Subject:
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Re: Some comments (long)
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 7 May 1999 16:39:35 GMT
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Original-From:
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Paul Speed <pspeed@augustschellNOSPAM.com>
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Viewed:
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1259 times
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Mark Tarrabain wrote:
>
> "John A. Tamplin" wrote:
>
> > One of the reasons for choosing JVM is the development environments already
> > available for every platform. For debugging, you simply load the classes
> > which emulate the RCX's hardware and everything else is already there.
>
> You have reiterated exactly what I expected would be one of the most popular
> reasons to want to implement a JVM for the RCX.
>
> I hope you don't think I'm against what you're attempting to do... it's just that
> I, like Kekoa, believe that the endeavor you are about to undertake may transcend
> the limits of feasability. There is not a lot of room to play around with inside
> the RCX, and Java was developed in an age where memory limitations were largely
> being looked at as superfluous on account of ever-diminishing memory costs. I
> believe that it may make a JVM for the RCX impossible, or at the very least
> impractical. I'd like to be proven wrong, of course.
For the record, up until recently I agreed with you.
However, after hearing further discussions I think it is possible.
The biggest hurdle is probably garbage collection since this is what
causes Java's propensity to "gobble" memory.
The class files themselves are relatively compact. My
original objections revolved around all of the extra stuff they
contain to make dynamic linking, etc. possible. Discussions here
made me realize that the RCX would have to be treated as the JVM
and not just some OS running a JVM. The PC side would be
responsible for loading and validating classes and then transferring
them into the RCX. This does impose some limitations but I think
they are acceptable.
Reflection capability should be removed which will allow
us to get away from keeping method and class names around. These
are prime memory wasters in a non-GUI environment.
I think making a non-compliant JVM as described is definitely
possible. I also think it is alot of work. I wish I had some time
to put into it because it sounds like fun. A little embedded
experience on the ol' resume might be nice too, even if it is only
Lego. :)
-Paul (pspeed@progeeks.com, http://www.progeeks.com)
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message has 1 Reply:
 | | Re: Some comments (long)
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| (...) This is FUD. What causes Java to gobble memory is more likely (a) the amount of header overhead it places on objects (more to do with hashing support than gc, I suspect) and (b), to a lesser extent, the fact that objects are never "expanded" (...) (25 years ago, 8-May-99, to lugnet.robotics)
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Message is in Reply To:
| | Re: Some comments (long)
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| (...) You have reiterated exactly what I expected would be one of the most popular reasons to want to implement a JVM for the RCX. I hope you don't think I'm against what you're attempting to do... it's just that I, like Kekoa, believe that the (...) (25 years ago, 6-May-99, to lugnet.robotics)
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