JP2007133517A - Method and device for designing semiconductor integrated circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To verify whether or not a part which should not be replaced is changed and to avoid being determined that a latch circuit, etc., not relating to logic is inconsistency in a re-order process when verifying a logical equivalence property of a net list after re-ordering in logical designing of a semiconductor integrated circuit. <P>SOLUTION: A method for designing a semiconductor integrated circuit disposes a cutoff point at a specific point on a connection point of a flip-flop circuit constituting a scan chain after re-ordering, and prevents performing inconsistency determination by rejecting the cutoff point from verification targets when verifying the logical equivalence property. Further, the method makes it possible to verify the fact of no change in the flip-flop circuit prohibited from being re-ordered by setting so as not to set up a specific point at a connecting point of a flip-flop circuit the part of which is prohibited from being replaced through the re-order process. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a design method and design apparatus including a process of verifying logical equivalence of two netlists before and after reordering a scan chain in designing a semiconductor integrated circuit.

  A semiconductor integrated circuit design apparatus designs a logic circuit for realizing a target design specification, generates a logic list for generating a netlist, and generates a test circuit for verifying the logic circuit based on the netlist. Test synthesis means for performing layout and layout reordering means for reordering the layout of the test circuit are provided. Furthermore, it has verification means for verifying the reordered netlist. The present invention relates to the verification means included in the design apparatus.

  The procedure of the semiconductor integrated circuit design process will be described with reference to FIG. First, in step S1, an intended design specification is input to the logic synthesis means, and logic synthesis is performed to generate a netlist NET1 and hold it in the storage device.

  Next, in step S2, the test synthesis means generates a test circuit and a test program by inputting the netlist NET1, and further performs a layout to generate a netlist NET2 including logic circuit arrangement and wiring information. At this time, a scan chain for the scan test is generated.

  The scan test is generally used as one of test methods in a semiconductor integrated circuit that is increasing in scale. That is, when the test mode is set, a scan FF circuit having a scan function is configured using a plurality of flip-flop circuits (hereinafter referred to as FF circuits) arranged in the logic circuit. Connected in a chain to form a scan chain. Then, the input value for the test is given from the scan-in terminal to the input terminal of the combinational logic circuit specified via the scan chain, and the output value obtained by processing the combinational logic circuit is passed again through the scan chain. And output from the scan-out terminal. By comparing the output value with the expected value of the combinational logic circuit, each combinational logic circuit can be independently verified.

A scan chain showing a scan chain generated after test synthesis in FIG. 8 is composed of a scan FF circuit 10, and each input terminal SI and output terminal SO are connected in series in a chain shape.

  The mode setting circuit 20 receives test control signals TRST, TDI, TMS, TCK, etc., and outputs a system mode signal SM to control the scan FF circuit. The system mode signal SM is “0” in the system mode and “1” in the test mode.

  FIG. 9 shows an example of the circuit configuration of the scan FF circuit 10. The scan FF circuit 10 includes a DFF circuit 11, a selector 12, and a NAND gate 13. The selector 12 selects either the input terminal D or the scan-in signal SI according to the signal of the system mode signal SM and connects it to the input terminal I of the DFF circuit 11. The output O of the DFF circuit 12 is input to the NAND gate 13 and is output from the scan-out terminal SO when the system mode signal SM is “1”. A system clock is supplied to the clock input terminal CKL.

  Since the system mode signal SM is set to “0” in the system mode, the input signal applied to the input terminal D is applied to the input terminal I of the DFF 11 and the signal of the output terminal O is output from the output terminal Q. . In this manner, the scan FF circuit 10 can perform the operation of the system targeted by the integrated circuit.

  In the scan mode, the system mode signal SM is set to “1”, and the signal given to the scan-in terminal SI is selected by the selector 12 and applied to the input terminal I of the DFF. The output signal O of the DFF 11 is output from the scan-out terminal SO via the NAND circuit 13.

