Subject: Making 0x0000-0x3FFF swappable?

From: "Jeff" <fyberoptic1979@...>
Date: Thu, 06 Sep 2007 23:26:20 -0000

How hard do you suppose it would be to make the first 16KB of address 
space swappable, like the middle two "slots" can do?  I haven't gone 
over the circuits hardly at all so I don't know really what does what 
at the moment.  But if it wasn't too elaborate, and one could take 
advantage of some spare port or something like that, it might be 
worth trying.  Even if I had to hard-wire the page of ram it went to, 
that'd be okay too.  And I know there's some undocumented pins on the 
CPU still.

In FyOS, I've written in compatibility for almost all of CP/M's BDOS 
function calls except file operations.  Eventually I want to get that 
too.  But the point is, most CP/M apps naturally expect to run from 
0x0100.  They call 0x0005 for BDOS functions.  These two aspects 
alone aren't TOO bad; I mean, with a little work, one could relocate 
a program to run at 0x4000 instead (which I've been doing to one for 
testing purposes)

But obviously there's much more than simple relocation most times, 
since various apps can have hard-coded memory locations and routines 
that do things in places that'd require digging really deep in the 
code, and truly learning what every aspect of the code is doing.  A 
very time consuming and outright confusing chore at times.

So, obviously, I opt to take the easy way out if possible!  I'm not 
calling any firmware functions at all, so I don't need anything from 
the first 16KB of address space once FyOS is running.  If I could 
just swap ram there, it would be a much more functional system.  So 
I'm mostly wondering if anyone has examined the hardware enough to 
determine if this is very possible?