _ 8  is started, at Step S 11 _ 8 _ 1 , the elements composing the union of the dynamic timing analysis applying circuit having no empty product of set and their connection information are constructed to execute the dynamic timing analysis by using the input pattern, and the routine is ended. 
     FIG. 26 is a flow chart showing another example of the flow of the internal operation of Step S 11 _ 8 . At Step S 11 _ 8 _ 1 , delay information is fed to the elements and net constructing the dynamic timing analysis applying circuit and all the elements and nets on the clock tree to the clock terminals of the flip-flops and the latches in the dynamic timing analysis applying circuit. 
     Next, at Step S 11 _ 8 _ 2 , in order to transfer data to the flip-flops and the latches in the dynamic timing analysis non-applying circuit for transferring data with the flip-flops constructing the boundary of the dynamic timing analysis applying circuit, there is adjusted the delay value of all the elements of the nets on the clock tree to the flip-flops and the latches in the dynamic timing analysis non-applying circuit for transferring data with the flip-flops constructing the boundary of the dynamic timing analysis applying circuit. The routine is ended after the dynamic timing analysis was executed at Step S 11 _ 8 _ 3 . 
     &lt;&lt;Example of Processing Specific Object circuit&gt;&gt; 
     A specific example of the operation by the counter candidate recognition S 1 _ 3  will be described by taking up one example of the object circuit. FIG. 27 is a circuit diagram showing one example of the object circuit. This object circuit is provided with: an external input pin DIN to be fed with a data signal from the outside; an external input pin ENABLE to be fed with an enable signal from the outside; an external input pin RST to be fed with a reset signal from the outside; an external input pin CLK to be fed from a clock signal from the outside; and an external output pin DOUT for outputting the data signal to the outside. 
     Elements G 1 , G 2 , G 3  and G 4  are all the logic elements, and elements FF 1 , FF 2 , FF 3 , FF 4 , FF 5  and FF 6  are all flip-flops. At first Step S 1 _ 3 _ 1 , the storage unit  5  is stored with the table of the set of F={FF 1 , FF 2 , FF 3 , FF 4 , FF 5  and FF 6 } of the flip-flops and the latches in the object circuit. 
     Next, at Step S 1 _ 3 _ 2 , the flip-flop FF 1  is taken out from the set F. At step S 1 _ 3 _ 3 , the set of the flip-flops and the latches traced at and after Step S 1 _ 3 _ 4  is designated by T_f, and the set of the logic elements is designated by T_c. These individual sets are emptied and stored in the storage unit  5 . 
     When the back trace is executed at Step S 1 _ 3 _ 5  from the data input terminal d of the FF 1 , the data output terminals q of the element G 1  and the flip-flops FF 2  and FF 1  are reached. When the back trace is executed from a reset terminal sdn of the FF 1 , the flip-flop FF 3  designated by the user is reached. 
     When the branching is made at Step S 1 _ 3 _ 6  by the aforementioned reached net attributes, the attributes are neither those of the counter nor those of the uncounter, so that the routine shifts to Step S 1 _ 3 _ 7 . 
     When the branching by the destination is executed at Step S 1 _ 3 _ 7 , the destination is the data output terminal q of the FF 1  and the flip-flop FF 3  designated by the user so that the routine shifts to Step S 1 _ 3 _ 8 . 
     Next, at Step S 1 _ 3 _ 8 , T_f={FF 1 , FF 2 } and T_c={G 1 }, and these are stored in the storage unit  5 . 
     At Step S 1 _ 3 _ 10 , F={FF 3 , FF 4 , FF 5 , FF 6 }, and the counter attributes are set for the net of T_f and T_c and stored in the storage unit  5 . At Step S 1 _ 3 _ 11 , the set F is not empty so that the routine shifts to Step S 1 _ 3 _ 2 . 
     Next, at Step S 1 _ 3 _ 2 , the set F is taken out from the FF 5 . At Step S 1 _ 3 _ 3 , the set of the flip-flops and the latches to be traced at and after Step S 1 _ 3 _ 5  is designated by T_f, and the set of the logic elements is designated by T_c. These sets are made empty and stored in the storage unit  5 . 
     When the back trace is executed at Step S 1 _ 3 _ 5  from the data input terminal d of the FF 5 , there are recognized: the path to reach the element G 3  and the data output terminals q of the FF 5 , the path to reach the element G 3 , the FF 4 , the G 2  and the data output terminal q of the FF 5 , and the path to reach the counter attribute net connected with the output terminals of the elements G 3 , FF 4 , G 2  and FF 1 . 