  In the test synthesis, since the scan FF circuit is selected with reference to a logical connection, the layout of the scan FF circuit after layout is not necessarily close to the target logic circuit. If it is in a distant position, the wiring for connection becomes longer, the area of the wiring area increases, and the delay time due to the wiring becomes longer. Therefore, reordering is performed in which the scan FF circuit in the scan chain formed after the test circuit synthesis is replaced and rewiring is performed.

  In step S3 of FIG. 7, the reordering unit replaces the scan FF circuit, and rearrangement and rewiring are performed accordingly, and a netlist NET3 is generated.

  FIG. 10 shows how the scan FF circuit replacement is executed by reordering. In this example, the scan FF circuit 10 arranged in the order of SFF-A-B-C-D is changed to SFF-B-C-A-D as a result of reordering. However, this change only replaces the FF circuit constituting the scan chain used in the test mode. When the system mode signal SM is “0”, the FF circuit is not reordered. Must remain connected

  As described above, in the reorder process, the scan FF circuit 10 is replaced and the wiring is changed due to the replacement. Therefore, it is necessary to verify whether the system operates correctly even after the change. Furthermore, it must be verified that the test circuit operates correctly in the test mode.

  Although the logic verification of the netlist after reordering can be performed using a logic simulator, the time required for verification increases as the design scale increases, leading to longer design processes and higher costs. It is. Therefore, the logical equivalence verification method that has been developed in recent years has been used. Logical equivalence verification is a method in which a logic circuit is expressed by an expression, and when the expressions of two logic circuits are compared and verified to be equivalent, it can be verified very quickly. There is a feature.

  Step S4 in FIG. 7 shows a procedure for making settings for performing logical equivalence verification. In step S5, the logical equivalence of the netlist NET2 before reordering and the netlist NET3 after reordering is verified based on this setting.

  Next, logical equivalence verification will be described. In order to perform logical equivalence verification, first, a logical circuit constituting a semiconductor integrated circuit is expressed by an expression. For this purpose, the integrated circuit is divided using a circuit group that determines the value of the starting point from the input or output point of the logic circuit constituting the integrated circuit as a logic cone, and each logic cone is expressed by an expression.

  A verification method based on logical equivalence verification will be described with reference to FIG. FIG. 11A shows the logic circuit including the scan FF circuit in the netlist NET2 after the test synthesis. The circuit of the scan FF circuit 10 receives the signal input Ain, the system mode signal SM, and the output signals of the logic circuits B and C, and outputs an output Q. As described above, the circuit shown in FIG. 11A forms a logic cone having the output terminal Q. Here, it is assumed that the logic circuit 17 is a scan FF circuit C.

When the output Qa of the logic cone configured by the circuit of FIG.
Qa = X (Ain, B, C, CLK, SM) (1)
It can be expressed as. When logical equivalence verification is performed, all logical cones are expressed by expressions in this way, and comparison is performed for all expressions of two circuits to be verified. If there is no change in the logic of the integrated circuit due to reordering, the two match completely. If incorrect placement or wiring is performed, the expression at that location will be inconsistent and an error can be displayed and notified. In this way, by comparing the expressions, the logic equivalence of the two netlists can be verified, so that high-speed verification can be performed.

Incidentally, FIG. 11B shows the part (a) in the netlist NET3 after reordering, but the scan FF circuit C is replaced with D in the logic circuit 17 by the reordering. If the operations of the scan FF circuits C and D are the same, the operation is the same regardless of the connection in terms of the operation of the scan chain. However, the output signal Qb of the circuit of FIG.
Qb = X (Ain, B, D, CLK, SM) (2)
It is represented by

  In the logic equivalence verification, the logic equivalence of Qa and Qb is compared. In the system mode, the system mode signal SM is “0”. At this time, since the FF circuits C and D are not logically connected, it is determined that they match.

  However, in the test mode, the system mode signal SM is “1”, and the scan FF circuits C and D are logically connected. Therefore, the expressions (1) and (2) are different and are determined to be inconsistent. When the scan FF circuit is replaced by reordering in this way, all errors are displayed in the logical equivalence verification. Therefore, if logical equivalence verification is performed with the obtained netlist as it is, a large number of errors will be displayed, and misplaced and miswired areas that should be detected will be buried, and the location of the error will be determined. Will become difficult.

