THE IMPLEMENTATION OF BRL 



The implementation of BRL by means of the second generation Bugsystem 

 differs significantly (both in hardware and in software) from that of the 

 prototype system. This section outlines the main features of the new system, 

 giving reasons for their importance. 



A New Bugwatcher 



The Bugwatcher hardware was redesigned to utilize medium scale 

 integration (MSI) circuitry. Algorithmic state machine (ASM) charts were 

 employed to formulate and to document the new design. Functionally, the 

 new Bugwatcher is similar to its earlier counterpart: it extracts digital X-Y 

 coordinate pairs representing points belonging to image outlines from the video 

 raster scan and stuffs these coordinates into the computer's direct memory 

 access (DMA) channel. The computer program to input these data buffers them 

 and writes them to disk, thereby allowing the collection of extremely long data 

 records. Within such a record each frame of video data is represented as a 

 vector. Each video vector sent by the Bugwatcher to the computer contains not 

 only a variable length list of coordinate data, but also includes a leading header 

 of fixed length. The elements of this header are referred to as "vector 

 attributes" and are employed to encode information associated with each 

 vector. Video data possess four 1 6-bit words of attribute information supplied 

 by the Bugwatcher hardware: (1) a unique word consisting entirely of zeroes 

 used by the software to delimit frame boundaries; (2) a descriptor word which 

 contains an encoding of the frame rate at which the video data were digitized 

 and the on-off status of tone stimulus markers; (3) a total frame counter that 

 can be used to determine relative or absolute time intervals between data 

 segments recorded at varying time intervals; and (4) auxiliary digital input 

 which allows an encoding of an experimental variable (e.g., the direction of the 

 source of stimulation) to be automatically associated with each video frame. 

 Representation of stimulus conditions is discussed in more detail below (see 

 "Coupling to Research Environments"). This division of vectors into attributes 

 and data applies to all vectors manipulated by Bugsystem software. However 

 the meaning of each attribute depends on the type of data; e.g., one of the 

 attributes of a path (represented as a single vector) is the starting frame 

 number. 



The Implementation Language— FORTRAN IV 



The prototype BRL system was implemented entirely in assembler language 

 on an IBM 1800 computer and ran as a stand-alone system with no operating 

 system support. This made it non-portable and difficult to maintain and 

 expand. The new BRL system was to overcome these major shortcomings; 



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