16 May
2005
16 May
'05
2:12 p.m.
Subject: Re: Tandy T100 info
From: John Hogerhuis <jhoger at gmail.com>
Date: Mon, 16 May 2005 13:59:50 -0700
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
The basic idea is that Remem implements in CPLD a memory management
unit dividing the 64K address space into 64 1K blocks (actually more
than that since the option ROM is emulated). So you can map any 1K
block from anywhere in RAM or flash into the 64K address space any way
you like.
Ok, the usual MMU only fairly fine grained. Does any apps make use of
that kind of MMU and space?
For compatibility it also emulates a 256K
"Rampac" which is a vintage
external device that hooks to the I/O bus port on a T102.
unfamiliar.
There are multiple MMU maps selectable via an I/O
instruction for
fast-switching of virtual Model 100 environments. So for example you
can have one map with a native Forth-in-ROM, and a couple of maps with
the standard ROM but distinct RAM portions (the latter much like the
"banks" in a T200 or NEC 8300 laptop)
Ok, I've done this on other systems and S100.
Each block in the map can be marked read-only so that
if you are
emulating ROM with RAM or flash you get a perfect emulation, i.e. any
writes against ROM don't get applied.
Handy!
Now I understand what it is and the basic logic inside. Like many MMU
based 8bitters the addition of large ram is usually to emulate disk.
I'm curious to see if any actually do swaping or overlay so the app
can access a larger space or larger data. The reason for that is
most cases that is rare or not even done.
Allison