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From: caret@pyramid.com (Neil Russell)
Message-Id: <9307040425.AA17771@sword.eng.pyramid.com>
Subject: Should we provide ISA bus support?
To: riscy@pyramid.com
Date: Sat, 3 Jul 93 21:25:13 PDT
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Sender: riscy-request@pyramid.com
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Status: RO
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In general, most people want ISA.  There are one or two people
that would rather have a simple, 'riscy' specific, cheap 8-bit bus.
Then there is the issue of how many ISA sockets to provide?


No external bus at all:

Advantages:
	*  Very cheap
Disadvantages:
	*  Make expansion rather difficult


R3000 specific high bandwidth bus (local bus?):

Advantages:
	*  Peripherals that we add later can go fast.
Disadvantages:
	*  Designing a high speed expander bus is problematical
	   (lots of wave calculations)
	*  Connectors for high speed busses are expensive.
	*  No cards available, unless we make them.


R3000 specific slow speed 8-bit bus:

Advantages:
	*  Cheap, small connectors
	*  Easy to provide for on the motherboard
	*  Simple to make cards for
Disadvantages:
	*  No cards available, unless we make them


ISA bus:

Advantages:
	*  Supports many, many peripherals
	*  Allows other options for video on the motherboard
	*  Allows other options if SCSI is not used
Disadvantages:
	*  Large connectors are not the cheapest (though given the quantities
	   those things are made in, they probably are cheap)
	*  Will could not hope to support everything ISA (such as bus-
	   mastering mode, and maybe the bus sizing stuff).
	*  Uses lots of board space



A full AT ISA bus implementation provides:
	*  8-bit or 16-bit data path
	*  Flexible throttling mechanism (automatic wait state generator)
	*  Slave and Master DMA modes
	*  Automatic 16 to 8-bit translation.
	*  8.33 MHz clock rate

Of these features, the master DMA is probably the hardest to provide
since it requires access to the main memory.  Without this, there doesn't
need to be any logic to handle an extra master DMA on the main memory
(bi-directional data buffers, bus size conversion, uni-directional
address buffers, control logic).

The 16 to 8-bit translation is a convenience for the programmer that
allows a 16 bit access to an 8-bit card; it can be programmed around.

Slave DMA can be easily attached to the 3730.  The 3730 already provides
this type of DMA.  To the software, programming a DMA would be different;
to the hardware, there is no change.

As for DMA to the 3041, the 3041 would need to take an active role in
it, like it would with any DMA.  This would be fine.

The throttling is something that could be turned to our advantage.  If
were to increase the speed of the ISA bus clock to 10 or 20 MHz, and
provide for this in the wait state generation, we could get more speed
to any future peripherals that we design while maintaining compatibility
to existing cards.  (I have not researched this; there may be a very
good reason why this won't work).

If we are really clever, we could provide a simple write buffer on the
ISA bus that would allow the CPU to continue while the write completed.

(Note:  The 16 MB memory limit is not a problem if there is no memory
	provided on the bus and there are no Master DMA cards wanting to
	access main memory.)


How many sockets to provide?


This is a question of how much board space we have and what others
think.

Personally, I'd like to see four.  Apart from being a nice round number,
most machines I've seen have eight sockets.  One is usually crippled,
because its in a bad position, or doesn't have the 16-bit part of
the socket, leaving seven.  We have SCSI, video and serial on the
motherboard, reducing the required ISA bus card count by three.  I've
made some assumptions here, biased by person opinion.


Comments?
-- 
Neil Russell		(The wizard from OZ)
Pyramid Technology			Email:  caret@pyramid.com
3860 N. First Street			Voice:  (408) 428-7302
San Jose, CA 95134-1702			  FAX:  (408) 428-8845

 
From andy@piggy.waldorf-gmbh.de  Ukn Jul  4 12:33:47 1993
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From: Andreas Busse <andy@piggy.waldorf-gmbh.de>
Date: Sun, 4 Jul 93 18:33:53 GMT
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To: riscy@pyramid.com
Subject: Re: Should we provide ISA bus support?
Sender: riscy-request@pyramid.com
Reply-To: riscy@pyramid.com
Status: RO
X-Status: 



> In general, most people want ISA.  There are one or two people
> that would rather have a simple, 'riscy' specific, cheap 8-bit bus.
> Then there is the issue of how many ISA sockets to provide?
>
>
> No external bus at all:
>
> Advantages:
>	*  Very cheap
> Disadvantages:
>	*  Make expansion rather difficult

I would say: Makes expansion impossible.

