[N8VEM: 18763] Motorola MC68020 Project Ideas

Discussion:

Sergey

2014-10-03 18:54:12 UTC

Hi,

The short summer in the Pacific Northwest is coming to its end, and I
started to think about projects for the long winter.

I visited a local surplus store yesterday and picked a few MC68020 / 20 MHz
processors with sockets... They were real cheap, and I couldn't resist. :-)

So I am thinking about what should I build with these processors. Here are
some of my ideas:
- It would be nice to build a computer that could run some kind of UNIX.
Unfortunately that means the system will need to have an MMU (and the
matching MC68851 PMMU seems to be an unobtainium). Are there any UNIX-like
systems that would work without an MMU? Any other OS recommendations? OS-9
could be a good fit, but AFAIK it is not free. Or maybe I should implement
some kind of rudimentary MMU (e.g. 74LS612) or use a CPLD?
- It could be a standalone system with processor, memory, several UARTs,
block storage (most likely an IDE compatible flash card).
- Or an extendable SBC with VME or ECB bus. VME seems to be a good fit,
although I want to keep the board size small, so most likely it will be a
single connector 24-bit address/16-bit data VME variety... Here is such a
project: http://www.dutch.nl/bdj/vme/68020sys.htm
- Use 32-bit SRAM memory - four 512 KiB chips. Possibly add a connector for
a memory card for future extension (and to keep SBC small)

Thanks,
Sergey

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Alan Cox

2014-10-03 19:34:38 UTC

Permalink

2BSD UZI and Minix. You ideally want some kind of simple banking unit but
you can build one out of logic gates and/or a fast SRAM. Without it you
can't do a few key Unix things like fork()

For 68020 MMU try old Apple folks. The MacII had a socketed optional MMU.

Alan

Post by Sergey
Hi,
The short summer in the Pacific Northwest is coming to its end, and I
started to think about projects for the long winter.
I visited a local surplus store yesterday and picked a few MC68020 / 20
MHz processors with sockets... They were real cheap, and I couldn't resist.
:-)
So I am thinking about what should I build with these processors. Here are
- It would be nice to build a computer that could run some kind of UNIX.
Unfortunately that means the system will need to have an MMU (and the
matching MC68851 PMMU seems to be an unobtainium). Are there any UNIX-like
systems that would work without an MMU? Any other OS recommendations? OS-9
could be a good fit, but AFAIK it is not free. Or maybe I should implement
some kind of rudimentary MMU (e.g. 74LS612) or use a CPLD?
- It could be a standalone system with processor, memory, several UARTs,
block storage (most likely an IDE compatible flash card).
- Or an extendable SBC with VME or ECB bus. VME seems to be a good fit,
although I want to keep the board size small, so most likely it will be a
single connector 24-bit address/16-bit data VME variety... Here is such a
project: http://www.dutch.nl/bdj/vme/68020sys.htm
- Use 32-bit SRAM memory - four 512 KiB chips. Possibly add a connector
for a memory card for future extension (and to keep SBC small)
Thanks,
Sergey
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John Coffman

2014-10-03 20:44:07 UTC

Permalink

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<head>
<meta content="text/html; charset=ISO-8859-1"
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<body bgcolor="#ffffff" text="#000000">
Sergey, 
 
I've been thinking about a 16-bit 68000 system even before the ECB
Mini-68K CPU board was produced. 
 
A couple of conclusions:  It is easier to interface a 68020 or 68030
to the ECB than it is to interface a 68000 or 68010.  The last two
do not drive A0 -- so byte operations become complicated.  The
dynamic bus sizing on the 68020/030 are very convenient. 
 
Memory probably needs to be on a separate card.  The 4MEM board has
a 16Mhz limit with both the SBC-188 and Z180 Mark IV.  This may be
due to the MMU on-board that card, but any discrete MMU will slow
things down a little.  The integrated MMU on the 68030 becomes
attractive. 
 
My own interest is really "retro," so I still like the idea of a
68000 or 68010; however, the MMU will probably have to be on the CPU
card itself.  So this tends to dictate a double-width Eurocard, like
that one used on the new 6x0x board, a board with an MMU.  (VME is
also double-width Eurocard, but uses 2 connectors, rather than the
ECB single connector.) 
 
My own choice would be to stick with ECB, and to be compatible with
existing peripheral cards. 
 
--John 
 
 
 
 
 
 
 
On 10/03/2014 11:54 AM, Sergey wrote:
<blockquote
cite="mid:c9124431-b940-45b3-a1a1-f2815778d6d1-/***@public.gmane.org"
type="cite">
<div dir="ltr">Hi, 
 
The short summer in the Pacific Northwest is coming to its end,
and I started to think about projects for the long winter. 
 