Therefore, conventionally, in order to avoid the occurrence of such a large number of error indications, when performing logical equivalence verification, only the verification in the system mode operation is set and the verification in the test mode is omitted. It was. Accordingly, whether or not the test circuit operates normally cannot be confirmed until the semiconductor integrated circuit is actually created and the test is executed.
JP 2004-78759 A Japanese Patent Laid-Open No. 11-73448

  Therefore, a method has been devised for performing verification even in the test mode. When performing the logical equivalence verification in the test mode, if the scan FF circuit is set not to be verified, it is possible to prevent an extra error display.

  The first method is a method of directly setting the system mode value “0” to the system mode signal SM input terminal input to the scan FF circuit in the test mode. In this way, even when the logical equivalence verification is performed in the test mode, the scan FF circuit is set in the system mode, so that the connection corresponding to the system mode is performed. For this reason, the replacement of the FF circuit before and after the reorder is not reflected in the equation, so that an error display can be avoided. However, this method cannot verify the logical equivalence from the SM output of the mode setting circuit 20 to the SM input of the scan FF circuit 10.

  The second method is a method in which the system mode value “0” is directly set to the system mode signal SM terminal of the scan FF circuit at the input of the mode setting circuit 20 in the test mode. Also by this method, the same effect as the first method can be obtained. In this case, in addition to the first method, the wiring path from the output terminal of the mode setting circuit 20 to the scan FF circuit 10 can be verified.

  Furthermore, as a third method, the logic equivalence verification is performed by setting the input signal TRST, TDI, TSM, TCK terminal and the like of the mode setting circuit 20 to the condition that the output of the system mode signal SM is “0”. There is a way to verify. Also by this method, the same effect as method 1 can be obtained. In addition, the mode setting circuit 20 can be verified.

  However, in the third method, since the system mode signal SM is fixed to “0”, the output values related to other test items output from the mode setting circuit 20 are also fixed to specific values. The circuit cannot be tested.

  As described above, in any of the first, second, and third methods, in addition to the logical equivalence verification of the scan chain, the verification after the reorder of the circuit accompanying the system mode and test mode setting is sufficiently performed. I can't.

  Furthermore, in the above method, it is difficult to verify the place where the replacement of the scan FF circuit is prohibited in the reorder process. The order in which the FF circuits around the RAM perform the scan test is strictly set. For this reason, if the scan FF circuit is replaced by reordering, there is a possibility that the test may not be correctly executed, and reordering is prohibited. Therefore, after performing the reorder process, it is necessary to verify whether or not the scan FF circuit in which the reorder is prohibited correctly observes the rules. However, neither the first method nor the second method can be confirmed because the scan FF circuit is excluded from the verification target.

Further, in the scan chain reordering process, a latch circuit may be inserted between the scan FF circuits for the purpose of adjusting timing. Even when the latch circuit is inserted in this way, it is determined that there is a mismatch in the logic equivalence verification, and an error is displayed.
As described above, the problems to be solved by the present invention in the logical equivalence verification are as follows.
(1) The logical equivalence verification before and after the reorder process is simply performed on peripheral circuits other than the scan chain in the test mode.
(2) In the reorder process, it is verified whether or not a portion that should not be replaced has been changed.
(3) Avoid latch judgments that are not related to logic being judged as inconsistent.

  The present invention provides a semiconductor integrated circuit design method and design apparatus provided with means for solving the above-mentioned problems.

  According to the first invention, a step of generating a first netlist including a first scan chain, a second netlist including a second scan chain by reordering the first netlist, Generating scan information and verifying the logical equivalence of the first netlist and the second netlist, and performing the logical equivalence verification, the second information based on the scan information A specific point for verifying logical equivalence is provided at a connection point of the flip-flop circuits constituting the scan chain, and the specific point is excluded from the target of logical equivalence verification.

