Re: lua - running bytecode from an external ram space

[David Walker <dbwalker0min@...>]

Another option could be pymite
(http://code.google.com/p/python-on-a-chip/). I haven't used it
personally, but I know it can run code from external SPI-based
devices.

On Wed, Jul 13, 2011 at 10:35 AM, KHMan <keinhong@gmail.com> wrote:
>
> 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
>