[Coco] [magervalp at gmail.com: Re: 6809 assembly knowledge needed]

[Gene Heskett]

On Thursday 07 January 2010, John W. Linville wrote:
>Cool comment regarding 6809 on the cbm-hackers list -- I thought
>y'all might enjoy...
>
Chuckle.  Having looked at the available architectures circa 1982-5, I was 
convinced long ago that both the z-80, 8080 and the 6502 variants, were quite 
drain bamaged, and that the 6809 was by far the smartest cpu around at the 
time.

There are some other odd architectures out there, the 1802 from RCA, and the 
9900 from TI come to mind.  The 1802 wasn't a pic processor but could have 
been made that way by careful but slow programming.  I didn't use that 
however when I wrote an application for an 1802 that survived in the KRCR-TV 
control room for over 15 years.  The 9900 used local memory for its image of 
its registers, and could switch contexts in a single instruction simply by 
reloading its register pointer to a different process's register image.  The 
stopped process had no knowledge that it had been stopped, even if the 
stoppage was weeks in duration.  When resumed, it simply resumed at the next 
instruction fetch.

The advent of PIC programming was, IMO, a watershed moment in computing 
history.

>----- Forwarded message from Per Olofsson <magervalp at gmail.com> -----
>
>> Date: Thu, 7 Jan 2010 10:38:28 +0100
>> From: Per Olofsson <magervalp at gmail.com>
>> To: cbm-hackers at musoftware.de
>> Subject: Re: 6809 assembly knowledge needed
>>
>> On Thu, Jan 7, 2010 at 7:47 AM,  <ruud.baltissen at apg.nl> wrote:
>> >> According to http://en.wikipedia.org/wiki/6809 this ....
>> >
>> > Many thanks for the conformation! But AFAIK this is the only reentrant
>> > related code for accessing a table. And a meager one IMHO; it is
>> > equivalent to LDA Label / LDA [Label] ie. you can only address one
>> > value. And I wonder if the indirect instruction is of any use: if
>> > "Label" is part of this reentrant code, what value should the compiler
>> > calculate? I think I'll take Jack's advice to consult the FLEX group.
>>
>> Position independent code is a huge boon for drivers & libraries, and
>> on operating systems where everything doesn't load at a fixed address
>> also whole applications. For example this:
>>
>>   http://www.6502.org/users/andre/o65/fileformat.html
>>
>> would be mostly redundant on 6809, and would have saved André, Daniel,
>> and Uz a lot of work (and together with drivecode was one of the
>> things that tripped me up with SMOS). Just take a look at OS-9,
>> there's a reason we never got anything as advanced as that for the
>> 6502 or Z80 (well, until the late 90s :).
>>
>> On C= 8-bits its use is a little more limited, but would still be
>> handy e.g. for decrunchers and drivecode.
>>
>> Anders Carlsson wrote:
>> > Of course I could get me a cheapish Dragon 32 or similar if I really
>> > wanted the 6809 covered.
>>
>> Don't forget the Vectrex!
>>
>>        Message was sent through the cbm-hackers mailing list
>
>----- End forwarded message -----
>


-- 
Cheers, Gene
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