Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!think!husc6!uwvax!astroatc!johnw
From: johnw@astroatc.UUCP (John F. Wardale)
Newsgroups: comp.sys.nsc.32k
Subject: Re: kit wishlist and software
Message-ID: <926@astroatc.UUCP>
Date: 31 Mar 88 03:34:45 GMT
References: <880@PT.CS.CMU.EDU> <177@anumb.UUCP> <585@naucse.UUCP> <1006@ur-tut.UUCP> <23506@hi.unm.edu> <537@taux01.UUCP>
Reply-To: johnw@astroatc.UUCP (John F. Wardale)
Organization: Astronautics Technology Cntr, Madison, WI
Lines: 46
Keywords: 32k kit, cheap unix.

In article <537@taux01.UUCP> orr@taux01.UUCP (Orr Michael ) writes:
>In article <23506@hi.unm.edu> cyrus@hi.unm.edu (Tait Cyrus) writes:
>>
>> ... External Call stuff is *SLOW*

> are slow , BUT, they provide a unique capability. The way this works 
> is that you can generate code that is totally free from relocateable 
> addresses. All references to entities visible across modules is done 
> utilizing "link tables". This makes it possible to change one module,
> with out making it necessary to re-compile all other modules. In ROM 
> based application (for example) this makes it  less expensive, as you
> have to replace fewer ROM chips.

Close, but *NO* cigar!   The "CXP" insturction requires an
"External Procedure Descriptor" (see below).
Each module has a "link table" wich is a list of EPDs used by that
module.
Now if you change ONE routine in ONE module, you will shift *MANY*
routines in that module. 
For each routine that's moved, you must:
   change its EPD in *EACH and EVERY* module that calls it.

--> Bassically, "relink" the world!

E.P.D = (the 16-bit address of the callED's MOD-table , 
         the 16-bit offset of the called proceucure entry)

- = - = - = - = - = - = - = - = - = - = - = - = - = - = -

Having a "link table" for each module is DEFINATLY a lossage for
"ROM-ability" and the rest is just TOO slow!

There are better alternatives, but ONLY if you can change the
architecture.

1:  make a "user-service-call" instruction that takes a *NUMBER*
    like an "SVC" instruction. (or a mod#, function# pair)
	....maybe add a "Call-Look aside-Buffers" (cache) for speed.
2:  Indirect procedure calls (see the Mac stuff)
3:  RISC arguments: Do you even NEED normal "call" insturctions?
	(Personally I like the MIPS stuff)

-- 
					John Wardale
... {seismo | harvard | ihnp4} ! {uwvax | cs.wisc.edu} ! astroatc!johnw

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