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Thread: Tethered and Embedded Forth
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face BY : Byron Jeff email (remove spam text)



On Fri, Jan 23, 2009 at 01:00:20PM -0500, Marcel Birthelmer wrote:
> Hi all,
> I'm interested in the process of deploying a light/tethered forth to an
> embedded target. The architecture in question is MIPS-based, but that
> shouldn't matter at this stage, I think.
> I've been reading ( http://pygmy.utoh.org/3ins4th.html ,
> http://www.bradrodriguez.com/papers/moving1.htm ), but so far, I haven't
> been able to find a simple tutorial-style method of deploying a tethered
> forth (with the forth "compiling" actually taking place on the host CPU).
> If anyone has an experience or resources regarding this process, I'd love to
> hear about it.

Typically in a tethered situation the dictionary stays on the host while
the compiled code gets transferred to the target. The problem with Brad's
paper is that it's designing for a completely self hosted FORTH on the
target machine.

One of the best descriptions I've seen so far is the Embedded Systems
chapter in Stephen Pelc's "Programming Forth". You can find a copy here:

http://www.mpeltd.demon.co.uk/arena/ProgramForth.pdf

The 3 instruction forth represents a minimal starting point. But in reality
there isn't enough of a kernel to really get any traction.

The short of it is that you need to accomplish two tasks early on:

1) Define and implement a set of core primatives on the target.

2) Create a dictionary and a target compiler on the host.

Remember that at a fundamental level that a trivial FORTH is nothing more
than a list of addresses to the words you want to execute. So the
dictionary needs to know the address of the word on the target and the
compiler replaces each word it compiles with the address of that word on
the target.

So start with your primative set and work your way out from there.

Hope this helps. I'll hang around this thread if you have any more
questions.

BAJ
<20090123144909.GA23655@clayton.edu> 7bit

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