processors and FP (was: OQO)

Richard A. O'Keefe ok at cs.otago.ac.nz
Thu May 16 05:40:02 UTC 2002


Tim Rowledge <tim at sumeru.stanford.edu> wrote:
	> How about the Jazelle bytecode accelerator which will be standard (I
	> think) on ARM11 (http://www.arm.com/armtech/jazelle?OpenDocument) ?
	> Would that help Squeak?
	Yuck. I doubt it to be honest. Even for java it doesn't really do very
	much. Last time I read the documentation it pretty much claimed that it
	could run jave faster than a simple interpreter vm but not as fast as a
	hotspot-like system. They semed to be aiming art embedded situations
	where a couple of times faster was valued and lots of ram was
	impossible; cellphones etc.
	
There are some interesting things about Jazelle.
The fact that they added Java support to an existing design with
just 12k extra gates is pretty good.
The fact that they've got the three instruction sets (ARM, Thumb, JVM)
in a core that designers can embed in other System-on-Chip design is
likely to make it very attractive.
I strongly suspect that they were concerned with electrical power use
at least as much as RAM.

The performance problem with Jazelle is simply that the JVM wasn't well
designed for execution; they're doing about as well as you _could_ do
executing JVM instructions one at a time.

Something like Transmeta's Crusoe or IBM's DAISY (both of which involve
on-the-fly translation of many instructions into VLIW) would be required
to get much better speed.



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