Re: lua - running bytecode from an external ram space

[KHMan <keinhong@...>]

On 7/14/2011 2:42 AM, imo wrote:
> Yea, I did of course a proof of concept.. I've connected 2mbit
> FM25H20 (256kx8) serial SPI FRAM to a pic24HJ. You can access
> randomly a long (32bit) for r/w in ~8usec.

Yummy, nice FRAM you have there. :-) Here IIRC I see a lot of it 
marked as "discontinued product" in the usual local catalogs.

> With a pic32mx (I am
> running the pic32lua on it) or an arm or other fast small chip you
> may get today ~2usec for the r/w access to a random long placed in
> the SPI Fram (i.e. most serial memories have 20-66MHz spi clock).
> Moreover, with such "virtualisation" via those C r/w calls you may
> access any _other_ kind of external RAM with a proper HW interface.
> Imagine you may run Lua bytecode on a pic32mx or other chip (with
> on-chip 128kB flash and 32kB ram as a minimum) and run a xxMB big
> script in it :). Of course slower than running it in the internal
> ram (..you may not have soon in such capacity, though).
> -imo
> [snip snip snip]

True, it can be done, but it's not a scenario that has a lot of 
critical "must be done this way" applications driving it. For 
MCU-style projects, compiled scripts likely won't run into 
non-manageable sizes. Often it's data that's big and usually Flash 
is enough to satisfy those needs. Others on this list have done 
great work optimizing Lua to use program Flash memory etc.

Would be nice to see an implementation of it, but I fear it is 
looking like an solution seeking an application. :-)

Unfortunately, all this "good enough" scenarios are also giving 
techs like FRAM and PRAM a bit of trouble with fulfilling the 
promise of massive adoption... :-(

--
Cheers,
Kein-Hong Man (esq.)
Kuala Lumpur, Malaysia