Paper by D.L Parnas And D.P.Siewiorek Prepared by Xi Chen May 16,2003

1. Readings in Computer Science: Software EngineeringUse of the Concept of Transparency in the Design of Hierarchically Structured Systems Paper by D.L Parnas And D.P.Siewiorek Prepared by Xi Chen May 16,2003

2. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems The overview of the presentation: • Top Down Design / Bottom Up Design • Transparency in Bottom Up Design • Examples of Transparency • Hierarchical test generation

3. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems Terminologies: When you build up the system hierarchy, you create structural levels • Base Machine • the lower level of a hierarchy, maybe hardware or an intermediate software level • Virtual Machine • a level above the base machine • typically implemented in software on the “top” of “ real” hardware platform and operating system. • it hides the complexity of the base machine to make interaction with the system easier

4. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems • When constructing hierarchical systems, each level in such a system provides a virtual machine which hides some aspects of the machine below it. Thus, in designing such a system, we repeatedly face this question: “How do I know the instruction set provides by this machine is suited for the programs which users want to run upon it?”

5. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems • The purpose of this paper: introduce a concept which appears to be useful in the design of hierarchically structured systems The purpose of this paper is to introduce a concept which appears to be useful in the design of hierarchically structured systems.

6. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems Several papers suggest that the solution to software design problems lies in: • beginning with a precise description of the desired system • deriving the internal structure from it the advantages of this solution: • prevent design decisions which remove necessary capabilities • eliminate the risk of constructing a system with unexpected undesirable properties.

7. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems The overview of the presentation: • Top Down Design / Bottom Up Design • Transparency in Bottom Up Design • Examples of Transparency • Discussion • Reference

8. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems • Top Down Design (Also called “Outside In” Design) • one software design technique • Describes and creates a system from the highest • hierarchical level where the full specifications of a • design must be known • Solve a large problem by breaking down the • problem into a smaller problem • Continue until further decomposition can no longer • be achieved

9. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems Problems with Top Down design: • Difficult to obtain full specification • The derivation of a design from such a specification is often not feasible • Can result in software that is unnecessarily inflexible • Can specify unrealistic internal structures • Portions of internal structure could already be fixed For these reasons, pure Top Down is rarely used

10. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems Bottom Up Design • Create the system from a set of lower level • components • Work upwards, solving entire project • Reuse components from other projects • More practical to implement internal structures • first, creating separate modules and joining them • together • Bottom Up is more flexible.

11. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems The overview of the presentation: • Top Down Design / Bottom Up Design • Transparency in Bottom Up Design • Examples of Transparency • Hierarchical test generation

12. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems • Transparency: describes the implementation completeness of the virtual machine with respect to the base machine’s functionality • Complete transparency: the virtual machine has ALL of the functionality of the base machine • Loss of transparency: a lack of functionality with respect to the base machine exists in the virtual machine

13. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems The overview of the presentation: • Top Down Design / Bottom Up Design • Transparency in Bottom Up Design • Examples of Transparency • Hierarchical test generation

14. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems • Preliminary example: The following example is intended to illustrate the concept of transparency

15. Figure 1 shows a diagram of a low level portion of a four wheeled vehicle. Note that each front wheel is connected to two strings a driver controls the steering by pulling on a total of four strings. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems

16. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems • Figure 2 shows the addition of a higher level mechanism based on the mechanism of Figure 1 to provide a more convenient virtual machine for the driver. • The ropes have been wrapped around a steering wheel and attached so that now the vehicle can be controlled by the more easily learned mechanism of turning the wheel in the desired direction. • If this is properly done, it is a very good abstraction from the real machine

17. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems Figure 3 shows some of the possible states of Fig.1

18. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems Figure 3 shows some of the states which were possible with the lower level control mechanism • Positions (a) and (b) will be possible by the use of any reasonably designed steering wheel implementation. • Positions (c) and (d) will no longer be possible with reasonable implementation. • Very sharp turns (e) could be eliminated by some designs and permitted by others.

19. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems • If fig2 is transparency, the states are all accepted. • If fig2 is loss of transparency, the states c, d can’t happen.

20. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems The overview of the presentation: • Top Down Design / Bottom Up Design • Transparency in Bottom Up Design • Examples of Transparency • Hierarchical test generation

21. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems Test generation: The development of hardware/software techniques has brought lots of testing problems. Test development cost and testing cost have become an important portion of the total products costs. Test generation is studied for the particular problem. Test generation and testability analysis in a hardware/software co-design environment

22. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems hierarchical test generation: • test is locally generated for each module • Local design subsequently translated into global design Hierarchical Test Generation Framework:

23. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems Hierarchical test methodologies handle large systems in a divide-and-conquer fashion. • These techniques offer lower test generation costs • Increased test reuse. key idea in these methods is identify control sequences that allow test data to be transparently flow through modules.

24. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems • M has one 4-bit input port X and one 2-bit output port Z. Fig6 Combinational module M

25. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems Transparency of modules can be trivially achieved by providing a direct path from each module input to output with the help of multiplexers. Transparency can be achieved by embedding multiplexers in the behavioral models described using a hardware description language.

26. input T is used to switch M from the normal mode (T = 0) to a pass-through, transparent mode (T = 1). An additional 2-bit output port Y is added to ensure complete transparency of M.

27. Transparency properties: Using this Module, testability requirements at the inputs of a module are translated to equivalent requirements at the output of the module and vice versa.

28. Repeat this transparency concept, we get the hierarchical test generation framework

29. Use of the Concept of Transparency in the Design of Hierarchically Structured Systems • References: 1.PROPERTY-BASED TESTABILITY ANALYSIS FOR HIERARCHICAL RTL DESIGNS http://www.cs.ucsd.edu/groups/rssl/Papers/YIORGOS/icecs_yiorgos99.pdf 2. Synthesis of Transparent Circuits for Hierarchical and System-on-a-Chip Test1 http://www.ee.duke.edu/~krish/ICVD.pdf