     The branching is executed at Step S 1 _ 3 _ 6  and Step S 1 _ 3 _ 7 , and the routine shifts to Step S 1 _ 3 _ 7 . At Step S 1 _ 3 _ 8 , T_f={FF 4 , FF 5 } and T_c={G 3 , G 2 }, and these sets are stored in the storage unit  5 . 
     At Step S 1 _ 3 _ 10 , F={FF 3 , FF 6 }, and the counter attributes are set for the net of T_f and T_c and stored in the storage unit  5 . At Step S 1 _ 3 _ 11 , the set F is not empty so that the routine shifts to Step S 1 _ 3 _ 2 . 
     When the operation of Step S 1 _ 3  is executed for the FF 3  and the FF 6 , the destinations of the individual back traces are the external terminals. Thus, the routine shifts to Step S 1 _ 3 _ 10  through Step S 1 _ 3 _ 9  to set the uncounter attributes, and the routine is ended. 
     A specific example of the operation by the attribute calculation S 1 _ 4  will be described by taking up another example of the object circuit. FIG. 28 is a circuit diagram showing one example of the object circuit. In this object circuit: the net connected with the cp terminals of the elements FF 1  and FF 2  has the cyclic attributes; the net connected with the al terminal of the element G 1  has the cyclic attributes; the net connected with the a 2  terminal of the element G 1  has acyclic attributes; and the net connected with the a 2  terminal of the element G 2  has the cyclic attributes. 
     Both the elements G 1  and G 2  are the logic elements, and all the elements FF 1 , FF 2  and FF 3  are the flip-flops. The to_clk flag is raised for the element G 1 , and the to_data flag is raised for the element G 2 . On the other hand, it is assumed that the attributes of the input signals to the a 1  terminal of the element G 1  and the a 2  terminal of the element G 2  are changed. 
     At first Step S 1 _ 4 _ 1 , the elements G 1  and G 2  having the input signal attributes changed are recognized and stored in the storage unit  5 . At Step S 1 _ 4 _ 2 , it is decided whether or not the elements G 1  and G 2  are the one-input element. The routine shifts to Step S 1 _ 4 _ 4  because they are not the one-input element. 
     At Step S 1 _ 4 _ 4 , the flags of the elements G 1  and G 2  are judged. The element Gi has the to_clk flag raised so that the routine shifts to Step S 1 _ 4 _ 6 , and the element G 2  has the to_data flag raised so that the routine shifts to Step S 1 _ 4 _ 5 . 
     At Step S 1 _ 4 _ 5 , it is decided whether or not the input signal of the element G 2  forms a feedback path. Since the signal to the a 3  terminal of the element G 2  forms the feedback path, the routine shifts to Step S 1 _ 4 _ 7 . 
     Next at Step S 1 _ 4 _ 7 , the net net 1  connected with the a 3  terminal of the element G 2  forming the feedback path is set to the acyclic attributes at the first Step S 1 _ 1  of the recognition S 1  of the clock information so that the routine shifts to Step S 1 _ 3 _ 8 . 
     At Step S 1 _ 3 _ 8 , the net net 3  connected with the output signal of the element G 2  is set to have the acyclic attributes, which are stored in the storage unit  5 , and the routine shifts to Step S 1 _ 4 _ 9 . 
     At Step S 1 _ 4 _ 6 , on the other hand, the net connected with the a 1  input terminal of the element G 1  has the cyclic attributes, and the net connected with the a 2  input terminal has the acyclic attributes. 
     Therefore, the net net 2  connected with the output signal of the element G 1  is set to have the duasi-periodic attributes, which are stored in the storage unit  5 , and the routine shifts to Step S 1 _ 4 _ 9 . 
     At Step S 1 _ 4 _ 9 , it is decided whether or not there is an element having changed the attributes of the data input signal net. In the case of this circuit example, no element has changed the attributes of the data input signal net so that the routine is ended. 
     A specific example of the operation by the attribute calculation S 1 _ 4  will be described by taking up another example of the object circuit. FIG. 29 is a circuit diagram showing one example of the object circuit. In this object circuit, the signals to the a 2  terminal of the element G 1 , the a 1  terminal of the element G 2 , the a 1  and a 2  terminals of the element G 3 , and the a 1  and a 2  terminals of the element G 6  are those from the data output terminals of the flip-flops or the latches. 