  In this way, by setting a specific point in advance at the connection point of the scan FF circuit and excluding this specific point from the verification target, the scan FF circuit connected to the specific point is replaced by reordering. Even if this is not the case, it is not subject to verification and judgment of inconsistency can be avoided. Accordingly, a large amount of error display unnecessary for the logical equivalence verification does not occur, and it is possible to take countermeasures for the error displayed if there is some error or cause of malfunction in reordering. In this way, it is possible to perform verification on peripheral circuits other than the scan chain. The setting of a specific point can be easily performed automatically by using scan information. In the logical equivalence verification, only an instruction to remove the specific point from the verification target is added. Therefore, the verification work can be easily performed.

  Further, according to the second invention, when the specific point is provided, the specific point is not provided in the flip-flop circuit in which reordering is prohibited based on the scan information.

  In this way, there is no specific point for flip-flop circuits that need to be verified that they have not been accidentally changed during reordering, so logical equivalence verification is performed. Is done. Therefore, in this case, even a scan flip-flop circuit can be verified. Since the range in which verification can be performed is widened, it is possible to further increase the probability of finding misplacement and miswiring.

  Furthermore, according to the third invention, the reordering step includes a step of replacing a latch circuit inserted between flip-flop circuits constituting the second scan chain adjacent to each other with a buffer circuit. It is characterized by.

  When the latch circuit is inserted, the logic equivalence verification determines that the logic is different from that before reordering. However, since the buffer circuit has no logical effect, it is the same as nothing in the logical equivalence verification. Therefore, if the latch circuit inserted by reordering is set to be replaced with a buffer circuit, it is possible to avoid an error display in the logic equivalence verification.

  FIG. 1 shows a procedure for designing a semiconductor integrated circuit using the present invention. The basic procedure is the same as the conventional procedure described above with reference to FIG. Here, the design specification file 30 is a file storing specifications required for the semiconductor integrated circuit. The net list file 31 is a file storing a net list created by each design tool. The scan information file 32 is a file that stores information related to the FF circuits constituting the scan chain. The latch circuit information file 33 is a file that stores information about the latch circuit inserted between the scan FF circuits constituting the scan chain.

  In step S1, logic synthesis is performed according to the design specification 30 to generate a netlist NET1. Next, in step S2, test synthesis and layout are performed with reference to the netlist NET1 to generate a test circuit and a test program including a scan chain, and layout is performed to generate a netlist NET2 (first netlist). . At this time, scan information including the scan chain configuration and connection information is created and stored in the scan information file SCF1.

  In step S3, reordering involving relocation and rewiring of the scan FF circuit is performed using the netlist NET2, and a netlist NET3 (second netlist) is generated. Information about the scan FF circuit replaced by reordering is stored in the netlist NET3. Further, in relation to the reordering, information on the latch circuit inserted between the adjacent scan FF circuits is stored in the latch information file RCF1.

  In step S4, in order to verify the logical equivalence of the netlists NET2 and NET3, the setting described later is performed on the verification device prior to verification. The setting information may be stored in the scan information file SCF2 and the latch information file RCF2.

  In step S5, the logical equivalence between the netlists NET2 and NET3 is verified using a verification device. At this time, verification is performed using the setting conditions set in step S4. Alternatively, the scan information file SCF2 and the latch information file RCF2 may be referred to as setting conditions for verification. When the verification result satisfies the standard, the design is completed.

  Next, the setting performed in step S4 and the specific execution procedure of the logical equivalence verification performed in step S5 will be described with reference to FIG.

  In step S11, the scan FF circuit used in the scan test is extracted with reference to the scan information created in the netlist NET3, the scan-in terminal SI is defined as a specific point, and a cutting point is provided here. When performing logical equivalence verification, a condition is set so that this cut point is excluded from the verification target. By doing so, it is possible to avoid error display due to inconsistency even when the scan FF circuit is replaced by reordering.

  In step S12, a scan FF circuit in which reordering is prohibited is extracted. A cut point is set for the first scan FF circuit in which reordering is prohibited, and no cut point is provided for the second and subsequent scan FF circuits. For this reason, in step S12, the cut points set in step S11 are removed for the second and subsequent scan FF circuits. By setting in this way, it is possible to verify whether or not the scan FF circuit prohibited from reordering has been changed.