I visited a local surplus store yesterday and picked a few
MC68020 / 20 MHz processors with sockets... They were real
cheap, and I couldn't resist. :-) 
 
So I am thinking about what should I build with these
processors. Here are some of my ideas: 
- It would be nice to build a computer that could run some kind
of UNIX. Unfortunately that means the system will need to have
an MMU (and the matching MC68851 PMMU seems to be an
unobtainium). Are there any UNIX-like systems that would work
without an MMU? Any other OS recommendations? OS-9 could be a
good fit, but AFAIK it is not free. Or maybe I should implement
some kind of rudimentary MMU (e.g. 74LS612) or use a CPLD? 
- It could be a standalone system with processor, memory,
several UARTs, block storage (most likely an IDE compatible
flash card). 
- Or an extendable SBC with VME or ECB bus. VME seems to be a
good fit, although I want to keep the board size small, so most
likely it will be a single connector 24-bit address/16-bit data
VME variety... Here is such a project:
<a class="moz-txt-link-freetext" href="http://www.dutch.nl/bdj/vme/68020sys.htm">http://www.dutch.nl/bdj/vme/68020sys.htm</a> 
- Use 32-bit SRAM memory - four 512 KiB chips. Possibly add a
connector for a memory card for future extension (and to keep
SBC small) 
 
Thanks, 
Sergey 
 
</div>
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Alan Cox

2014-10-03 21:52:15 UTC

Permalink

The MMU for the 68010 actually adds a wait state to the system as well
as being quite a pain from a software perspective. It's not page based
but variable sized region based. Sufficiently odd that companies like
Sun actually implemented their own MMU in preference, while some
others actually set it up to provide a range of fixed size
"partitions" and put programs in the nearest sized partition rather
than doing paging.

The actual needs for the various Unix clones are something like

2.11BSD 1MB total RAM, memory protection ideally, ability to map
banks of memory (would need porting), swap, no paging, networking
Minix 1.x 512K RAM, no MMU - but fork() is emulated so that aspect
is very slow. Most code works well. No swap or paging, no networking
NetBSD 68020+MMU, about 24MB RAM, paging, networking
Linux 68020+MMU, about 24MB RAM, paging, networking
ucLinux 68000, fork() not supported, about 8-16MB RAM, no swap
or paging, networking

Minix/68K is basically dead but has one determined user left

http://www.beastielabs.net/minix/

That's probably the nearest thing to useful for something with the
spec of the existing 68000 board and its a small community so it will
be easy to get to know everyone 8)

The other options if you didn't want Unix would be to boot something
like EmuTOS, which is a GPL equivalent of the GEMDOS shipped on the
Atari ST, or things like OS9/68K or MinT (MinT is the GPL multitasking
GEMDOS OS that Digital Research forgot to write ;-) coupled with a
multitasking GEM GUI)

There was also an initial port of UZI to the 68K but afaik that never
went anywhere useful. It would however certainly be the smallest
Unixlike option and probably run usefully in 256K !

There are some details on the Sun MMUs and similar designs. They all I
think work on the same basic principle. The low bits of the address
are passed to the row address of the main RAM (150nS or so on a
68010), and in parallel a 50nS or similar static RAM was used to look
up the high bits and then either feed them to the RAM, or generate
BERR and drop CAS so the stray write never happens if it is faulting.
Essentially the same technique every processor today uses to parallel
cache lookup and MMU.

Not unfortunately quite so applicable to a modern SRAM based board.

Alan

Nikolay Dimitrov

2014-10-04 00:48:04 UTC

Permalink

Hi Alan,

Post by Alan Cox
There are some details on the Sun MMUs and similar designs. They all I
think work on the same basic principle. The low bits of the address
are passed to the row address of the main RAM (150nS or so on a
68010), and in parallel a 50nS or similar static RAM was used to look
up the high bits and then either feed them to the RAM, or generate
BERR and drop CAS so the stray write never happens if it is faulting.
Essentially the same technique every processor today uses to parallel
cache lookup and MMU.

Yep, this is very logical and straight-forward. Actually, there are
still DIP SRAMs available with pretty low access times, like 15/20/25ns,
such could be used for this LUT.
Imho, as we discussed the topic some time ago, the big PITA in such
approach is how to write (or read-back if needed) this paging LUT
without disturbing all other CPU activities.

Regards,
Nikolay

Alan Cox

2014-10-04 10:46:43 UTC

Permalink

Post by Nikolay Dimitrov
Imho, as we discussed the topic some time ago, the big PITA in such

approach is how to write (or read-back if needed) this paging LUT without
disturbing all other CPU activities

The designs I have seen bypass the MMU in supervisor mode. Even on very
modern systems MMU reloading is somewhat disruptive so from the OS side its
not a big deal. With a CPU cache that becomes even more true

I don't know how they switched the lut accesses around so you got mmio
access to the LUT however.

