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Embedded Systems November 2000 Vol13_12

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The world of embedded systems is commonly the world of on-the-fly processing, and so it is with our goal-seeking robot. ... in terpenetrating atomic oscillators immersed in a stro ng electric field . The e lectric fi eld caused otherwise undetectabl e random disc ha rges that occasionally upset the oscilla- tors. I was trying to measure the fre- quency ra tio of the two, but th e mean of my measurements was so noisy as to be unusable. Fortunately (since this was my thesis expe ri- ment) , the median of tha t same data took those upsets in strid e. Median filters The world of embedded systems is commonly the world of on-the-fly pro- cessing, and so it is with our goal-seek- ing robot. The data comes in at regu- lar intervals and we must produce a stream of median values. We need a median fil ter. This is a filter that runs in hard real time. We don 't care as much abou t the typical computation time needed to produce the n ext median value as we do about the worst-case time. One goal for our implementation, then, will be to min- imize the worst case computa tion effort. • rl ~I Datpoint i j I ~ Small 1:- Null Z---- ------- I Stopper ----] 1 102 NOVEMBER 2000 Embedded Systems Programming u.--:J- -- Big '::..._:__ ___ .: Buffer --==:;] i ___ n 'I II 'I I ! il l' I ! 'I Scan II q :: II !I Datpoint I ----------:ll l . ' . ----4. I 0 Median Big

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