  In step S13, the latch circuit set with the reorder is extracted, and the extracted latch circuit is replaced with a buffer circuit.

  After the above setting, the logical equivalence verification of the netlists NET2 and NET3 is performed in step S14. By performing the settings from step S11 to step S13, it becomes possible to avoid error display due to mismatch in the logical equivalence verification that occurs when the scan FF circuit is reordered.

  In the procedure shown in FIG. 2, the cut points are first provided in all the scan FF circuits, and then the cut points of the scan FF circuits that are prohibited by the Riau are removed, but this order is changed. In a scan FF circuit that is prohibited from being reordered, a cut point is provided only in the first FF circuit, and a cut point is not provided in the remaining scan FF circuits, and then a cut point is set in another scan FF circuit. You can change it to.

  Similarly, in the case of the latch circuit, the same effect can be obtained when the logical equivalence verification is performed even if the step S13 for replacing the buffer circuit is performed before the setting of the step S11 or S12.

  Next, the procedure for making the above settings will be described in order. FIG. 3 shows the scan chain after reordering. This figure is basically the same as FIG. 10, and the same name is given to the same object. Among them, SFF-A to SFF-C of the scan FF circuit 10 are reorder targets, but SFF-D to SFF-F are prohibited from being reordered. Accordingly, the scan FF circuits SFF-D to SFF-F are not changed before reordering.

  Further, in FIG. 3, a latch circuit 21 (RC) is newly inserted between SFF-F and SFF-G of the scan FF circuit 10 for adjusting the timing. FIG. 4 shows the result of setting in step S4 in FIG. 1 for the scan chain shown in FIG. FIG. 4 shows a situation where the cut point CP is set to the input SI of the scan FF circuit 10 to be reordered.

  Further, a cutting point is set at SFF-D which is the head of the scan FF circuit 10 where reordering is prohibited. However, no cut point is set in the subsequent scan FF circuit 10. The latch circuit 21 is replaced with a buffer circuit 22. This will be described below in order.

[Example 1]
First, setting of the cutting point will be described with reference to FIG. FIG. 5A shows the scan FF circuits SFF-A and SFF-B cut out as a part of the scan chain. The scan-in terminal SI of the scan FF circuit SFF-B is connected to the scan-out SO of SFF-A. Therefore, when the scan-in terminal SI of the scan FF circuit is expressed as the starting point of the logic cone LC-1, it can be expressed as shown in FIG.

In this case, the scan-out terminal SO of the scan FF circuit SFF-A is connected to the scan-in terminal SI. Therefore, this logic cone has the formula SI = A, SO (3)
It can be expressed as

Here, when the scan FF circuit SFF-A is replaced with SFF-C by reordering, the previous logical cone equation is SI = C, SO (4)
It is represented by In this way, even if the circuit operation is the same, it is determined that it has been changed to a different one in the equation, and it is detected as a mismatched portion and an error is displayed as described above. Therefore, in the present invention, a connection point of the scan FF circuit is defined as a specific point, and a cutting point CP is newly provided here. This cutting point can be expressed as a new logic cone LC-2 inserted as shown in FIG. In FIG. 5C, the logic cone indicating the connection relationship of the scan FF circuit is expressed by the equation SI = CP (5)
CP = A, SO (6)
It can be expressed as. When the scan FF circuit SFF-A is replaced with SFF-C,
SI = CP (7)
CP = C, SO (8)
It can be expressed as.

  Therefore, when the equations (5), (6) and (7), (8) are compared, the difference is the newly introduced cut point CP, and the equation of the logic cone belonging to the scan FF circuit SFF-B. It can be seen that there is no change between (5) and (7). Therefore, if the condition is set so that the cut point CP is excluded from the logical equivalence verification target when the logical equivalence verification is performed, since the verification is not performed on the cut point CP, the mismatch is not determined. , You can avoid displaying an error. The setting of the cutting point CP can be automatically generated by referring to the scan information file SCF1. The setting condition including the cut point generated in this way can be stored in the scan information file SCF2.