> R3000 specific high bandwidth bus (local bus?):
> 
> Advantages:
> 	*  Peripherals that we add later can go fast.
> Disadvantages:
> 	*  Designing a high speed expander bus is problematical
> 	   (lots of wave calculations)
> 	*  Connectors for high speed busses are expensive.
> 	*  No cards available, unless we make them.

Do we really want to invest the wheel once again ?
There are *so* many bus systems yet... I don't think
that we have the power and market to introduce a new
bus no matter how good and fast it is.

> R3000 specific slow speed 8-bit bus:
>
> Advantages:
> 	*  Cheap, small connectors
> 	*  Easy to provide for on the motherboard
> 	*  Simple to make cards for
> Disadvantages:
> 	*  No cards available, unless we make them

As above, plus the disadvantage that it will be slow :-)


> ISA bus:
>
> Advantages:
> 	*  Supports many, many peripherals
> 	*  Allows other options for video on the motherboard
> 	*  Allows other options if SCSI is not used
> Disadvantages:
> 	*  Large connectors are not the cheapest (though given the quantities
> 	   those things are made in, they probably are cheap)
> 	*  Will could not hope to support everything ISA (such as bus-
> 	   mastering mode, and maybe the bus sizing stuff).
> 	*  Uses lots of board space

In fact, the connectors are old-fashioned and use a
lot of boardspace. But we don't need that many slots
as a PC has, because we have most of the necessary
I/O stuff on-board. One might need two, perhaps 3 slots.
That will be sufficient for 99% of all applications.

> A full AT ISA bus implementation provides:
>	*  8-bit or 16-bit data path
>	*  Flexible throttling mechanism (automatic wait state generator)
>	*  Slave and Master DMA modes
>	*  Automatic 16 to 8-bit translation.
>	*  8.33 MHz clock rate

The discussion about DMA modes is already in progress.
Perhaps there's no need to support DMA on the ISA bus.
Comments ?

Andy

-------------------------------------------------------------------------------
Andreas Busse             | e-mail: andy@piggy.waldorf-gmbh.de (home)
Eislebenstrasse 5         |         andy@resi.waldorf-gmbh.de (office)
D-5300 Bonn 1             | Phone:  +49 (0)228-252687
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From rei2!tsprad@uunet.UU.NET  Ukn Jul  4 16:26:20 1993
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From: rei2!tsprad@uunet.UU.NET (6692)
Message-Id: <9307042014.AA16767@rei.com>
Subject: Should we provide ISA bus support?
To: riscy@pyramid.com
Date: Sun, 4 Jul 1993 15:14:58 -0500 (CDT)
In-Reply-To: <9307040721.AA15244@rei.com> from "UUCP Login" at Jul 4, 93 02:21:57 am
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Neill said:
> Subject: Should we provide ISA bus support?
> 
> No external bus at all:
> 
> Advantages:
> 	*  Very cheap
    -> Very easy to design, probably get it right the 1st time.
    -> Very little board space
> Disadvantages:
> 	*  Make expansion rather difficult
    -> One would have to go back to the 'sources' and do a new board
    layout, and have new boards made
> 
> 
> R3000 specific high bandwidth bus (local bus?):
> 
> Advantages:
> 	*  Peripherals that we add later can go fast.
> Disadvantages:
> 	*  Designing a high speed expander bus is problematical
> 	   (lots of wave calculations)
> 	*  Connectors for high speed busses are expensive.
> 	*  No cards available, unless we make them.
    -> Very difficult to design, not just the motherboard but each
    new board that you want.  No _cheap_ expansion.
> 
> 
> R3000 specific slow speed 8-bit bus:
> 
> Advantages:
> 	*  Cheap, small connectors
> 	*  Easy to provide for on the motherboard
> 	*  Simple to make cards for
> Disadvantages:
> 	*  No cards available, unless we make them
    -> Cheaper and easier than a high-speed bus, but still not
    very.
> 
> 
> ISA bus:
> 
> [...] the master DMA is probably the hardest to provide
> since it requires access to the main memory. 
The Adaptec 1542 is the only bus master I know of.  Motherboard DMA
obviates that one.
> 
> The 16 to 8-bit translation is a convenience for the programmer that
> allows a 16 bit access to an 8-bit card; it can be programmed around.
> 
> Slave DMA can be easily attached to the 3730....
> 
What do you think of some compromise that would be compatible with
some ISA-bus boards but not others?  Or is that your point?  I
already suggested the 8-bit PC/XT bus, maybe a limited 16-bit
compromise?
> 
> How many sockets to provide?
> 
> This is a question of how much board space we have and what others
> think.
> 
That's all there is to say.

