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From: ForthNet@willett.pgh.pa.us (ForthNet articles from GEnie)
Newsgroups: comp.lang.forth
Subject: ANS TC Magnet for ROMability
Message-ID: <2768.UUL1.3#5129@willett.pgh.pa.us>
Date: 15 May 91 02:10:22 GMT
Organization: (n.) to be organized.  But that's not important right now.
Lines: 47

Category 10,  Topic 22
Message 35        Mon May 13, 1991
B.RODRIGUEZ2 [Brad]          at 23:25 EDT
 
Re. Jack's proposals for ROMability: I agree, and disagree.

We've found this capability very useful in embedded systems. However, we
usually need more than just two address spaces (RAM and ROM).  For this reason
our metacompiler includes the defining word
 DICTIONARY, which resembles VOCABULARY in some respects:

    start-adr end-adr DICTIONARY name

defines a named dictionary with its own dictionary pointer, and then later
invocation of 'name' makes that dictionary current.  Rather than set a flag,
we define a "dictionary-pointer-pointer" 'DP which holds the address of the
current DP.  Thus,

    : DP 'DP @ ;

and HERE, ALLOT, and such will follow.  Of course, 'DP can be a user variable,
but all of the dictionary pointers should be in common RAM (shared among
tasks).  This scheme can conform to the RAM and ROM usage, e.g.,

HEX 0 8000 DICTIONARY ROM
 8000 FFFF DICTIONARY RAM       \ or any other address limits

but is much more powerful.  It is very nice for supporting paged memory
systems.  We're even working on parallel compilation of separate programs
(where two CPUs need to know each other's symbol tables) using this technique.
There are refinements for extended addressing and physically separate memory
spaces.

Jack's right...this concept is VERY useful, and good Forth.  But I hope this
example shows that it's too soon to move RAM and ROM into the "normative"
status.

- Brad
 Brad Rodriguez        | brad%candice@maccs.uucp      (God willing)
 B.RODRIGUEZ2 on GEnie | brad%candice@maccs.dcss.mcmaster.ca
 "Shoes for industry!" | bradford@maccs.dcss.mcmaster.ca  (archaic)

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