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Rover brains?
As soon as I hear VxWorks I get the impression that they went out and
hired some engineers with C programming experience. These people do not want to know what is really going on so they count on others to write them an operating system and the finger pointing can begin. The people who wrote the software probably have not read the actual code written by the compiler and they have not read or do not understand the real time system. They work in an abstract world of multiprocessing, inter process messaging, semaphors, etc. My experience has shown that I could get a factor of 100 improvement over this above method and I could get absolute reliability - updateability by switching over to assembly language and writing all the code myself. I even wrote my own editor, assembler, development system, operating system etc. Of course this is a labor intensive method not suited for viewgraphs. The ancient art of assembly and machine code programming is dying out and so nobody can make reliable electronic systems anymore. No wonder I keep hearing of yaw dampers crashing airplanes and thrust reversers deploying in flight. Zoltan |
#2
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Rover brains?
Zoltan Szakaly wrote: As soon as I hear VxWorks I get the impression that they went out and hired some engineers with C programming experience. These people do not want to know what is really going on so they count on others to write them an operating system and the finger pointing can begin. The people who wrote the software probably have not read the actual code written by the compiler and they have not read or do not understand the real time system. They work in an abstract world of multiprocessing, inter process messaging, semaphors, etc. My experience has shown that I could get a factor of 100 improvement over this above method and I could get absolute reliability - updateability by switching over to assembly language and writing all the code myself. I even wrote my own editor, assembler, development system, operating system etc. Of course this is a labor intensive method not suited for viewgraphs. The ancient art of assembly and machine code programming is dying out and so nobody can make reliable electronic systems anymore. No wonder I keep hearing of yaw dampers crashing airplanes and thrust reversers deploying in flight. Zoltan JPL switched from roll your own to VxWorks with the Mars Prospector, as the budget didn't support the roll your own, not to mention the nightmare that the typical cyclic executive creates from a maintenance perspective every time you need to change the timing. As far as those yaw dampers you heard about, those airplanes had analog computers on them--at least the yaw damper was analog. Not sure about the thrust reversers. Those airplanes may have had digital engine controllers, which were probably written in Jovial or assembly--with home-grown executives. Realistically, writing with assembly and rolling your own executive is fine for simple systems, but when you start getting to the levels of complexity that require 32 bit hardware, writing your own and using assembler may very well be more error-prone and certainly more costly than using a well developed OS and language, whether commercial or open source. |
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Rover brains?
On Sun, 25 Jan 2004 17:44:48 GMT, John Ahrens
wrote: As far as those yaw dampers you heard about, those airplanes had analog computers on them--at least the yaw damper was analog. The yaw dampers in many aircraft are mechanical or electromechanical, not with analog computers. Not sure about the thrust reversers. Those airplanes may have had digital engine controllers, which were probably written in Jovial or assembly--with home-grown executives. The first production digital engine control system was probably the spike controller retrofit for the SR-71, some time in the '80s. The first digital FADEC/HIDEC/DEEC was flown on the Dryden F-15 about then. Thrust reversers are electromechanical. They don't use analog or digital computers. They also don't use feedback. They're bang-bang systems, so there's no need for proportional control. Mary -- Mary Shafer Retired aerospace research engineer |
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