WMOD00402

• Project Name: Sierra Cooperative Pilot Project
• Title: Sierra Cooperative Pilot Project - Final Report for Period November 1984 - September 1986
• Date: 6/1/1987
• Weather Modification - Doc Type: Report

1.2

When the inertial platform software and the interfaces between the
computer and the pressure transducer, plotter and the SF6 analyzer were
completed they were then installed in the aircraft. The equipment began
operation with a flight on 25 March 1985. All the devices operated and we
were able to detect SF6. Various software changes were then added to the
computer to make the graphical output clearer. The aircraft operated well,
with the expected minor problems.

The data system was driven by an Intel iSBC 86/330A microprocessor with
a 35 Mbyte Winchester disk and an 88/40 secondary computer board. This sys-
tem was interfaced with an inertial platform (or IMU, inertial measurement
unit). The hardware and software were originally an inertial navigation
system developed for the NASA Doppler Lidar project. The IMU data included
. longitude, latitude, heading of the aircraft, pitch, roll and drift angles.
The IMU data were computed by the program GYRO. ~RO is the central part
of the software for the data system. Its primary function is to compute
positions, keep the platform level at all times and to calibrate the plat-
form's performance. The IMU data are then sent to the graphics program to
be plotted. The graphics program also receives data from a pressure tran-
ducer and the SF6 instrument. It then plots data on the Zeta plotter in
a fixed format.

The data transmission from the instruments and Zeta plotter was handled
by a direct memory access controller and it was scheduled by the MANAGER
program. MANAGER takes plotter commands from a specially-modified version
of the Zeta library and sends them to the plotter as the plotter can accom-
moda te them.

The plotter, the pressure transducer and the SF6 instrument are on a
daisy chain connected by optical fiber cable. Each is activated when it
recognizes its number in a transmitted byte.

A heavy demand was placed on the data system because of the need to
service the inertial platform every 0.1 seconds. Consequently, all tasks
had to be squeezed in this narrow time interval and some had to be segmented.
The iRMX86 operating system of the Intel computer had proved to be too slow
to use with the inertial platform. During the operation of the navigation
program iRMX86 was disabled and hand-coded device drivers were used. Thus
the program had to schedule its own operations. Also, some of the plotter
routines had to be rewritten so that they could be interleaved with the
navigation program without affecting its rate of 10 Hz.

The tasks in the 1985 data system were:

1. servicing the platform and getting the IMU data:
2. obtaining data from the instruments:
3. plotting positions and instrument data: and
4 displaying position and instrument data on CRT (terminal
screen) every 10 seconds and printing data every 30 seconds.

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