     All the elements G 1 , G 2 , G 3 , G 4 , G 5  and G 6  are the logic elements, and both the elements FF 1  and FF 2  are the flip-flops. 
     At first Step S 1 _ 4 _ 4 _ 1 , the logic cone to the cp terminals of the FF 1  and FF 2  is recognized and stored in the storage unit  5 . In the case of this circuit diagram, the logic cone to the cp terminals of the FF 1  and FF 2  is a circuit composed of the elements G 1 , G 2  and G 3 . 
     At Step S 1 _ 4 _ 4 _ 2 , the to_clk flag is raised for the elements G 1 , G 2  and G 3  and stored in the storage unit  5 . 
     At Step S 1 _ 4 _ 4 _ 3 , it is decided whether or not all the flip-flops and the latches in the object circuit are processed. Since all of these are processed, the routine shifts to Step S 1 _ 4 _ 4 _ 4 . 
     At Step S 1 _ 4 _ 4 _ 5 , the logic cone to the d terminals of the FF 2  is recognized and stored in the storage unit  5 . In the case of this circuit diagram, the logic cone to the d terminal of the FF 2  is a circuit composed of the elements G 3 , G 4 , G 5  and G 6 . 
     Next, at Step S 1 _ 4 _ 4 _ 6 , the to_data flag is raised for the elements G 4 , G 5  and G 6  having no to_clk flag raised and is stored in the storage unit  5 . 
     At Step S 1 _ 4 _ 4 _ 3 , it is decided whether or not all the flip-flops and the latches in the object circuit are processed. Since this answer is YES, the routine is ended. 
     A specific example of the operation by the attribute calculation S 1 _ 4 _ 4 _ 1  will be described by taking up another example of the object circuit. FIG. 30 is a circuit diagram showing one example of the object circuit. In this object circuit, the signals to the a 1  and a 2  terminals of the element G 3 , the a 1  terminal of the element G 5 , the a 1  and a 2  terminals of the element G 6  are those coming from the data output terminals of the flip-flops or the latches. 
     All the elements G 1 , G 2 , G 3 , G 4 , G 5  and G 6  are the logic elements. At first Step S 1 _ 4 _ 4 _ 1 _ 1 , the a 1  terminal of the element G 1  is recognized and stored in the storage unit  5 . 
     At Step S 1 _ 4 _ 4 _ 1 _ 2 , the element G 2  connected with the a 1  terminal of the element G 1  is recognized and stored in the storage unit  5 . 
     At Step S 1 _ 4 _ 4 _ 1 _ 3 , the back trace is executed from the a 1  terminal of the element G 2  to take out the element G 3 . Since the signals to the a 1  and a 2  terminals of the element G 3  are those coming from the data output terminals of the flip-flops or the latches, the back trace is executed from the a 2  terminal of the element G 2  to take out the element G 4 . Since the signal to the a 1  terminal of the element G 4  is that coming from the data output terminal of the flip-flop or the latch, the back trace is executed from the a 2  terminal of the element G 4  to take out the element G 5 . Since the signal to the a 1  terminal of the element G 5  is that coming from the data output terminal of the flip-flop or the latch, the back trace is executed from the a 3  terminal of the element G 4  to take out the element G 6 . Since the signal to the a 1  terminal of the element G 6  is that coming from the data output terminal of the flip-flop or the latch, the back trace is ended to construct the circuit composed of the elements G 2 , G 3 , G 4 , G 5  and G 6  obtained by the trace result. This circuit is stored in the storage unit  5  as the logic cone to the a 1  terminal of the element G 1 , and the routine is ended. 
     A specific example of the operation by the clock selecting logic flag S 2 _ 2  will be described by taking up another example of the object circuit. FIG. 31 is a circuit diagram showing one example of the object circuit. In this object circuit, the cyclic or semicyclic attribute net is connected with the a 1  and a 2  terminals of the element G 1 , and the acyclic attribute net is connected with the a 3  terminal of the element G 1 . 
     The element G 1  is the logic element. At first Step S 2 _ 2 _ 1 , the element G 1  having two or more input terminals connected with the cyclic and semicyclic attribute nets is recognized and stored in the storage unit  5 . 
     Next, at Step S 2 _ 2 _ 2 , the element G 1  is the multiplexer element so that the routine shifts to Step S 2 _ 2 _ 3 . 
