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From: emjej@uokvax.UUCP
Newsgroups: net.micro.trs-80
Subject: Re: CoCo Memory Expansion
Message-ID: <38800003@uokvax.UUCP>
Date: Tue, 3-Dec-85 14:00:00 EST
Article-I.D.: uokvax.38800003
Posted: Tue Dec  3 14:00:00 1985
Date-Received: Fri, 6-Dec-85 07:09:17 EST
References: <405@ucdavis.UUCP>
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Nf-ID: #R:ucdavis.UUCP:405:uokvax.UUCP:38800003:000:1769
Nf-From: uokvax.UUCP!emjej    Dec  3 13:00:00 1985


/* ---------- "CoCo Memory Expansion" ---------- */
  I have heard over and over that it is impossible to bank extra
RAM in the CoCo without dragging the entire operating system with
you when you select a new bank....[Proposal to access/select
additional memory via memory-mapped I/O, if possible] If [it is
possible], could OS9 use this extra memory?

					       - Mark Nagel
/* End of text from net.micro.trs-80 */

It would be hard to use such memory for anything but device drivers, unless
you're talking something that does real live memory mapping of the kind that
Level Two wants.  I don't know enough to say whether it's hardwarily pos-
sible, although something like that is how Level Two systems (and SS-50C
bus boxes) work, I think--one uses memory-mapped I/O to control the memory
mapping hardware.

The problem would be how to support the "link" operation (handing a process
a pointer to a specified module) in the face of that kind of memory.  If
you let some modules live in the stock memory and some here, it could be
nasty.  (If there are, as I strongly suspect, other pitfalls as well, I
invite corrections and addenda!)

That is *NOT* to say it's not worth doing--it would be wonderful to
be able to move graphics pages out of the memory one uses for modules,
or to do real live caching to minimize the effect of the cretinous CoCo
disk controller on CoCo performance.  (That's what's *really* depres-
sing about Tandy's slowness in coming out with a 6809 box not hamstrung
by a design that was probably OK for a single-user game machine running
Microshaft BASIC--if you've seen a SSB or Gimix box running OS-9, or if
you're among the VERY lucky, a Fujitsu FM-11, you know it could utterly
blow away far more expensive machines.)

						James Jones