Re: lua - running bytecode from an external ram space

[KHMan <keinhong@...>]

On 7/14/2011 12:59 AM, James Graves wrote:
> imo wrote:
> > Hi, as the Lua is a virtual machine based, let me kindly ask you
> > following:
> > 1.would it be possible to allocate the vm “working space”, or some
> > parts of it (e.g. tables, functions) to an external ram, accessible
> > to Lua via a c-interface, like:
> > long ram_rd( long address);
> > void ram_wr(long address, long data);
> > so we may use _any_ type of an external ram (e.g. serial spi sram,
> > fram) for running Lua byte code of almost _any_size_ then?

The problem with this item is, the only serial SPI SRAM parts IIRC 
seems to be those two Microchip parts; 23A256 is 32KBytes only. 
Bigger 'uns and you'll start to need lots of I/O pins.

Might as well stick to a 32-bit part with >=64KB RAM. I bought a 
few recently, USD3.44 per piece. Nowadays it's hard to beat 
single-chip choices with a multiple chip scheme.

But if the OP can find FRAM of a few Mbits, I want to grab some 
too! :-)

> > 2. is it even feasible to find such points in the Lua source code
> > where we can interface such an external ram?? Or it would require an
> > rewrite of the entire vm?
> > This may enable to run even very large scripts on small ucontrollers
> > (e.g. with flash>128kB and ram>16kB) when speed is not a priority.
>
> This will require significant changes to the Lua VM, and I don't think
> it will be worth the effort.  You say speed is not a priority, but
> running  Lua on a microcontroller _that_ small with so little memory
> will be very, very slow.
> [snip]

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