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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 ( may not have soon in such capacity, though).
[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... :-(

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