#11
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Rover brains?
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#13
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Rover brains?
Kevin Willoughby wrote:
In article , says... Somehow, I'm afraid rover "bluescreened" "Bluescreen" is a Microsoft-ism. Note that Microsoft is legally restrained from doing much of anything with Java. Which, as far as I'm concerned, is it's principle redeeming feature! Brett |
#14
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Rover brains?
Kevin Willoughby writes:
[i] It's nice for rebootable web-based systems but can't stand the tought of bloated, buggy code running inside the poor rover. uh, the first MER lander is rebooting frequently, with (as far as I understand these things) no reason to blame the Java Virtual Machine. Java code does not have to be "bloated, buggy code". Virtual machine architectures are a classic way to to create a small, tight program -- consult Knuth for details. See, for example, FORTH --- which uses a =MUCH= simpler virtual machine than JAVA, and can pack an entire operating system / extensible compiler into a mere 8k... "Bloated, buggy code" is more common in non-Java environments, e.g., MS Office running on MS Windows. "Microsoft code is a way of thinking --- or rather, of =NOT= thinking..." -- Gordon D. Pusch perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;' |
#15
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Rover brains?
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#16
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Rover brains?
"Kevin Willoughby" escribió en el mensaje ... In article , says... Uhh...i heard something about extensive use of JAVA. I'm not quite sure of the extent of "extensive", but yes, Java (not all upper-case, please) was one of the many, many tools used on MER. I would be very surprised to know that the rover itself runs Java code. I don't think Java meets the hard real time requirements of the rover software. For instance, you absolutely need to know how much time each task will need to complete, but in Java you can't predict when the garbage collection will run, making the whole system unpredictable. I do now that the OS is VxWorks, which was designed for RT systems and that C was used (at least partially) in the flight software. The Maestro software is written in Java. It is a simplified version of the system the misson planners use to test the commands they will later send to the rover and it is reasonable to asume that the full version is written in Java too. |
#17
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Rover brains?
Gordon D. Pusch wrote:
See, for example, FORTH --- which uses a =MUCH= simpler virtual machine than JAVA, and can pack an entire operating system / extensible compiler into a mere 8k... You can have JVM-s with sizes within the same order of magnitude. A JIT JVM will obviously be larger, but not by *that* much. -- Gordon D. Pusch perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;' -- Sander +++ Out of cheese error +++ |
#18
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Rover brains?
In article ,
says... In article , (Greg) wrote: IMHO it's the code review process as well as the coding environment that can make all the difference. Yep. For the past 25 years, the software industry has repeatedly discovered that having a second set of eyes see a program is the single best way of improving quality. ie managers that have the attitude of "just get it done on time on matter what" are generally managers to avoid. It isn't just the managers. Long ago, I worked in a startup with very good people. Except the managers of the development team. We developers managed to create a good product despite the attitudes of our managers. As for "get it done on time", well, you thought you had deadline pressure? If my code is late, my company's quarterly numbers will suffer, but as long as things are not too bad, we'll get it released next quarter. You clearly misunderstand the VC-dominated commercial software environment. If the VCs liquidate the company after a bad quarter, there is no "next quarter". In contrast, there will be another launch window for Mars within the next couple of years. -- Kevin Willoughby lid Imagine that, a FROG ON-OFF switch, hardly the work for test pilots. -- Mike Collins |
#19
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Rover brains?
Sander Vesik writes:
Gordon D. Pusch wrote: See, for example, FORTH --- which uses a =MUCH= simpler virtual machine than JAVA, and can pack an entire operating system / extensible compiler into a mere 8k... You can have JVM-s with sizes within the same order of magnitude. A JIT JVM will obviously be larger, but not by *that* much. I am talking about an ENTIRE OPERATING SYSTEM, with EXTENSIBLE COMPILER. The "virtual machine" component of FORTH totals only a few tens of bytes. FORTH is utra-lean and ultra-clean. The JVM is built to MILSPEC. -- Gordon D. Pusch perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;' |
#20
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Rover brains?
In article ,
says... "Kevin Willoughby" escribió en el mensaje ... In article , says... Uhh...i heard something about extensive use of JAVA. I'm not quite sure of the extent of "extensive", but yes, Java (not all upper-case, please) was one of the many, many tools used on MER. I would be very surprised to know that the rover itself runs Java code. I hate to admit a mistake, but: I've tried to find my original source for this and have to admit that I may have confused some of the Java- based Earth-based support software (e.g., Collaborative Information Portal -- CIP), with the software on the rover itself. Sorry about that! I don't think Java meets the hard real time requirements of the rover software. For instance, you absolutely need to know how much time each task will need to complete, but in Java you can't predict when the garbage collection will run, making the whole system unpredictable. Even without garbage collection, most modern computers are unpredictable. Modern computers are quite dependent on a cache for good performance. Many systems have multiple levels of cache. How long it takes to perform a task is a non-trivial statistical computation. A lot of research has been done on garbage collection. It is possible to limit the CPU time consumed in garbage collection, allowing a real time system (at the expense of perhaps requiring a bit more memory). This kind of software can get complex. "Simpler is better" is a valid philosophy. Yet I wouldn't assume that Java can't be used in real time systems. Note that the very first Java Specification Request (http://www.jcp.org/aboutJava/communi.../first/jsr001/, http://www.rtj.org/) is for real-time Java. -- Kevin Willoughby lid Imagine that, a FROG ON-OFF switch, hardly the work for test pilots. -- Mike Collins |
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