Abstract:
A microprocessor core  4  is modeled using an obscured model  22  of the core functionality and a non-obscured model  24  of the scan chains that in that particular instance are associated with the microprocessor core  4 . Validation of the design of a scan chain controller  12  can be achieved using the non-obscured scan chain model  24 . Different scan chain models  24  can be relatively easily provided to model different scan chain physical configurations whilst leaving the more difficult to produce obscured core model  22  unaltered.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the validation of integrated circuit designs. More particularly, this invention relates to the validation of integrated circuit designs in which part of the design is obscured to maintain its confidentiality. 
     2. Description of the Prior Art 
     An important part of the development of a new integrated circuit is the validation of the design for that circuit. This typically takes place before any physical examples of the integrated circuit are produced in an effort to remove errors from the design. Sophisticated computer program tools exist to assist in this validation process. 
     A typical design validation process will use models of different portions of an integrated circuit design and with these models test that signals are correctly exchanged and processed by the different elements within the integrated circuit as a whole. It will be appreciated that with the increase in system-on-a-chip designs, an integrated circuit may contain different portions provided by different suppliers. As an example, a single integrated circuit may include a microprocessor core provided by a first supplier, a random access memory provided by a second supplier and a number of peripheral devices provided by a third supplier. The designs of many of these portions represent confidential and valuable property. In order to protect this property, it is known to provide obscured models of portions of integrated circuits that can be used in design validation and yet do not reveal valuable information regarding the internal design of that portion. 
     A problem with obscured models is that it is difficult for someone other than the originator of that model to make any changes to it. This can cause problems as it is desirable that at least some trusted parties other than the originator of the obscured model should be able to slightly alter that model for their own purposes. An example of this is that different users of a microprocessor core represented by an obscure model may wish to provide different sets of scan chains for use in testing that microprocessor core. Whilst one of these scan chains may be a wrapper scan chain provided outside of the microprocessor core, it is likely that further scan chains will be within the interior of the microprocessor core and accordingly will require modification of the obscured model of that microprocessor core if they are to be properly modeled by that obscured model during the validation process. 
     SUMMARY OF THE INVENTION 
     Viewed from one aspect the present invention provides a method of validating an integrated circuit design having a plurality of circuit portions including: 
     (i) a prevalidated circuit portion having an obscured prevalidated circuit portion represented by an obscured prevalidated circuit portion model and a non-obscured prevalidated circuit portion represented by a non-obscured prevalidated circuit portion model, and 
     (ii) an unvalidated circuit portion represented by an unvalidated circuit portion model, said method comprising the steps of: 
     (iii) simulating interaction between said unvalidated circuit portion and said non-obscured prevalidated circuit portion using said unvalidated circuit portion model and said non-obscured prevalidated circuit portion model; and 
     (iv) verifying correct interaction of said unvalidated circuit portion model and said non-obscured prevalidated circuit portion model during said step of simulating interaction between said unvalidated circuit portion and said non-obscured prevalidated circuit portion to validate design of said unvalidated circuit portion in interaction with said non-obscured circuit portion, wherein 
     (v) said unvalidated circuit portion model does not interact with said obscured prevalidated circuit portion model during said step of simulating interaction between said unvalidated circuit portion and said non-obscured prevalidated circuit portion, and said prevalidated circuit portion includes one or more scan chains, said one or more scan chains being part of said non-obscured circuit portion and modeled by said non-obscured prevalidated circuit portion model. 
     The invention recognizes that whilst a prevalidated circuit portion, such as a microprocessor core and its associated scan chains, that is provided on a general basis should preserve the confidentiality of the important information, it is possible to segment the model provided into an obscured part and a non-obscured part. The obscured part can be provided by the originator of the valuable design and the non-obscured part, for example, provided by the originator or by trusted parties to model those portions of the pre-validated circuit portion over which it is desired to give those trusted parties some control. This prevalidated model having obscured and non-obscured portions that is then released to, for example, a system-on-a-chip provider enables validation of the circuits produced by that system-on-a-chip provider to be carried out using a prevalidated model for a portion of that design and maintains the confidentiality of the crucial design information whilst allowing a degree of flexibility in the design of the prevalidated portion without requiring a completely new obscured model to be generated. 