     At Step S 2 _ 2 _ 3 , the clock selecting logic flag is raised for the element G 1 . At Step S 2 _ 2 _ 10 , the routine is ended. 
     On the other hand, FIG. 32 is a circuit diagram showing still another example of the object circuit. In this object circuit: the semicyclic attribute net is connected with the a 1 , a 2 , a 3  and a 4  terminals of the element G 1 ; the acyclic attribute net is connected with the a 1  terminals of the elements G 2 , G 3 , G 4  and G 5 ; the cyclic attribute net is connected with the a 2  terminals of the elements G 2 , G 3 , G 4  and G 5 ; and the signals from the data output terminals of the flip-flops or the latches are connected with the a 1  and a 2  terminals of the elements G 6 , G 7 , G 8  and G 9 . 
     The elements G 1 , G 2 , G 3 , G 4 , G 5 , G 6 , G 7 , G 8  and G 9  are the logic elements. At first Step S 2 _ 2 _ 1 , the element G 1  having an input terminal connected with two or more cyclic and semicyclic attribute nets is recognized and stored in the storage unit  5 . 
     Next, at Step S 2 _ 2 _ 2 , the element G 1  is not the multiplexer element so that the routine shifts to Step S 2 _ 2 _ 4 . 
     At Step S 2 _ 2 _ 4 , the back trace is executed from the a 1 , a 2 , a 3  and a 4  terminals of the element G 1 , and the elements G 2 , G 3 , G 4  and G 5  having input terminals connected with the cyclic and acyclic attribute nets are recognized and stored together with the connection information with the remaining elements in the storage unit  5 . 
     At Step S 2 _ 2 _ 5 , the back traces fails to reach the data output terminals of the flip-flops or the latches so that the routine shifts to Step S 2 _ 2 _ 7 . 
     At Step S 2 _ 2 _ 7 , the back trace is executed from the a 1  terminals of the elements G 2 , G 3 , G 4  and G 5 , and the elements G 6 , G 7 , G 8  and G 9  having input terminals connected with the signals coming from the data output terminals of the flip-flops or the latches to construct input logic functions to the a 1  terminals of the elements G 2 , G 3 , G 4  and G 5  thereby to calculate the logic product and the logic sum and to store the results in the storage unit  5 . In the case of this circuit diagram: the input logic function to the al terminal of the element G 2  is a·b; the input logic function to the a 1  terminal of the element G 3  is a·/b (wherein slash “/” means the logical inversion of the slashed signal); the input logic function to the al terminal of the element G 4  is /a·b; and the input logic function to the a 1  terminal of the element G 5  is /a·/b. 
     The logic product of the outputs of the elements G 2  to G 5  is: 
      ( a·b )·( a·/b )·(/ a·b )·(/ a·/b )=0; 
     and 
     the logic sum is: 
     
       
         ( a·b )+( a·/b )+(/ a·b )+(/ a·/b )=1. 
       
     
     At Step S 2 _ 2 _ 9 , the logic product is 0, and the logic sum is 1. Because of this exclusiveness, the routine shifts to Step S 2 _ 2 _ 3 . 
     At Step S 2 _ 2 _ 3 , the clock selecting logic flag is raised for the elements G 1 , G 2 , G 3 , G 4  and G 5 . At Step S 2 _ 2 _ 10 , the routine is ended. 
     A specific example of the operation by the extraction S 7  of the clock waveform candidates for the acyclic flip-flops and the acyclic latches by taking up another example of the object circuit. FIG. 33 is a circuit diagram showing one example of the object circuit. This object circuit is provided with: external input pins CLK 1 , CLK 2  and CLK 3  to be fed with three kinds of clock signals from the outside; an external input pin DIN to be fed with the data signal from the outside; and an external output pin DOUT for outputting the data signal to the outside. 
     All the elements FF 1 , FF 2 , FF 3  and FF 4  are the flip-flops, and the combination circuit has one having no feedback path therein. On the other hand, the net 1  is an acyclic attribute net. 
     At first Step S 7 _ 1 , the net 1  and the element FF 1  having a cyclic attribute signal to the clock terminal cp and an output terminal connected with the net 1  are recognized and stored in the storage unit  5 . 
     Next, at Step S 7 _ 2 , the element connected with the cp terminal of the element FF 2  is only the FF 1  so that the routine shifts to Step S 7 _ 3 . 
