[Coco] 6309 microprocessor project 01-16-2004

[John Collyer]

Roger you got it exactly right!  Now that sounds sweet.
I'm impressed with your idea on the V register! Compiler
writers take a note here.

John Collyer

----- Original Message ----- 
From: "Roger Taylor" <rtaylor at bayou.com>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Saturday, January 17, 2004 11:48 PM
Subject: Re: [Coco] 6309 microprocessor project 01-16-2004


> At 04:48 PM 1/17/2004 -0500, you wrote:
> >I just talking didn't mean to cause alarm.
> >
> >A&B could still equal the lower 16-BITS of D.
> >E&F could still equal the lower 16-BITS of W.
> >Q could still equal D&W, but the lower 32-BITS of Q.
>
> A 64-bit Q register.  Sweet.
>
> By the way, there's some comments in Chet and Alan's 6309 ref guide that
> kinda talk down just a tad about some of the feaures in the 6309 and how
> unuseful they are, but I have found that there are many good uses for
> everything they added to the 6309.
>
> One of the simplest things that was given is a brand new register called
> V.  There's a 16-bit V register and we can't find a use for it?  The first
> thing I thought of was "V for variable" pointer.
>
> One use could be exactly like how the EBP register works on the PC.  You
> push some parameters to the stack, call a procedure, and on entry into
that
> procedure it makes a copy of the stack location into V, then makes more
> room on the stack for local data.  Because we know what side of V our
> parameters are on, and the side that our local data is on, we can
reference
> everything using [-/+offset,V]  (*I think*)... I have not verified this
> yet, but it looks legal.  Everything on the plus side of V should be our
> local data since it was pushed last, and everything on the negative side
> should be our parameters.  Naturally, a compiler would compute these
offsets.
>
> It might not sound like there's a logic behind this, but I have plenty of
> docs that say otherwise, so if the EBP register has this one role on the
> PC, then perhaps the V register on the 6809 could take advantage of any
> advantages there might be. :)
>
>
> ----------
> Roger Taylor
>
>
>
>
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