[Coladam] SW roms

Geoff Oltmans geoff at oltmansfamily.org
Fri Apr 2 05:09:41 CEST 2010

Ah, that's a good point. I hadn't considered that the SW code would attempt to swap back out to the ROM space rather than the RAM. Might take some patches as well, if they could reasonably be done.

On Apr 1, 2010, at 6:38 PM, Rich Drushel wrote:

> On Thu, April 1, 2010 2:49 pm, geoff at oltmansfamily.org wrote:
>> I'm not sure I agree. According to the Adam Technical Manual, the MIOC can
>> be set up where the Smartwriter ROM (in the low 32k address space) is
>> replaced with 32k system RAM.
>     Hi Geoff, there are configurations to mix/match ROM and RAM address
> spaces.  But if you are running a SW ROM image from RAM, then you have
> to trap all the cases where SW is trying to swap back to itself in ROM.
> Writing code to use multiple address spaces is tricky, as you have to
> be sure to be running code from one 32K while only swapping out the other
> -- otherwise poof your code vanishes.  You can however load up sequential
> banks of XRAM with the same code at the same address space, so when the
> bank switches, it is still going to execute the same instruction.  RAMdisk
> code has to do tricky stuff like that.
>     What I am sure you can't do is have an XRAM configuration where the
> low 32K is from one bank and the high 32K is simultaneously from another.
> E.g., low 32K from bank 0, high 32K from bank 1.  If you have put your
> SW ROM code into the low 32K to run it from there, as a shadow ROM, then
> you could only use the high 32K of XRAM for other purposes.  SW from ROM
> is expecting to be able to use both low and high 32K of bank 0 of XRAM
> for extra workspace.  It does this by moving some code bits into the
> banks to handle switching problems as described above.  SW does not know
> about any XRAM other than bank 0 (as 128K and up XRAM were aftermarket
> and need additional hardware to provide a separate XRAM bank-select
> port -- originally part of the Orphanware parallel interface, also available
> as an "addresser card").
>     Thus, the easiest way to get SW to run from XRAM is to patch all
> the code that does bank-switching to put the SW ROM into low 32K, with
> the value to make that the low 32K of XRAM, and disable SW's own detect
> of XRAM (bank 0 = 64K), to prevent it from trying to use XRAM as a
> document buffer at all.
>     I haven't looked over the SW code in detail for awhile, but this is
> to the best of my recollection (and also experience with RAMdisk drivers,
> which are elegant when they work but tricky to write).
>     *Rich*
> -- 
> Richard F. Drushel, Ph.D.            | "They fell:  for Heaven to them no hope
> Department of Biology                |  imparts / Who hear not for the beating
> Case Western Reserve University      |  of their hearts."
> Cleveland, Ohio  44106-7080  U.S.A.  |         -- Edgar Allan Poe, "Al-Aaraaf"
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