     At Step S 7 _ 3 , with respect to the data output terminal q of the element FF 1 , an inverted virtual clock of the FF 2 , i.e., the inverted clock of a duty of 50% having a cycle twice as long as that of the CLK 1 , as shown in FIG. 34, and an uninverted virtual clock of the FF 2 , that is, the uninverted clock of a duty of 50% having a cycle twice as long as that of the CLK 1  are defined and stored in the storage unit  5 . 
     At Step S 7 _ 5 , the timing chart shown in FIG. 34 is prepared, and it is stored in the storage unit  5  that the use of the inverted virtual clock of the FF 2  for the setup analysis in the data transfer from the FF 3  and the use of the uninverted virtual clock of the FF 2  for the hold analysis are the most strict condition, and that the use of the uninverted virtual clock for the setup analysis in the data transfer to the FF 4  and the use of the inverted virtual clock of the FF 2  for the hold analysis are the most strict condition. At Step S 7 _ 4 , the routine is ended. 
     A specific example of the operation by the asynchronous transfer extraction S 7  by taking up another example of the object circuit. FIG. 35 is a circuit diagram showing one example of the object circuit. This object circuit is provided with: external input pins CLK 1  and CLK 2  to be fed with two kinds of clock signals from the outside; an external input pin SEL to be fed with a clock switching signal from the outside; an external input pin DIN to be fed with the data signal from the outside; and an external output pin DOUT for outputting the data signal to the outside. 
     All the elements FF 1 , FF 2 , FF 3 , FF 4 , FF 5  and FF 6  are the flip-flops, and the elements G 1 , G 2 , G 3  and G 4  are the logic elements, of which the element G 2  has a clock selecting logic element flag raised. on the other hand, the data output terminal q of the FF 1  and the output terminal of the element G 4  are dump points for generating clock waveforms. 
     At first Step S 5 _ 1 , an oriented graph (V 1 , A 1 ) having a set of apexes V 1 ={CLK 1 , FF 1 , G 4 } and a set of sides A 1 ={(CLK 1 , FF 1 ), (FF 1 , G 4 )}, and an oriented graph (V 2 , A 2 ) having a set of apexes V 2 ={CLK 2 , G 4 } and a set of sides A 2 ={(CLK 2 , G 4 )} are constructed and stored in the storage unit- 5 . 
     Next at Step S 5 _ 2 : the set F 1 ={FF 5 , FF 6 } of the flip-flops and the latches using the apexes of the oriented graph (V 1 , A 1 ) as the clock source and the set F 2 ={FF 4 , FF 6 } of the flip-flops and the latches using the apexes of the oriented graph (V 2 , A 2 ) as the clock source are recognized and stored in the storage unit  5 ; a set P={(FF 4 , FF 5 ), (FF 5 , FF 6 )} of pairs transferring data at the elements FF 4 , FF 5  and FF 6  is recognized and stored in the storage unit  5 ; the data transfers (FF 4 , FF 5 ) between the flip-flops and the latches contained in the F 1  and the flip-flops and the latches not using the apexes of the oriented graph (V 1 , A 1 ) as the clock source are recognized as the asynchronous transfers; and the data transfers (FF 4 , FF 5 ) and (FF 5  and FF 6 ) between the flip-flops and the latches contained in the F 2  and the flip-flops and the latches not using the apexes of the oriented graph (V 2 , A 2 ) as the clock source are recognized as the asynchronous transfers. From these results, it is recognized and stored in the storage unit  5  that the data transfers (FF 4 , FF 5 ) are the asynchronous transfers irrespective of the state of the clock selecting logic element G 2 , and that the data transfers (FF 5 , FF 6 ) are the asynchronous transfers only when the oriented graph (V 2 , A 2 ) is selected by the clock selecting logic element G 2 . Then, the routine is ended. 
     Thus, in order to recognize the asynchronous transfer path or the elements constructing this path, the passage of the in-element path from the clock terminal to the data output terminal is admitted, and the elements having admitted the aforementioned passage from the external terminals and the clock path passing through the clock selecting element such as the multiplexer are expressed by the graph jointing the clock sources to grasp the set of the elements using the clock sources of the graph. Moreover, the data transfer between the element using the clock source of an i-th graph as the clock source and the element not using the clock source of the i-th graph as the clock source is recognized as the asynchronous transfer. If the element of the path recognized as the asynchronous transfer is one using the apexes of the graphs different before and after the selecting logic, the path is always the asynchronous transfer. If the element of the path recognized as the asynchronous transfer is one using the apexes of the graphs identical before and after the selecting logic, the path is the asynchronous transfer in accordance with the selected state of the selecting logic. This asynchronous transfer path recognizing method (or the asynchronous transfer path extracting operation) has less data to be processed by the computer than that of the method of grasping the clock path by dividing the clock selecting logic as in the multiplexer. Therefore, the memory capacity necessary for the operations by the computer and for making the table can be reduced to complete the data processing quickly. 