  By setting in this way, when performing logical equivalence verification, referring to the scan information file SCF2 and setting conditions so that the cut point is excluded from the verification target, the logic for the test mode is set. Even if the equivalence check is performed, an extra error display is not caused. Therefore, an error displayed in the logical equivalence verification can be considered as an error generated in the reordering process, so that the process of investigating the cause and correcting the error becomes easy.

  As described above, if the logical equivalence verification according to the present invention is performed, verification can be executed even for the test mode. Therefore, the circuit for setting the test mode that could not be verified conventionally and the test mode are set correctly. It is now possible to verify the test circuit relationship such as

[Example 2]
Next, a method for setting a scan FF circuit in which reordering is prohibited will be described. When performing a scan test with a memory circuit or the like, a test pattern is input for the entire memory circuit. In the case of a circuit in which the stored contents such as the disturb test are greatly affected by the timing of the input signal and the operation of the peripheral circuit, the scan FF circuit cannot be replaced by reordering. Therefore, the setting in step S12 in FIG. 2 is for the purpose of verifying that the scan FF circuit is not replaced by the reorder and that the memory test circuit including the test pattern generation circuit is not changed by the reorder. Yes.

  In FIG. 3, the replacement of SFF-D to SFF-F in the scan FF circuit 10 is prohibited. At this time, a condition is set such that the cut point CP is provided only in the first scan FF circuit and no cut point is provided in the second and subsequent SFF circuits for the scan FF circuit to be replaced. In FIG. 4, the cutting point CP is set only at the scan-in terminal SI of the scan FF circuit SFF-D by this setting. In the second and subsequent scan FF circuits SFF-F and SFF-G, the cut point set in step S11 is deleted.

  The reason why the cut point is set only in the first scan FF circuit will be described. Since the scan FF circuit connected to the scan-in terminal SI of the SFF-D corresponding to the first scan FF circuit 10 is a scan FF circuit belonging to a different logic circuit, replacement is permitted by reordering. Therefore, it is necessary to exclude the input of the head scan FF circuit from the target of the logical equivalence verification. The order of the scan FF circuits SFF-E and SFF-F following the scan FF circuit SFF-D in which the reorder is prohibited should not change after the reorder. Therefore, if the cut-off point CP is set not to be provided at the scan-in terminal SI of the scan FF circuits SFF-E and SFF-F, it becomes a verification target of the logical equivalence verification. Therefore, an error can be displayed when a change is made by mistake. The result set in this way is stored in the scan information file SCF2.

  If the logical equivalence verification is performed by setting the cut point CP as a verification target in such a manner, the scan FF circuit in which reordering is prohibited is verified. Therefore, if the SFF circuit is mistakenly replaced or a connection error occurs, a mismatch is detected and an error is displayed.

  As described above, by performing the setting shown in the present embodiment, it is possible to verify the scan circuit around the memory, which could not be detected by the conventional logical equivalence verification method.

[Example 3]
Next, handling of the latch circuit will be described. FIG. 3 shows an example in which a latch circuit 21 denoted by RS is inserted between the scan FF circuits 10 by reordering. In FIG. 4 showing the setting according to the present invention, the latch circuit 21 inserted between the scan FF circuits SFF-F and SFF-G in FIG. 3 is replaced with a buffer circuit 22 denoted as BF. When reordering is performed, the latch circuit 21 is automatically inserted when timing adjustment is required due to a change in the scan chain, or manually inserted at a position determined to be necessary. . Information on the latch circuit is stored in a latch information file RCF1.

Since the latch circuit 2 has a function of holding a logical value, it is a target of logical equivalence verification. Therefore, when the latch circuit is inserted between the scan FF circuits, an error is detected only by setting the cut point CP in the scan FF circuit.
When the latch circuit is inserted, the formula representing the logic cone is
SI = CP (9)
CP = RT (10)
RT = A, SO (11)
It can be expressed as In the operation of the scan chain, since the latch circuit transmits the logic value without changing it, there is no difference in the result in the signal processing. However, when the logic cone is expressed by an expression, it is expressed by Expression (10) and Expression (11). Since the logical equivalence verification compares the equivalence on the formula, even if only the formula (10) representing the cut point CP is excluded from the verification target, an error is displayed because the formula (11) is different from that before the reorder. .

