Question about Jazelle on Cortex A15


MTPDA

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So I was thinking about uses for the M4 chips and was looking at the Wikipedia page for ARM architecture (Specifically the Thumb programming part) to see if it would be difficult to learn so I could try playing around with it. It mentioned Jazelle as a minor alteration on Thumb-2 for executing Java bitecode. The Wikipedia page for the Cortex A15 Series says it supports "Jazelle RCT for JIT compilation" does that mean someone more knowledgeable than me could code say a program for watching for incoming calls using Java and execute it on the M4 or am I misunderstanding something?
 

levi

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Jazelle RCT is a very different beastie from Jazelle. Jazelle would theoretically at least make the CPU run old java bytecodes itself, but that's no longer done, because Java ME is no longer worth bothering with for phones and that. Jazelle RCT apparently just adds a few checking modes to existing Thumb instructions. I guess it's meant to make it easier to compile Java things down to Thumb code, but I'm not sure why anyone would bother writing in Java for machine compilation to be honest.

There's also the problem that we don't quite understand how to drive the M4s yet. Someone needs to figure that out first.
 

MTPDA

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Jazelle RCT is a very different beastie from Jazelle. Jazelle would theoretically at least make the CPU run old java bytecodes itself, but that's no longer done, because Java ME is no longer worth bothering with for phones and that. Jazelle RCT apparently just adds a few checking modes to existing Thumb instructions. I guess it's meant to make it easier to compile Java things down to Thumb code, but I'm not sure why anyone would bother writing in Java for machine compilation to be honest.

There's also the problem that we don't quite understand how to drive the M4s yet. Someone needs to figure that out first.
Ah, I kinda figured it seemed too good to be true. Thanks @levi!
 

lukey

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Also, someone would have to put a huge effort in to make it work, just so you can run a few lines of java code on it. Why not program in C in the first place?
 

netcat

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I first noticed this "java" in /proc/cpuinfo of my lego mindstorm and have been curious ever since.

1622228477995.png
 

MTPDA

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Also, someone would have to put a huge effort in to make it work, just so you can run a few lines of java code on it. Why not program in C in the first place?
I'm not a programmer. I took some programming classes (html/css/JavaScript, C/C++/C#, ect) years ago but never got around to using it. I just assumed that Thumb was a programming language and was curious when I saw the mention of Java bytecode being executed on bare metal and assumed it was more efficient.
Post automatically merged:

I first noticed this "java" in /proc/cpuinfo of my lego mindstorm and have been curious ever since.

View attachment 37192
Oh man! I remember the mindstorms fondly! I personally had an NXT and my high school had the yellow one, don't know which model if there was different yellow ones.
 
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