Re: lua on ARM7

["David Brown" <david@...>]

Hi Bert,

I haven't done much with Lua yet, but I've plenty of experience with
embedded systems.  Calling an interpreted language from an interrupt running
at that speed sounds like a bad idea.  30 kHz is pretty fast - even for an
ARM.  Depending on the type of ARM and its clock speed, you have something
like 1000 to 10000 clock cycles between interrupts.  That's not a lot when
you are running an interpreter.  At best, you will use a large proportion of
your cpu time, and will get very large jitter.  In particular, garbage
collection may cause occasional extra delays.

If you really need to run lua scripts triggered by interrupts, you are
probably better off setting a flag in the interrupt routine, and using that
to start the script from within your main loop.

mvh.,

David



----- Original Message -----
From: bert
To: Lua list
Sent: Monday, May 15, 2006 9:05 AM
Subject: Re: lua on ARM7


Hi All,

thanks a lot for the helpful replies. I tried compiling LUA and it is true
that I end up at over 30K but less than 64K of code. that is compiling in
thumb mode so I suspect that it will be even more if I try ARM mode. I have
tried with the IAR EW compiler, still have to try the GCC.

Now, the firmware would be running LUA code in an interrupt. How would this
be done to keep things thread-safe (nested interrupts?), and is it realistic
to call a LUA function from an interrupt routine being called at 30kHz?

It somehow makes more sense to me to compile the LUA code on my host PC to
something that can be run very efficiently on the ARM platform, like native
code, but then I'm not sure how difficult it is to compile LUA code to
native ARM directly.

Thanks,
Bert


Luiz Henrique de Figueiredo <lhf@tecgraf.puc-rio.br> wrote:
> What parts of the LUA source code do I need for making
> this work and what can I safely remove?
> This is for Lua 4.0, but may get you started:
>
> http://www.lua.org/notes/ltn002.html

Yes, and Lua 5.x this is even easier. See etc/noparser.c
This will save you some 30% of the core code.
--lhf





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