Subject: 3081+3730 worth it?

From: Bill Broadley <[email-masked]>
Date: Thu, 15 Jul 1993 18:56:56 -0500 (EDT)

I was thinking the system might be better without without the 3081+3730.

Would a plain mips 3000 40 Mhz + 3010 be cheaper???

If we ditched the 3730+3081 in favor of a mips 3000+(optional)3010+custom 
logic we could have a bigger cache (say 256k) use 72 pin simms, for max 128 
(256MB?) in 8 slots, save the $130 on the limited supplies of 3730's.  

How hard would it to replace a subset of the functionality of the 3730???
Seems like the 3730 is expensive and does more then we need and limited in 
other areas (simms).  How about moving floppy+IDE+2 serial ports+parallel+game 
to ISA for $25 or with 16550's for $45.  How about if we delete video?(GASP)

I'd think that for X11 stuff an s3-928 ($250) on ISA (5 MB/sec) would be 
faster and take less cpu then the dumb frame buffer ($100+) solution currently 
being considered.  State of the art x-terminals work on 1.25 MB/sec, couldn't 
an accelerated video card do well on ISA at 4 times the speed?  Of course if 
you couldn't afford an S3-928 ($250) you could get a lesser card. 

72 pin simms while more expensive would need 4 times less sockets, and 4 times 
less simms to interleave.  2 8MB simms that allow interleaved access are much 
more attractive then 8 1MB sims, 8 4MB sims, or 4 non-interleaved 4MB x 9's.  
I think once board space and simm sockets are taken into account the price 
increase would be marginal.

Considering that the memory efficient linux+80486 easily needs 16 Mb to run 
X11 while compiling without swapping, 64 MB or greater max would be nice.
I consider 4 MBx9 simms reasonable up to 32 MB's.

The combination of a fast cpu (40 Mhz mips) with the larger risc code size plus
linux+x11 (low locality) seems like the 24k 3081 cache would be a bottle neck 
for the system, I think that 256k or more of cache could make a big difference.
Someone posted a R4000 at 50 Mhz with 16k cache was up to twice as slow as
a 33 Mhz mips 3000 with 64 k cache.

So is this feasible?  

-- 
Bill					1st>	[email-masked]
[email-masked] <2nd 	3rd> 	             [email-masked]
Linux is great.         Bike to live, live to bike.                      PGP-ok

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From: Drew Eckhardt <[email-masked]>
Date: Thu, 15 Jul 1993 18:27:27 -0600

How hard would it to replace a subset of the functionality of the 3730???
    Seems like the 3730 is expensive and does more then we need and limited in 
    other areas (simms).  How about moving floppy+IDE+2 serial ports+parallel+g
   ame 
    to ISA for $25 or with 16550's for $45.  

Serial ports without the FIFO buffers are worthless under *nix due to 
the dropped characters, so you're talking $45 on the ISA bus.  The 
FDC37c665 chip that does this (4M FDC, IDE, 2 16550's + parallel + 
game) was originally quoted at $23, a more recent number is $21.45 
canadian or $17.80 US.  That allows a lot of room for connectors
and the RS232 drivers until we're on a par with the ISA bus. 

    How about if we delete video?(GASP I think that a lot of us don't 
   )

I want the fastest interactive system I can get for a reasonable
price.  So, I'm better off with a 486-66 and local bus video 
than I am with a MIPS4400 and ISA S3 board.  I'm sure that a lot
of other people share these goals.
    
    I'd think that for X11 stuff an s3-928 ($250) on ISA (5 MB/sec) would be 
    faster and take less cpu then the dumb frame buffer ($100+) solution curren
   tly 
    being considered.  

    State of the art x-terminals work on 1.25 MB/sec couldn 't 
    an accelerated video card do well on ISA at 4 times the speed?  

I disagree.

Unless you can put the entire Xserver on the ISA graphics board,
it's not a fair comparison.  With the S3 board, you're still
moving fonts across the ISA bus everytime you bitblt a character
since the S3 board doesn't have enough memory to cache them, with
your cheap S3 board it's using DRAM so the blitter hardware, etc.
must share bandwidth with the video serializers at 45-90M/sec
(we don't have this problem with VRAM), the X terminal has a lot 
more intelligence (ie, 40Mhz R3000) and breathing room (8M of 
memory + VRAM vs. 1M total) to accelerate things.

The S3 board may relieve some of the burden of the CPU, but on a
single user workstation, I'm interested in total interactive 
performance, so I don't care if my GCC build in the background
slows down.
    
    Of course i f 

Motherboard solution, using VRAM (assuming we get VRAM control signals 
off of the MOM chip, 3700, etc) 

2 Mac-compatible 512K VRAM SIMMS  $30/ea
1 TI tlc34076 RAMDAC              $32/ea
1 NSC LM1882 Video sync generator  $8/ea

Total : $100.  Much better than $250 for an S3 board. Not much worse than
	a Tseng ET4000 (max transfer rate 6M/sec) and cheaper than a 
	local bus board of any sort.
    
    72 pin simms while more expensive would need 4 times less sockets, 

If you shop arround 36 bit wide SIMMs are about the same price as 9 bit
wide SIMMs, ie ~$25 a megabyte.
    
    and 4 ti mes less simms to interleave.  2 8MB simms that allow interleaved 
    access are mu ch more attractive then 8 1MB sims, 8 4MB sims, or 
    4 non-interleaved 4MB x 9's
   .  
    I think once board space and simm sockets are taken into account the price 
    increase would be marginal.