-- 
Ted Spradley   Recognition International, Inc.  Opinions are mine, not theirs.
2701 E Grauwyler Rd. |Your productivity is not enhanced when you're staring
Irving TX 75061      |at that thing.  Your productivity is enhanced when
214-579-6692         |the computer is working and you're doing something else.

 
From tim@ubitrex.mb.ca  Ukn Jul  6 11:59:28 1993
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Date: Tue, 6 Jul 93 10:57:37 CDT
From: tim@ubitrex.mb.ca (Tim Braun)
Message-Id: <9307061557.AA08272@ubitrex.mb.ca>
To: riscy@pyramid.com
Subject: Re: Should we provide ISA bus support?
Sender: riscy-request@pyramid.com
Reply-To: riscy@pyramid.com
Status: RO
X-Status: 

> No external bus at all:

Expansion becomes much too difficult.  Let's put something on, even 
if it's a 0.1"x0.1" header strip with the system (or 3730 8-bit i/o) bus.

> R3000 specific high bandwidth bus (local bus?):

In my opinion, the difficulties outweight the advantages.  Put the
stuff that need high speed on the motherboard, and use a moderate-speed
i/o bus.  Simpler expansion card design would give more expansion cards.

> R3000 specific slow speed 8-bit bus:

IMHO, this is a viable option.  We could put the ethernet and scsi
options onto daughterboards, reducing cost for those who don't use them,
and only moderately increasing cost for those who do.  But I'm not
sold on it 100%.  For those interested in audio, access to the 3730
i/o buses via a header would allow simple design of a/d or d/a modules.

> ISA bus:

Will be useful, and a good marketing move.  I think a partial 
implementation would be sufficient, with about three slots (no more).  
Too many slots gives you loading and layout hassles.  Put SCSI, ethernet 
and basic i/o on the m/board, and you don't need much else.  Works really
well for Sun Microsystems.

A real cheap option is one slot, and source one of those "put the slots
in sideways" adapter boards if you want to use more than one ISA card.

We couldn't allow DMA mastering simply, because of the 24 MByte addressing
limitation of ISA.  ISA bus DMA slaves are simpler.

An option to consider is providing each slot with a different IRQ set,
to eliminate the old IRQ conflict problem with the ISA bus.  This is
feasible with a small number of ISA slots, at least for some IRQ's.
The problem is on those ISA boards that generate more than one IRQ, otherwise
all ISA interrupts from a slot could be routed to one IRQ on the 3730.
Just a thought.

EISA uses expensive chips to interface (licensing fees to Intel built
into prices).  And expensive connectors.  We could add US$100 to the
price, for capabilities not many require.  My opinion is no EISA.

________________________________________________________________
Tim Braun                          |
Ubitrex Corporation                | Voice: 204-942-2992 ext 228
1900-155 Carlton St                | FAX:   204-942-3001
Winnipeg, Manitoba, Canada R3C 3H8 | Email: tim@ubitrex.mb.ca

 
