[Coco] CoCo2 RAM upgrade idea questions

[David Linsley]

There was a post about the Dragon mod to add 256k and patch L2, a few months ago. I've copied it below:

From: Ken H. <dragon.atv at gmail.com>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Sun, Nov 30, 2014 2:24 pm
Subject: Re: [Coco] Design files for 512k or more CoCo3 upgrade


There was a 256k upgrade for the Dragon / CoCo2 which was published back in
1989 by Bob Hall in the Dragon Update newsletter.

It's based on 256K with 8k pages, just like the CoCo3, which allowed to run
Tandy OS9 Level 2. That makes it much more useful than the banker board.

Here is the series of articles which include the schematics and OS9 patches
(the final 256k design is at the end):
https://drive.google.com/file/d/0B9wgnqGFDmhka2JLS1hrUDhJVEU

Ken


-----Original Message-----
From: "Gene Heskett" <gheskett at wdtv.com>
Sent: ‎1/‎23/‎2015 6:00 PM
To: "coco at maltedmedia.com" <coco at maltedmedia.com>
Subject: Re: [Coco] CoCo2 RAM upgrade idea questions

On Friday 23 January 2015 20:01:15 Allen Huffman did opine
And Gene did reply:
> > On Jan 23, 2015, at 6:12 PM, Zippster <zippster278 at gmail.com> wrote:
> > 
> > What size RAM bank would be best to swap in and out the 64k
> > addressing space from the extended memory?
> 
> The CoCo 3 swaps out 8K blocks. If that were doable, perhaps porting
> OS-9 L2 to the CoCo 1/2 would be possible. Interesting.
> 
> > From the programming (OS9) point of view, what is the preferred
> > method of handling the bank switching?  And how has it been handled
> > in the past with ram upgrades on the CoCo1/2?
> 
> I never knew anyone with an upgraded CoCo, but I recall ads in Rainbow
> advertising upgrades "up to 8mb" back then. Wild.
> 
> > What would be the best amount of total memory?  2mb?
> 
> Does anyone even make >512MB upgrades for the CoCo 3 these days?
> 
Not that I am aware of.  I have a 2 meg disto kit though, works very well 
indeed.  The problem is in designing the addressing latches to add the 
last 3 bits to the gime mapping, doing it in parallel with the gime's own 
logic, with minimum timing skew between the gime bits output and the added 
3 bits so as not to confuse the memory.  Tony may even have used the same 
buffering scheme for both sets of bits so that it all switched fast enough 
not to screw up the memories latching skew.  I have schematics, but I'll 
guarantee they are wrong, Tony never published anything that was 
absolutely accurate.  He treated his schematics that went out like a 
cartographer does his artwork.  Copyrighted mistakes. :)

> > What would be the best version of OS9/NitrOS9 to run on a CoCo1/2
> > with extended memory? Level 2?  Level one is for just 64k systems?
> 
> Level 1 wanted a flat memory map. The modern OS-9/68K/PPC/etc. is Level
> 1, using the MMU only for memory protection (if the system has it).
> Level 2 was the one that used an MMU to remap memory.
> 
> I wish I could remember more.

So do I, I was asked when I went to the garage to work on that chest for 
an hour or two after dinner, to please turn off the air compressor before 
I came in, so of course I forgot it, and just caught a bit of static from 
the LW. Short term memory loss at 80 yo is a real problem folks. :(
 
> 		-- A


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>
US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS

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