     As a specific example, a microprocessor core design may be represented by an obscured model. This design may be released to trusted parties who customize the design to a form in which it can be manufactured by their particular manufacturing processes and which will have its own set of most appropriate scan chains. When this microprocessor core and associated scan chains are included within a larger system-on-a-chip design, it is important that the complete design including interaction with both the microprocessor core represented by the obscured model and the scan chains associated with the non-obscured model are properly validated. A mistake in the way the system-on-a-chip integrated circuit is produced associated with the operation of the scan chains may be just as difficult and expensive to rectify as one associated with the operation of a microprocessor core. However, providing a non-obscured model of the scan chains allows these to be validated as part of the design without revealing valuable confidential information regarding the interior of the microprocessor core that is represented by the difficult to produce and tightly controlled obscured model. 
     It will be appreciated that whilst the above specific example refers to microprocessor cores and scan chains (both wrapper scan chains and internal scan chains), the invention may also be used for different circuit portions within an integrated circuit design. For example, the logic for a custom functional block (such as a coprocessor) that is added by a trusted party to an existing processor. 
     Viewed from another aspect the present invention also provides a model for a prevalidated portion of an integrated circuit having an obscured prevalidated circuit portion and a non-obscured prevalidated circuit portion, said model comprising: 
     (i) an obscured prevalidated circuit portion model representing said obscured prevalidated circuit portion; and 
     (ii) a non-obscured prevalidated circuit portion model representing said non-obscured prevalidated circuit portion, wherein 
     (iii) said prevalidated circuit portion includes one or more scan chains, said one or more scan chains being part of said non-obscured circuit portion and modeled by said non-obscured prevalidated circuit portion model. 
     Viewed from a further aspect the invention also provides a method of producing a model of a prevalidated portion of an integrated circuit having an obscured prevalidated circuit portion and a non-obscured prevalidated circuit portion, said method comprising the steps of: 
     (i) providing an obscured prevalidated circuit portion model representing said obscured prevalidated circuit portion; 
     (ii) generating a representation of said prevalidated circuit portion including both said obscured prevalidated circuit portion and said non-obscured prevalidated circuit portion; and 
     (iii) using data derived from said step of generating said representation of said prevalidated circuit portion to generate a non-obscured prevalidated circuit portion model representing said non-obscured prevalidated circuit portion; whereby 
     (iv) said obscured prevalidated circuit portion model and said non-obscured prevalidated circuit portion model together represent said prevalidated circuit portion, wherein 
     (v) said representation of said prevalidated circuit portion is a representation of component placement and signal routing for said prevalidated circuit portion, and said non-obscured prevalidated circuit portion comprises one or more scan chains. 
     Further aspects of the invention, including aspects of the invention represented by a computer program product, such as a computer program recorded on a recording medium or transmitted via a network, are also set out in the appended claims. 
     The above, and other objects, features and advantages of this invention will be apparent from the following detailed description of illustrative embodiments which is to be read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically illustrates a system-on-a-chip integrated circuit; 
     FIG. 2 schematically illustrates a model of a microprocessor core including an obscured portion and a non-obscured portion; 
     FIG. 3 schematically illustrates the generation of the test deliverables in the production of a integrated circuit; and 
     FIG. 4 schematically illustrates a general purpose computer of the type which can be used to implement the modeling techniques discussed in relation to FIGS. 1 to  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 schematically illustrates an integrated circuit  2  composed of a microprocessor core  4 , a cache memory  6 , an input/output circuit  8  and a UART circuit  10 . Each of these different components of the integrated circuit  2  has one or more serial scan chains associated with it. These serial scan chains are all controlled by a scan chain controller  12 . 
     The producer of the integrated circuit  2  may acquire the design of the microprocessor core  4  from another party. Accordingly, in the illustrated example, the portion within the box  14  has been provided to the integrated circuit producer who does not know the details of its design. This portion includes both a wrapper scan chain  16  and a plurality of internal scan chains  18 ,  20 . The contents of the box  14  have been prevalidated by their supplier. However, it is important that the interaction between the contents of the box  14  and the scan chain controller  12  should be validated as correct. As an example, a single inappropriate inverter within the scan chain path that is part of the scan chain controller could cause incorrect test results to be produced when those scan chains were used to test the proper manufacture of the integrated circuit  2 . The scan chain controller  12  also controls scan chains associated with the cache memory  6 , the input/output circuit  8  and the UART circuit  10 . 
