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 16-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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