[maemo-developers] Java acceleration/Jazelle

[From: Larry Battraw]

On 7/17/07, Simon Pickering <S.G.Pickering at bath.ac.uk> wrote:
> Hi Scott (& all),
>
> > The following describes an experiment I suggested:
> > Create an array with opcodes 204 to 255 in it.  Create one handler for
> > all opcodes.
> > Set up R14 to point to opcode 204.
(snip)
> I sat down and wrote a bit of code that I hope will do this
> (eventually). The one issue I've not sorted out yet is how to print
> something to the screen from assembly. Is there some secret incantation
> (CALL for example), or do I need to define my own printf function in
> assembly)?

A couple thoughts from a former hardware hacker here: first, serial
ports are your friend so if you can find a sacrificial device that has
a cracked screen or some other serious but non- life-threatening
defect you should probably invest in a level-shifter chip and a DB-9
connector (and some soldering cleverness) to be able to communicate
through the serial port.  Sending bytes back and forth that way is
trivial and will allow you to seriously goof around with an otherwise
worthless device at the kernel or bootloader level.

  The second thought is learn the ABI convention for calling C methods
from assembly and you can pass whatever data you need to a function
that will do the printing for you.  I'd suggest going with this route
since it will be the most straightforward without soldering but also
the least versatile.  --You may end up rebooting many, many times and
the less overhead there is to initialize before playing around the
faster you can try a new idea.  At any rate, I believe the ABI changed
when we went to the armel format and so there's a handy description on
changes to system calls and so forth here:
http://wiki.debian.org/ArmEabiPort  Sorry if I'm pointing out anything
that might be obvious, these are just things I had to work through
when I was working on this type of thing on OS-less boards.


> http://people.bath.ac.uk/enpsgp/nokia770/jazelle/test_jazelle7.c
>
> > Simon, you have done a great deal of work, and gotten quite far.   Good
> > work!
>
> Many thanks and thank you for your detailed summary of the patent, it's
> good to have you on board,
>
>
> Simon

Good luck!
Larry