  Therefore, in the present invention, before performing logical equivalence verification, a process of detecting a latch circuit connected between scan chains and replacing it with a buffer circuit is performed. Since the buffer circuit is a circuit that does not perform any processing logically, when it is expressed by an expression, the buffer circuit is processed as having nothing.

Therefore, after replacing the buffer circuit, the expression representing the logic cone is
SI = CP (12)
CP = A, SO (13)
It becomes. Although the expressions (10) and (13) are different, the cut point CP is set to be excluded from the verification target and logical equivalence verification is performed, so that it is not detected as a mismatch, and an error occurs due to the latch circuit. Can be prevented from being displayed.

  Information of the latch circuit inserted between the scan FF circuits by reordering the scan chain is stored in the netlist NET3 with reference to the scan information file SCF1. Alternatively, information on the latch circuit inserted by reordering may be extracted and stored in the latch information file RCF1.

  After performing the setting for the latch circuit inserted in the scan chain in this way, if the logical equivalence verification is executed under the conditions described in the first or second embodiment, the latch circuit is replaced with a buffer. It is possible to avoid displaying an error when verifying the scan chain.

[Example 4]
In the first to third embodiments, the setting work of setting the disconnection point and replacing the latch circuit with the buffer circuit is performed in advance before executing the logical equivalence verification. However, the same effect can be obtained by performing verification while making a determination during execution of logical equivalence verification instead of performing such setting. In this case, the input of the scan FF circuit is expressed by an expression so as to be a logic cone, and it is determined whether or not the FF circuit is used for the scan FF circuit in the middle of the logic equivalence verification, and is excluded from the verification target. This can be realized by building a procedure.

  FIG. 6 shows a procedure for making a determination during execution of logical equivalence verification. In step S21, the setting condition of the system mode setting signal is determined. If the system mode is set, the logical equivalence verification as in the conventional case is performed as it is in step S25. Next, in step S26, it is determined whether or not the verification target is final. If not, the process returns to step S21 to verify the next verification target again.

  If the test mode is set, it is determined in step S22 whether the verification target is a scan FF circuit. In the case of a scan FF circuit, it is determined in step S23 whether the scan FF circuit is prohibited from being reordered. If reordering is not prohibited, it is necessary to exclude the logical equivalence verification target, so step S25 is omitted, and in step S26, it is determined whether the verification target is final.

  If the scan FF circuit prohibits reordering in step S23, it is determined in step S24 whether or not the scan FF circuit in the scan FF circuit in which reordering is prohibited is the head. If it is at the top, there is a possibility that the previous scan FF circuit has been replaced by reordering, so step S25 is omitted and the process proceeds to step S26.

  In step S24, if the order of the scan FF circuits prohibited to be replaced in the reorder to be verified is the second or later of the FF circuits to be prohibited, it is verified whether or not the replacement is erroneously performed in the reorder. There is a need to. Therefore, the process goes to step 25 to perform logical equivalence verification.

  In this way, it is possible to prevent unnecessary errors from occurring by determining whether or not the scan FF circuit is to be verified at the stage of executing verification, and taking the procedure of omitting the execution of verification.

  If the verification target is not a scan FF circuit in step S22, it is determined in step S27 whether it is a latch circuit inserted in the scan chain. If it is in the scan chain, the expression of the latch circuit is replaced with an expression representing the buffer circuit at the time of execution of verification in step S28, and logical equivalence verification is executed in step S25.

  As described above, the present invention can be implemented even if verification is performed while making a determination at each stage of executing logical equivalence verification. In this case, it is not necessary to prepare a setting in advance before performing logical equivalence verification. Instead, an extra step is required when performing verification. If the processing apparatus that performs logical equivalence verification has sufficient capability and the time required for the determination step is not burdened, it is advantageous that the procedure to be set in advance can be omitted. Whichever choice is made, there is no difference in the sense of implementing the present invention.

