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From: arsen@sparkyfs.istc.sri.com (Tom Arseneault)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: 1.44M 3.5 disks  //  floppies as swap space
Message-ID: <32535@sparkyfs.istc.sri.com>
Date: 8 Aug 90 02:16:05 GMT
References: <1990Jul31.165603.20869@msuinfo.cl.msu.edu> <1407@wet.UUCP>
Reply-To: arsen@sjc.itstd.sri.com.UUCP (Tom Arseneault)
Organization: SRI International, Menlo Park, CA 94025
Lines: 51

In article <1407@wet.UUCP> nut@wet.UUCP (adam tilghman) writes:
>completely impossible.  If you have installed a 68010 in your ST (I tried
>it, and was in the process of hacking TOS to work with the '010, but lost
>interest), there MIGHT be a way to do it (the 68010 has some _really crude_
>method built-in for handling memory swaps).  If you somehow shove a 68030
>into your ST's 68000 socket, you would then be able to use the '030's
>built-in PMMU (paged memory management unit) to do the dirty work for you
>(the "Virtual" INIT for the Mac does this, and I would assume something
>similar could be whipped up by some intrepid ST programmer.
>
>  Adam Tilghman

Why not try the 68070 from Signetics. I have only read the data sheet
but it seems to be a nifty chip, it has a built in mmu (a little
limited in that it will only handle either 8 2Mb pages or 128 segments
of up to 128kbytes each, I may be reading this wrong but I'll need the
hardware manual to find out for sure), 2 DMA chanels, a UART, and a
I^2C interface (a syncrounos serial port). It uses a 30Mhz xtal but
cuts it in half for internal use so it runs at 16Mhz. It is in a
84-Pin PLCC package and the pins are mostly the same, a few extras to
handle the internal stuff. It is supposed to be object code compatible
with the 68000 and costs about $50 small quantity.

This could be an interesting hack, using a jato board to get upto
running at 16Mhz with out killing the ST and to supply a 68881. You
would then mount the 68070 some support electronics and the jato board
on another daughter board and voila you have a ST with unlimited
virtual memory (a lot of patching to the operating system of course so
that the machine will allow memory access above 4Mb with out an error,
or trap the error and use it? And to allow swapping). You can then add
another serial port (2 if you want to use the I^2C lines), rewrite the
file system to use one of the DMA ports (will speed up the file system
when using multitasking systems) and lots of other things I have not
even touched on. This is all assuming that you could even interface
the 68070 to the ST, should be possible but its the hidden gotchas
that hurt the most.

A point of fact, the _really crude_ method mentioned above is nothing
more than allowing the 68010 to restart an instruction after servicing
a bus exception. A 68000 will start on the next instruction and you
will lose the previous instruction witch will probably result in your
system crashing in massive flames. I rather resent Motarola for say
that it "supports Virtual Memory/Machine" when infact you still
require a MMU to do that stuff.

Anyhow this was just my thoughts on how one might realy screw up a
perfectly good ST.


Thomas J. Arseneault
arsen@itstd.sri.com