Tjaart van der Walt wrote:
> > Realtime clock chipz usually have general purpose ram also.
>
> ...and the RTC will be a bonus.
> Do you have any idea what the smallest Dataflashes
> sell for? (in USD).

2Mbit & up:dual buffers
4Mbit D'flash $8.95 NZ
8Mbit D'flash $16.98 NZ
16Mbit D'flash $28.68 NZ
REC prices, halve for USD

>
> I haven't written a parser/interpreter before, but
> methinks it will be quite a nice challenge.

-PC front end
-parser/interpreter
-BIOS, BIOS options at compile time for memory/pin optimisations
-simulator

The Atmel micro has (IIRC) better pointer operations and can work with
SRAM, if you need speed then this + the D'flash would be far more
powerful as the extra ram would act as a large cache, Mega probably
already has sufficient cache on board for most apps.

As soon as you multitask memory bottlenecks are going to cause major
slowdowns.

I would probably optimise for a certain amount of multitasking by
a) giving maximum standalone capability to each operation (multiple
parameter passing, queued macroinstructions.)
b) Split D'flash pages for multiple task updating per access.
c) Designated frequent tasks stay in RAM
d) Try to align task code tokens with time aligned same page accesses

speed still needs RAM

If you used the ATMEGA then you could fill part of the memory with an
OS, and another part with the command tokens, updating would require ISP
cable and program intervention.

>
> What sort of real nasties should be avoided?
If it is going to be easy to use then try to do a GUI front end like the
STM Actum solutions Realiser, on monitor PLC schematic compiles to ASM
and then hex, wires correspond to data transfer, devices correspond to
dedicated subroutines.  You will probably need multitasking, this will
require dynamic variable space allocation for multiuser tasks. I am not
sure if the Scenix is up to major pointer type operations, Atmel might
be better.  I have considered a CPLD/Scenix/Atmel embedded processor to
provide a kind of DMA function

regards,
Graham
--
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internal combustion engine would require recovery of waste heat by
transfer just before top dead centre then fashion becomes rather
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