  By utilizing the present invention, the logic verification of the netlist after the reorder is performed at high speed by performing the logic equivalence verification based on the netlist before the reordering that has already been verified at the time of test synthesis. It becomes possible to carry out simply. Therefore, it is possible to shorten the man-hours and time required for the logic design of the semiconductor integrated circuit.

  By utilizing the present invention, it is possible to perform logical equivalence verification in a test mode that has been difficult to perform sufficiently in the past, and it is possible to verify most of the circuits around the test circuit. Accordingly, it is possible to avoid the inconvenience that the cause of malfunction is found after the semiconductor integrated circuit is manufactured due to an error that is not found in the verification.

  By utilizing the present invention, it becomes possible to detect a case where a flip-flop circuit that is prohibited from being replaced by reorder in the scan chain is erroneously changed by reordering. It is possible to avoid inconvenience that the test cannot be performed due to a reorder error.

  Furthermore, by using the present invention, it is possible to easily remove the latch circuit inserted between the flip-flop circuits of the scan chain from the verification target, thereby avoiding an obstacle to the logical equivalence verification. .

  Thus, the present invention makes it possible to manufacture an inexpensive and highly reliable semiconductor integrated circuit.

It is a figure which shows the procedure of the design of the semiconductor integrated circuit of this invention. It is a figure which shows the procedure of the logic equivalence verification by this invention. It is a scan chain after the reorder which implements this invention. It is a figure which shows the scan chain which implemented the setting of this invention It is a figure explaining the setting of the cutting point by this invention. It is a figure which shows the procedure of the logic equivalence verification by the 4th Example of this invention. It is a figure which shows the procedure of the design of the semiconductor integrated circuit by a prior art. It is a figure which shows the scan chain after the test synthesis | combination by a prior art. It is a figure which shows the structure of a scan flip-flop. It is a figure which shows the scan chain after the reorder by a prior art. It is a figure explaining a logic equivalence verification procedure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Scan FF circuit 11 DFF circuit 12 Selector circuit 13 NABD gate 15, 16, 17 Logic circuit 20 Mode setting circuit 21 Latch circuit 22 Buffer circuit 30 Design specification file 31 Net list file 32 Scan information file 33 Latch information file

Claims (5)

In logic design of semiconductor integrated circuits,
Generating a first netlist including a first scan chain;
Reordering the first netlist to generate a second netlist including a second scan chain; and generating scan information;
Verifying the logical equivalence of the first netlist and the second netlist,
When performing the logical equivalence verification, a specific point for logical equivalence verification is provided at a connection point of the flip-flop circuit constituting the second scan chain based on the scan information, and the specific point is logically A method of logical design of a semiconductor integrated circuit, characterized in that it is excluded from equivalence verification.   2. The method of logical design of a semiconductor integrated circuit according to claim 1, wherein when the specific point is provided, the specific point is not provided in a flip-flop circuit for which reordering is prohibited based on the scan information.   In the reordering step, the second scan chain is configured to replace a latch circuit inserted between adjacent flip-flop circuits with a buffer circuit when performing the logical equivalence verification. 3. The logic design method for a semiconductor integrated circuit according to claim 1, further comprising: Generating a first netlist including a first scan chain;
Reordering the first netlist to generate a second netlist including a second scan chain and scan information;
Verifying logical equivalence verification between the first netlist and the second netlist,
When performing the logical equivalence verification, a specific point for logical equivalence verification is provided at a connection point of the flip-flop circuit constituting the second scan chain based on the scan information, and the specific point is logically A method for verifying a logic circuit, which is excluded from equivalence verification targets. Test synthesis means for generating a first netlist comprising a first scan chain;
A second netlist comprising a second scan chain by reordering the first scan chain, reorder means for generating scan information;
Logical equivalence verification means for performing logical equivalence verification between the first netlist and the second netlist;
The logical equivalence verifying means performs logical equivalence verification by excluding a specific point of the flip-flop circuit constituting the second scan chain from a verification target based on scan information. Design equipment.

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