Fig. Hist-1. Example of a histogram which records the distribution of dice throws.
Design an RT system to implement a histogram recorder. The number of available memory words is 1024 with a word size of 16 bits.
DESIGN CONSIDERATIONS
There are limitations which affect this design. If the number of event types, M, is greater than the number of memory words available, all possible events cannot be uniquely represented. In this case a record can be maintained for only a subset of the original set of events. A possible solution to this problem is to group the events into distinct classes such that the number of classes does not exceed the number of available memory words. A second limitation is that only a finite range of values may be stored in a record, given a word size of W bits. The histogram recorder can correctly maintain only those records with values in the range zero to (2^W)-1. The use of scaling or shorter time periods of observation are possible solutions to this problem.
Finally, it is important that the recorder operate in a short time to minimize the necessary duration of time between two events at ti and ti + /\t. In this way, the event occurrence rate can be high.
The following functions are necessary in the design:
1. Initialization - A switch should be provided which initiates a process to reset each word in memory to zero.
2. Histogram update - This is a process which increments the histogram by one for each event, x(ti).
3. Display - A display process which reads a memory word and displays the value on a T(CRT display) should be incorporated in the design. This process can be used to successively plot each value of M[0:1023]<15:0> as shown in Figure Hist-1. A K(clock) should provide a signal to initiate the display process which should be capable of plotting a new point every 30 microseconds. (This fast plotting time is required so that the 1024 points can be plotted in about 30 milliseconds, providing a flicker rate of about 33 frames/second.)
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