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I I I I I I I 1.3 The first two tasks had to be present in every cycle bei.ng pe]~formed at 10 Hz while the other two had to be segmented to fit in the remclining time of the 0.1 second interval. The graphics program was heavily segmented because of the time requirements and the slowness of the plotter. The plotter output consisted of two portions (Figure 1.1.). Qrle was a rectangular grid in longitude and latitude to accommodate the aircl:aft position, the other was a time se:l;ies plot of the pressur8;-a1.t,itudE~ Oem) and SF6 concentrations (signal times 3.33 Volts). The symbols, A, B, C, etc., on the aircraft track correspond to those on the time sieries pattern being marked at the same moments. They a:re four minutes apaJ::'t. A wrap-around feature was set-up for the data. WheneveJ::' the pressure altitude varied by more than 1 km the ordinate was reset to .'0. and the integer part of the altitude marked (similarly for SF6). The fract;ion can be read directly on the ordinate (scale f:rom 0-1). I I I I The graphics program can easily gene:rate plots faster than thE~ plotter can handle them. If the plotter output buffer is full the pJ::'ogram does not send any plotter commands. Instead, it buffers its own data and g:f.ves con- trol to the next task. The graphics prog:ram is the last task: to rE~ceive control and must limit its computations tlO the remainder of the 0.1 second time interval. A time lapse variable was set in memory by the iSB<= 88/40 secondary processor to count milliseconds and to ensure that the elapsed time fits within the 0.1 second time interval. The graphics progrc~ sets the highest priority to obtaining data and buffering them, then plc)tting track, pressure altitude and SF6. The 101i11est priority is giv'en to drawing data labels and such in the plot. I I I I I I I I Another important feature is handling the plotter failure. In such a case the plotter paper is advanced and the plot is restarted. . Additional decisions such as changing page, changing pens or restarting the plotter can be made by manually typing special col:mnands on the CRT. In 1986 a second processor system wa:s built. It has a siix Mbyte Win- chester disk and iSBC 86/l2A and iSBC 88/40 computer boards. The c)riginal system will still service the inertial system, while the second onE~ is designed to handle the FSSP and meteorological data. The IMU data is transmitted frOIll one microprocessor to a.nothel: by means of optical data cable. The data collectilon program receives the DIU and FSSP data, processes them and writes on a magnetic tape (a ta,pe drive was configured in the second system). It also displays data on the CR~~ every 10 seconds. Because of the need to accep't IMU data every 0.1. seconds, the task segmentation had to be done here alslo. Work is in progl'ess tC) add new instruments to the system, including a Ro:semount temperature sensor., a J-W liquid water hot wire and several pressurle sensors to eval uat:e wind direc- tion and speed.