G. Beat

2014-10-04 17:54:18 UTC

Permalink

I have a Motorola 68030 looking for a future project.
It came out of an obsolete 1990s data compression modem for T-1 lines.

gb

yoda

2014-10-04 00:28:09 UTC

Permalink

Hi John,

Take a look at the S100-68K board derived from the Wilcox book. There is a
simple circuit to generate A0 from UDS for the S100 bus - should work on
the ECB as well.

Dave

Post by John Coffman
Sergey,
I've been thinking about a 16-bit 68000 system even before the ECB
Mini-68K CPU board was produced.
A couple of conclusions: It is easier to interface a 68020 or 68030 to
the ECB than it is to interface a 68000 or 68010. The last two do not
drive A0 -- so byte operations become complicated. The dynamic bus sizing
on the 68020/030 are very convenient.
Memory probably needs to be on a separate card. The 4MEM board has a
16Mhz limit with both the SBC-188 and Z180 Mark IV. This may be due to the
MMU on-board that card, but any discrete MMU will slow things down a
little. The integrated MMU on the 68030 becomes attractive.
My own interest is really "retro," so I still like the idea of a 68000 or
68010; however, the MMU will probably have to be on the CPU card itself.
So this tends to dictate a double-width Eurocard, like that one used on the
new 6x0x board, a board with an MMU. (VME is also double-width Eurocard,
but uses 2 connectors, rather than the ECB single connector.)
My own choice would be to stick with ECB, and to be compatible with
existing peripheral cards.
--John
Hi,
The short summer in the Pacific Northwest is coming to its end, and I
started to think about projects for the long winter.
I visited a local surplus store yesterday and picked a few MC68020 / 20
MHz processors with sockets... They were real cheap, and I couldn't resist.
:-)
So I am thinking about what should I build with these processors. Here are
- It would be nice to build a computer that could run some kind of UNIX.
Unfortunately that means the system will need to have an MMU (and the
matching MC68851 PMMU seems to be an unobtainium). Are there any UNIX-like
systems that would work without an MMU? Any other OS recommendations? OS-9
could be a good fit, but AFAIK it is not free. Or maybe I should implement
some kind of rudimentary MMU (e.g. 74LS612) or use a CPLD?
- It could be a standalone system with processor, memory, several UARTs,
block storage (most likely an IDE compatible flash card).
- Or an extendable SBC with VME or ECB bus. VME seems to be a good fit,
although I want to keep the board size small, so most likely it will be a
single connector 24-bit address/16-bit data VME variety... Here is such a
project: http://www.dutch.nl/bdj/vme/68020sys.htm
- Use 32-bit SRAM memory - four 512 KiB chips. Possibly add a connector
for a memory card for future extension (and to keep SBC small)
Thanks,
Sergey
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Kip Koon

2014-10-08 19:17:03 UTC

Permalink

Hi Guys!

What do you think about the 68012 variety. If I remember correctly it can
directly address 2GBs! Is it the only chip in the 68K series that ever did
or did some of the later 68K processors' address buses get upgraded as well?
Though I'm very interested in the 68K series of processors, I'm only now
beginning to obtain my first Mini-68000 PCB to build one. The 68020 and
68030 discussions have been very interesting also. It will be very
interesting indeed to see these come to life.

Have any of you 68K enthusiasts ever thought of putting a 680x0 VHDL core
into Grant Searle's Multicomp Microcomputer? That would interest me
greatly. James Moxham and Max Scane have been working hard on the Z80
version the Multicomp Microcomputer. A 68K version would bring the
Multicomp into the 16-bit Data Bus world not to mention running CP/M-68K or
SK*DOS! Any thought? Take care my friends!

Kip Koon

computerdoc-***@public.gmane.org

http://www.cocopedia.com/wiki/index.php/Kip_Koon

http://computerpcdoc.com/

From: n8vem-/***@public.gmane.org [mailto:n8vem-/***@public.gmane.org] On Behalf Of
John Coffman
Sent: Friday, October 03, 2014 4:44 PM
To: n8vem-/***@public.gmane.org
Subject: Re: [N8VEM: 18766] Motorola MC68020 Project Ideas

Sergey,

I've been thinking about a 16-bit 68000 system even before the ECB Mini-68K
CPU board was produced.

A couple of conclusions: It is easier to interface a 68020 or 68030 to the
ECB than it is to interface a 68000 or 68010. The last two do not drive A0
-- so byte operations become complicated. The dynamic bus sizing on the
68020/030 are very convenient.

Memory probably needs to be on a separate card. The 4MEM board has a 16Mhz
limit with both the SBC-188 and Z180 Mark IV. This may be due to the MMU
on-board that card, but any discrete MMU will slow things down a little.
The integrated MMU on the 68030 becomes attractive.

