1 Case Study Automatic Test System for JPEG Encoder Decoder Cards Pair Lecture - 4

2 References Chapter 3: A-7E: A Case Study in Utilising Architectural Structures from Software Architectures in Practice. Parish D.J. & Bashir O. (1998). Automated Test System for JPEG Video Encoder – Decoder Card Pairs. IEE Computing & Control Engineering Journal. 9(3). Pages 127 – 132. June Available at

3 Objectives A PC-based test station to functionally test JPEG encoder decoder card pairs. Typical equipment operation –Test program reads a test image from the disk. –Test image is loaded into the frame buffer of a frame grabber card. –Encoder compresses the test image and the decoder decompresses the compressed test image. –Frame grabber reads the reconstructed image from the decoder. –Original stimulus test image is compared with the reconstructed response image to determine the quality of the response image.

4 Equipment Configuration

5 Architectural Structures used in the Development of the Test System Module Structure Uses Structure Data Flow Structure

6 Module Structure Modules are division of work into work assignments. Modules designed using the information hiding principle –System details encapsulated in different modules. –Interface of a module reveals aspects of the system used to interface modules with each other. A module guide defines the responsibilities of each module by stating the design decisions. A module may consist of sub-modules.

7 Module Structure (Contd.) Specific goals of module decomposition –Simple module structure. –High cohesion. –Simple interfaces offering low coupling. –Implementation of one module should be change- able without affecting the behaviour of other modules. –Changes in design and implementation of modules should not affect, as much as possible, the interfaces of modules. –Changes in modules not affecting the module interfaces will allow integration and testing of new modules without affecting the remaining system.

8 Modules of JPEG Test System Main Application Module –Contains application-level procedures that implement the test functionality. Image Communicator –Contains modules to Communicate image data to the frame grabber card Initialise the frame grabber Command frame grabber to play or capture image Codec Interface Module –Contains modules to initialise JPEG encoders and decoders via RS-232 links.

9 Modules of JPEG Test System (Contd.) Numerical Processor Module –Contains modules that perform numerical operation on images. –Numerical operations performed include RMS Error Analysis Block Level Error Analysis Pixel Shift Analysis and Jitter Determination User Interface Module –Contains modules to Structure results for display and printing. Develop user interfaces based on menu and form fill-in interaction mechanisms.

10 Modular Decomposition Image Communicator Stimulus Writer Stimulus Reader Frame Grabber Numerical Processor RMS Error Analyser Pixel Shift Analyser Image Block Analyser Pixel Shift and Jitter Analyser User Interface Results Presenter Menu and Forms Generator Main Application System Initialiser Application User Interface Module Diagnostic Initiator

11 Uses Structure Module structure contains no information about the runtime execution of software. Module structure does not contain information as to how two procedures in different modules interact. Procedure A uses procedure B if a correctly functioning procedure B is present. Units of uses structure are procedures. Usage restrictions between procedures of two modules are considered to be shared by all procedures of these modules.

12 Uses Structure (Contd.) Modules in a uses structure may be related through allowed-to-use relationship. Uses structure is conceptually documented with a binary matrix. –Rows and columns each list every procedure in the system. –If element (m,n) is true procedure m is allowed to use procedure n. Difference between calls and uses structures –A procedure A need not call another procedure B to be able to use the results generated by procedure B. –A procedure A can call another procedure B and not use the results generated by procedure B.

13 Uses Structure (Contd.) A system is partitioned into layers. A procedure at a particular level is allowed to use a procedure at the same or different levels. Uses structure describes the manner in which modules interact with each other at runtime to accomplish tasks. Uses structure provides implementers information about the interfaces required.

14 Uses Structure for the JPEG Codec Test System Main Application Image Communicator Codec Interface Numerical Processor User Interface

15 Uses Structure for the JPEG Codec Test System (Contd.) No procedure in any module is allowed to use any procedure in the main application. Procedures in all modules use procedures in the user interface modules via UI callbacks. Procedures in remaining modules are used only by procedures in the main application.

16 Data Flow Structures Units of data flow structures are programs or modules. Links between units represent may-send-to relationship. Links are labeled with the name of the data exchanged between the units. Data flow structures essentially describe the initial coarse grained specification of data and information produced and consumed by the system and its modules.

17 Data Flow Structure of JPEG Codec Test System Main Application Image Communicator Codec Interface Numerical Processor User Interface Image Data To/From Disk Image Data To/From Frame Grabber Prompts and Messages User Commands Commands to Codec Codec Status Image Data Processing Results Progress Messages To/From Codec