Re: lua on ARM7

[Asko Kauppi <askok@...>]

Yes, Bert's situation sounds challenging (maybe to the degree of  
foolishness? :) to say the least.

I would consider doing an "event dispatch" interrupt handler (in C)  
that would sit in the other end of a FIFO queue, the other end being  
polled by Lua (can you run one instance, as the main loop?) to take  
in "commands". Of course, those commands can be full  Lua scriptlets,  
nothing's preventing that. But the point would be, you end up having  
them in the queue, so getting multiple interrupts won't be an issue  
(unless the queue grows and grows and... then you have too slow a CPU  
anyways ;)

Hope this helps, still thinking you'll never fit Lua in 30kB  
binary. :P  Please prove me wrong.

-asko


David Brown kirjoitti 15.5.2006 kello 14.19:

> 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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