     A specific example of the operation by the extraction S 9  of the multi-cycle path candidates by taking up another example of the object circuit. FIG. 36 is a circuit diagram showing one example of the object circuit. This object circuit is provided with: external input pins CLK 1  and CLK 2  to be fed with two kinds of clock signals from the outside; an external input pin DIN to be fed with the data signal from the outside; and an external output pin DOUT for outputting the data signal to the outside. 
     The element FF 1  is a flip-flop; the element G 1  is a logic element, for which the gated clock  2  flag is raised; and the net 1  has the acyclic attributes. 
     At first Step S 9 _ 1 , the element G 1  having the gated clock  2  flag raised is taken out and stored in the storage unit  5 . 
     Next, at Step S 9 _ 2 , the cycle of the CLK 1  is set to the T_cycle and stored in the storage unit  5  because the attributes of the net connected with the a 1  terminal of the element G 1  are cyclic. 
     At Step S 9 _ 3 , the back trace is executed because the attributes of the net connected with the a 2  terminal of the element G 1  are acyclic, and the flip-flop FF 1  is recognized to store the storage unit  5  with the attributes of the net connected with the cp terminal of the FF 1 . 
     At Step S 9 _ 4 , the routine shifts to Step S 9 _ 5  because the attributes of the net connected with the cp terminal of the FF 1  are cyclic. 
     At Step S 9 _ 5 , the cycle of the CLK 2  is set to the T_acycle and stored in the storage unit  5 , and the routine shifts to Step S 9 _ 9 . 
     At Step S 9 _ 9 , a relation of 2×T_cycles&gt;T_acycles holds, and the path from the clock terminal cp of the element FF 1  to the input terminal a 2  of the element G 1  is stored as the multi-cycle path candidate in the storage unit  5  to present the information to the user from the output unit  10 . The result having decided whether or not that path is the multi-cycle path is inputted by the user from the delay information input unit  2 . If the user judges that the path is the multi-cycle path, the path is stored as the multi-cycle path together with the number of cycles of the setup and the hold, as instructed by the user from the delay information input unit  2 , in the storage unit  5 . If the user judges that the path is not the multi-cycle path, the path is stored as the single path in the storage unit  5 , and the routine shifts to Step S 9 _ 8 . The routine is ended at Step S 9 _ 8 . 
     The static-dynamic timing analysis method thus far described is executed by the computer executing the program. This static-dynamic timing analysis program is the machine program (object program) which is made by compiling the content processed by the static-dynamic timing analysis method on the basis of the source program described in a high-level language such as the C-language and by transforming the compiled program into the object code intrinsic to the target computer. 
     This static-dynamic timing analysis program is so stored in a recording medium such as the magnetic tape, the floppy disk, the hard disk, the CD-ROM or the MO (Magnet-Optical Disk), although not especially limitative thereto, as can be read by the computer. 
     FIG. 40 shows one example of the computer for reading and executing the static-dynamic timing analysis program from the recording medium. 
     A computer  100 , as shown, is exemplified by an engineering work station or a personal computer and is constructed by connecting peripheral devices, as represented by a display  102 , a keyboard  103  and a disk drive  104 , with a body  101  having mounted thereon a processor board packaging a processor and a memory and a variety of interface boards. 
     The aforementioned static-dynamic timing analysis program is stored in a storage medium  105 . This storage medium  105  is mounted on the aforementioned disk drive  104 , although not especially limitative thereto, and the static-dynamic timing analysis program stored therein is read in the body  101  of the computer. For example, the read static-dynamic timing analysis program is loaded in the memory of the computer body  101  and is sequentially decoded to perform the aforementioned static-dynamic timing analyses. On the other hand, the static-dynamic timing analysis program thus read from the storage medium may be installed in the magnetic storage medium of the hard disk device attached to the computer body  101  and may be loaded in the memory and executed at any time. In this case, the static-dynamic timing analysis program may be stored in a data-compressed state in the storage medium  105  so that it may be decompressed when it is installed in the aforementioned hard disk. In these cases or the like, the computer-readable storage medium storing the static-dynamic timing analysis program may be exemplified by any of the magnetic recording media such as the aforementioned storage medium  105 , which is stored with the static-dynamic timing analysis program in the executable state or in the data-compressed state, or the hard disk device packaged in the computer body  101 . 