My own interest is really "retro," so I still like the idea of a 68000 or
68010; however, the MMU will probably have to be on the CPU card itself. So
this tends to dictate a double-width Eurocard, like that one used on the new
6x0x board, a board with an MMU. (VME is also double-width Eurocard, but
uses 2 connectors, rather than the ECB single connector.)

My own choice would be to stick with ECB, and to be compatible with existing
peripheral cards.

--John

On 10/03/2014 11:54 AM, Sergey wrote:

Hi,

The short summer in the Pacific Northwest is coming to its end, and I
started to think about projects for the long winter.

I visited a local surplus store yesterday and picked a few MC68020 / 20 MHz
processors with sockets... They were real cheap, and I couldn't resist. :-)

So I am thinking about what should I build with these processors. Here are
some of my ideas:
- It would be nice to build a computer that could run some kind of UNIX.
Unfortunately that means the system will need to have an MMU (and the
matching MC68851 PMMU seems to be an unobtainium). Are there any UNIX-like
systems that would work without an MMU? Any other OS recommendations? OS-9
could be a good fit, but AFAIK it is not free. Or maybe I should implement
some kind of rudimentary MMU (e.g. 74LS612) or use a CPLD?
- It could be a standalone system with processor, memory, several UARTs,
block storage (most likely an IDE compatible flash card).
- Or an extendable SBC with VME or ECB bus. VME seems to be a good fit,
although I want to keep the board size small, so most likely it will be a
single connector 24-bit address/16-bit data VME variety... Here is such a
project: http://www.dutch.nl/bdj/vme/68020sys.htm
- Use 32-bit SRAM memory - four 512 KiB chips. Possibly add a connector for
a memory card for future extension (and to keep SBC small)

Thanks,
Sergey
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Nikolay Dimitrov

2014-10-08 22:37:22 UTC

Permalink

Hi Kip,

Post by Kip Koon
Have any of you 68K enthusiasts ever thought of putting a 680x0 VHDL
core into Grant Searle's Multicomp Microcomputer?

The FPGA on Grant's board is just too small for this purpose. Here's a
project that uses much larger Altera FPGA and is designed to fit a full
m68k IP core together with some chipsets (mostly oriented towards
m68k-based Amiga and Atari machines):

http://harbaum.org/till/mist/index.shtml

The project has some nice ideas about FPGA-MCU design partitioning, I'm
sure there are people around who will be curious enough to check it out.

Regards,
Nikolay

steve shumaker

2014-10-03 23:51:17 UTC

Permalink

Post by Sergey
Hi,
The short summer in the Pacific Northwest is coming to its end, and I
started to think about projects for the long winter.
I visited a local surplus store yesterday and picked a few MC68020 /
20 MHz processors with sockets... They were real cheap, and I couldn't
resist. :-)
So I am thinking about what should I build with these processors. Here
- It would be nice to build a computer that could run some kind of
UNIX. Unfortunately that means the system will need to have an MMU
(and the matching MC68851 PMMU seems to be an unobtainium). Are there
any UNIX-like systems that would work without an MMU? Any other OS
recommendations? OS-9 could be a good fit, but AFAIK it is not free.
Or maybe I should implement some kind of rudimentary MMU (e.g.
74LS612) or use a CPLD?
- It could be a standalone system with processor, memory, several
UARTs, block storage (most likely an IDE compatible flash card).
- Or an extendable SBC with VME or ECB bus. VME seems to be a good
fit, although I want to keep the board size small, so most likely it
will be a single connector 24-bit address/16-bit data VME variety...
Here is such a project: http://www.dutch.nl/bdj/vme/68020sys.htm
- Use 32-bit SRAM memory - four 512 KiB chips. Possibly add a
connector for a memory card for future extension (and to keep SBC small)
Thanks,
Sergey
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....out of curiosity, *which* local surplus store ....

steve

Sergey

2014-10-06 17:21:31 UTC

Permalink

....out of curiosity, *which* local surplus store ....

steve

This one: http://www.surplusgizmos.com/
They have a large box with random ICs in antistatic bags... something like
$1.50 a bag. I found these MC68020 in that box... I am pretty sure I've got
all (3) of them :-)

Thanks,
Sergey

steve shumaker

2014-10-06 23:16:00 UTC

Permalink

ahhh thans! - the other Northwest lol

maybe someday....
Steve

Post by steve shumaker
....out of curiosity, *which* local surplus store ....
steve
This one: http://www.surplusgizmos.com/
They have a large box with random ICs in antistatic bags... something
like $1.50 a bag. I found these MC68020 in that box... I am pretty
sure I've got all (3) of them :-)
Thanks,
Sergey
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