     FIG. 2 schematically illustrates the model of the prevalidated portion  14  that is provided to the producer of the integrated circuit  2  to validate the integrated circuit  2  as a whole. This model includes an obscured portion  22  and a non-obscured portion  24 . The obscured portion  22  models the microprocessor core with its many complex input and output signals and behavior. The non-obscured model  24  models the scan chains  16 ,  18  and  20  that are added to the microprocessor core  4  to suit the particular circumstances. The obscured model  22  has a defined signal interface via which it communicates with other elements (cells) within the system-on-a-chip integrated circuit  2  to enable validation of that interaction to take place. The non-obscured scan chain model  22  is provided in open RTL (register transfer language) that may be readily produced to suit the particular requirements in an individual case with much less difficulty than would be associated with producing a new obscured model  22  that also modeled the particular scan chains used in that instance. In practice, the verification of the interaction between the scan chain controller  12  and the core  4  can be achieved by testing the interaction between the non-obscured scan chain model  24  and a scan chain controller model  26  that is produced by the integrated circuit producer without needing any interaction with the obscured core model  22 . The interaction between the obscured core model  22  and the non-obscured scan chain model  24  has already been validated by the provider of these elements and accordingly need not be examined when validating the design of the scan chain controller  12  using the scan chain controller model  26 . On a practical level, the interaction between the scan chain controller model  26  and the non-obscured scan chain model  24  can be examined by modeling the scanning in and scanning out of the test vectors for the microprocessor core  4  to check this is correctly performed. In practice the non-obscured scan chain model  24  can be very simple with the function of a scan chain being one that records serially input data, delays it for a predetermined period and then replays that or other data. The correct scanning out of known correct responses to input test vectors can also be verified. 
     FIG. 3 schematically illustrates the process of producing test deliverables for a microprocessor core. The core provider generates an obscured core model  22  as well as a non-obscured core model  28  and scripts  30  for synthesizing a core design using that non-obscured core model  28 . These three items  22 ,  28  and  30  are provided by the core provider to a trusted party who generates a prevalidated microprocessor design and its associated test deliverables. Different such trusted providers may use different manufacturing processes that require different scan chains and test patterns to be used to test for correct manufacture of their design. The process of synthesis  32  using the scripts  30  and the non-obscured core model  28  generates a gate level net list  34  for the microprocessor core. The appropriate scan chains and test patterns for that microprocessor core represented by the net list  34  are then generated by the scan chain insertion and automatic test pattern generation process  36 . The output of this process  36  is a final net list  38  for the microprocessor core that includes both component placement and signal routing information at a level in which it can be used to fabricate the microprocessor core  4 . The process  36  also produces the test vectors  40  for use with the scan chains that have been inserted and a log file  42  giving details of the scan chains that have been inserted. The process  44  then uses a scripting program to read the log file  42  and the test vectors  40  to produce a non-obscured scan chain model  46  of the inserted scan chains, such as in open RTL. 
     The test deliverables representing the prevalidated microprocessor core that are released are the obscured core model  22 , the non-obscured scan chain model  46  and the test vectors  40 . Using these three elements, the producer of the integrated circuit  2  can model the microprocessor core  4  in a manner that allows the design of the integrated circuit  2  as a whole to be validated whilst maintaining the confidentiality of the design of the microprocessor core  4 . It will be appreciated that the obscured core model  22  and the non-obscured core model  46  may be combined into a single model of the core, the top level of which is unobscured and holds together the obscured core model  22  and the non-obscured core model  46 . 
     FIG. 4 schematically illustrates a general purpose computer  48  of the type which can be used to perform the modeling and verification/validation of designs as discussed above. This general purpose computer  48  includes a central processing unit  50 , a random access memory  52 , a hard disk drive  54 , a removable media drive (such as a CD or floppy disk drive)  56 , a display driver  58  and display  60  and a user input/output circuit  62  with an associated keyboard  64  and mouse  66 . 
     The general purpose computer  48  executes computer programs that may be loaded via the removable media drive  56  and stored on the hard disk drive  54 . During execution of these computer programs by the central processing unit  50 , the working memory is provided by the random access memory  52 . User displays indicating the results of the execution of the program are provided by the display driver  58  and the display  60  whilst user inputs to control the operation of the computer program are provided by the user input/output circuit  62  and the keyboard  64  and mouse  66 . The circuit models may also be loaded via the removable media drive  56  and stored upon the hard disk drive  54 . 
     Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope and spirit of the invention as defined by the appended claims.