     Although our invention has been specifically described on the basis of its embodiments, it should not be limited thereto but can naturally modified in various modes without departing from the gist thereof. 
     The effects to be obtained from a representative of the invention disclosed herein will be briefly described in the following. 
     With the clock information recognition unit, more specifically, the information of the clock generated inside can be automatically recognized from the information of the clock information to the external input pin to be fed with the clock signal, from the information of the external input pin to be fed with the set or reset signal, and from the information of the flip-flop or latch element to be diverted for the synchronous/asynchronous set/reset or synchronous/asynchronous load of the counter in the object circuit. 
     As a result, the circuits that are asynchronous with the object circuit and those which are asynchronous with the object circuit can be easily distinguished. 
     Since the asynchronous transfer path (the circuit portion constructing the path) requiring no timing analysis is recognized, the data transfer path through the flip-flops and the latches fed with the acyclic signal in the object circuit as the clock and the data transfer path between the flip-flops and the latches fed with each asynchron ous signal, that is the signal, for which the phase difference between the signals when the power is ON cannot be defined, as the clock can be recognized as separate asynchronous transfer paths. 
     The setup/hold analysis can be executed on the gated clock circuit (clock gate) in the object circuit. 
     Since the multi-cycle path of the input signal having no clock attribute to the logic elements constructing the gated clock circuit is recognized, it is possible to execute the setup/hold analysis of the gated clock circuit by the static timing analysis excluding the pseudo errors in advance. 
     In the recognition of the data transfer path between the flip-flops and the latches, it is possible to analyze in advance the combination of the clocks to be fed to the flip-flops or the latches at the two ends of the aforementioned data transfer path. 
     For the flip-flops and the latches fed with the signals other than the clocks at their clock terminals, the virtual clock is decided on its definability and is set, so that the static timing analysis can also be applied to the asynchronous circuit. In other words, the asynchronous circuit is divided into the cyclic circuit and the acyclic circuit so that the static timing analysis can be made on the cyclic circuit. As a result, it is possible to expect a drastic reduction in the number of analyzing steps. 
     The static timing analysis applying circuit portion and the dynamic timing analysis applying circuit portion can be discriminated to recognize the circuit portion requiring the hazard analysis at the synchronous circuit portion and to execute the dynamic timing analysis to that circuit portion. 
     By causing the dynamic timing analysis applying circuit portion to cover the appearance of the flip-flops along the transmission path of the signals, the dynamic timing analysis of the dynamic timing analysis applying circuit portion can be executed without considering the signal delay time on the data transfer path to the dynamic timing analysis applying circuit portion from the static timing analysis applying circuit portion. 
     The correspondence between the dynamic timing analysis applying circuit portion and the logic hierarchy in the object circuit is discriminated so that the logic hierarchy to execute the dynamic timing analysis can be recognized. As a result, the dynamic timing analysis can be executed by using the input signal information to each logic hierarchy prepared at the logic analysis, thereby to make it possible to expect a reduction in the number of analyzing steps. 
     Along the transmission path of the signals from the flip-flops, as the closest to the input terminals and the output terminals of the static timing analysis applying circuit portion, in the aforementioned dynamic timing analysis applying circuit portion, the flip-flops and the latches outside of the dynamic timing analysis applying circuit portion are discriminated to adjust the propagation delay of the clock signals to the discriminated flip-flops and latches such that the dynamic timing analysis can be made merely by giving only the propagation delay of the clock signals to the aforementioned dynamic timing analysis applying circuit portion and to the flip-flops and the latches in the dynamic timing analysis applying circuit portion at the time of feeding the object circuit with the delay information. As a result, by feeding only the dynamic timing analysis applying circuit portion with the delay information, the dynamic timing analysis of the entire object circuit can be executed, and the input signal information of the entire object circuit, as prepared at the logic analyzing time, can be diverted. This makes it possible to expect the reductions in the time periods and the steps for the analyses.