Agreed.  I think that the 72 pin SIMMs are probably the route to go because
of realestate and the flexibility it gives us in interleaved memory 
configurations. Some people are arguing for 9 bit wide SIMMs because you 
have to replace less when a failure occurs - but I've never seen a memory
failure where a good chip went bad, on the 50 Unix workstations I administer
(some over 5 years old), on our VAX11/785, my PC, etc.

(On PC's, I've seen instances where new chips at a given speed don't 
work at the motherboard manufacturers' recommended number of wait 
states for that speed, but I attribute this to the marginal tollerances 
allowed for in PC design where it works if it all breaks the right way,
and haven't seen any problems using chips a speed faster (ie, 70ns 
instead of 80) than that recommended) 

Without paging *PERIOD*.  In 8M of memory, startup code will get paged 
out. With the addition of the fully unified buffercache in .99.10, with 
8M of memory and a kernel configured for my system my load average stays over 
1 during builds under X and the drive blips once every few seconds so I'm 
not thrashing.

Double that should be comfortable on a RISC.

    The combination of a fast cpu (40 Mhz mips) with the larger risc code 
    size plus linux+x11 (low locality) seems like the 24k 3081 cache would 
    be a bottle neck for the system, I think that 256k or more of cache could 
    make a big difference.

1.  That's separate I/D caches, so locality is maintained better.

2.  We have interleaved memory, which minimizes the cost of a cache miss.

3.  Our goal is "reasonable performance at a reasonable price", where
	reasonable performance in a workstation generally implies interactive
	performance.  This means what the system feels like to the user, 
	ie video, disk, etc.  So, I'd rather have onboard video than a second
	level cache.

Caching : as you add more cache, you have diminishing returns.  Some one 
needs to look at the cache hit/miss rates and decide (for our purposes)
where more cache does more harm (price) than good (performance).

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From: Jerry Callen <[email-masked]>
Date: Fri, 16 Jul 93 09:40:47 EDT

From: Bill Broadley <[email-masked]>
   Date: Thu, 15 Jul 1993 18:56:56 -0500 (EDT)

AAAARRRRRGGGGHHHH!!!

A raw R3000/3010 requires several carefully timed clock inputs. One of the
BIG advantages of one of the second generation chips, like the R3051/3081
is that all the grotty clock generation is on chip, and the chip takes a
simple, single-phase clock input. I've heard that MIPS had trouble building
R3000 based systems at >25MHz; there's no way I'd try to do a 40MHz system.
Of course, some of the folks on this list may be more macho than I.

<soapbox mode on>

The only way I can believe this project might really fly is to stick with
easy to use parts and keep the design simple. Otherwise it will never get
done.

-- Jerry

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From: Bill Broadley <[email-masked]>
Date: Fri, 16 Jul 1993 14:55:30 -0500 (EDT)

> Of course, some of the folks on this list may be more macho than I.

I wasn't familiar with the design problems of the mips 3000.

How hard would it be to just replace the 3730?? So we save $130 and can
use the 36 bit simms.  I would think the 24 k cache would make the
interleaved memory even more important.

> easy to use parts and keep the design simple. Otherwise it will never get
I agree I think the ide+floppy+uarts+parallel+game should go on the ISA.

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From: Drew Eckhardt <[email-masked]>
Date: Fri, 16 Jul 1993 13:29:19 -0600

Inegrated ide+floppy+uarts+parallel+game on motherboard : 
Takes the integrated chip, two 1488's and two 1489's and 
appropriate conectors.

ISA solution : 
Full ISA requires 1.5 sets of address lines (latched and unlatched),
several slave DMA channels, bus mastering support, variable bus sizing,
etc. 

If all people are going to do with the ISA bus is stick things
that are missing on the motherboard in it, it's going to be cheaper
and easier for us to grab the appropriate address lines, chipselects, etc 
and connect them directly to the appropriate chips than it is for
us to implement a full or even partial ISA bus implementation.

As to ISA for "expansion"  - in a workstation, I need ethernet, disk,
tape, video, and serial ports.  For expansion, as long as I can add
memory and disk as they get cheaper or my vendor "upgrades"
his software, I'm happy and don't need any sort of card slots.

--------

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From: [email-masked] (Keith Rohrer)
Date: Fri, 16 Jul 1993 14:52:42 -0600 (CDT)

> us to implement a full or even partial ISA bus implementation.
That's not the question.  The question is, is it cheaper to put ISA in than
it is to put everything anyone wants or will want before the board is
obsoleted on the board?  

> his software, I'm happy and don't need any sort of card slots.
Ooh, yeah, that's it, get yourself a big old 5.25" FH drive, and a HH,
and a 3.5" HH, and a 3.5"x1", and a 2.5", and we'll program something
to knock the drive heads against the spindles to produce 44.1kHz digital
sound!  Get another set of drives and put them in another case for stereo!

Seriously, we do need a speaker port on the motherboard for joyful coming-
to-life beepings and scornful you-screwed-up-bigtime buzzings, or otherwise
just plain clues beyond "nothing happens when you turn it on", to be used
at least by the boot ROM when it does the self-check.  Sorta like
the kind of beeps you get when you have a card in the ISA bus not quite in
straight and shorting things... 

	Keith