[SI-LIST] Re: DDR SDRAM signal routing
- From: <Aubrey_Sparkman@xxxxxxxx>
- To: <tbiggs@xxxxxxxxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 8 Nov 2004 12:23:15 -0600
Tom,
Good point!
Or to paraphrase an earlier analogy, always drive with your lights on
the first time you go anywhere. But if you can program those
coordinates into a remote controlled vehicle (layout constraints), why
go there again?
Cheers!
Aubrey Sparkman=20
Enterprise Engineering Signal Integrity Team
Dell, Inc.=20
Aubrey_Sparkman@xxxxxxxx=20
(512) 723-3592
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Tom Biggs
Sent: Monday, November 08, 2004 12:11 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: DDR SDRAM signal routing
I'm going to play devil's advocate here just to get people thinking.
(Note that I simulate the DDR designs I've done).
Ed says "The driving force behind all this is time to market and system
reliability."
There is one other force: cost. These days we can be easily outsourced
if we are too expensive to our bosses.=3D20
How many IBM PowerPC 440GX (now AMCC's chip) designs have been done? How
many times have people simulated them and come up with design guidelines
that will work? Yes, many of these designs are different from each
other, but I would bet that many of them are EXACTLY the same. Do we
need 100 engineers to simulate the exact same thing 100 times to come up
with 100 identical sets of routing rules?=3D20
If AMCC ran lots of simulations, then came out with a set of strict
routing rules for some typical embedded 440GX applications, then someone
should be able to design a board with these rules and not have to run
simulations. Reliability should be fine if they do their job right, time
to market will be short, and cost will be low.
-tom
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Ed Sayre III
Sent: Monday, November 08, 2004 9:33 AM
To: pm_norge@xxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: DDR SDRAM signal routing
Peter,
You NEED to run simulations. I have worked on DDR SDRAMs
architectures=3D20 for many years now and every one was slightly
different. You can benefit=3D20 greatly from simulations since it
generates your skew budget, component=3D20 placement and proper
termination among other design points. If you=3D20 management tells you
that they are willing to spend the money on repeated=3D20 turns, where =
you
may or may not find the right answer, then you are wasting=3D20 your
money. Either hire a consultant with experience in the area of DDR
memory or develop your own in house expertise. There are many people
and=3D20
products available right now. The driving force behind all this is
time=3D20
to market and system reliability.
Good luck
-Ed Sayre
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NORTH EAST SYSTEMS ASSOCIATES, INC
-------------------------------------=3D20
"High Performance Engineering & Design"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Edward Sayre 3rd e-mail: esayre3@xxxxxxxx
NESA, Inc. http://www.nesa.com/
5 Lan Drive, Suite 200 Tel +1.978.392-8787 x 218
Westford, MA 01886 USA Fax +1.978.392-8686
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
At 09:32 AM 11/8/2004 +0000, you wrote:
>I have been designing different kinds of electronic products, but never
>a DDR SDRAM interface with 16 memory chips (MT46V64M8, 512Mb chip,=3D20 =
>8-bit @ 167MHz)and 2 ECC chips (same type).
>
>Between the processor (IBM PowerPC 440GX) and memory chips there =
are=3D20
>only the transmission lines and series termination resistors =
(25Ohm=3D20=20
>close to the processor). I do not have the possibility to run=3D20=20
>simulations, so it's learning by doing.
>
>The data lines are around 60-70mm and the address line around=20
>250mm!!!=3D20 long. I'm afraid I will get serious SI problems with=20
>this=3D20 configuration. I read some Appnotes but I could really use =
some
>help=3D20 from experienced SI designers. What kind of termination do I=20
>really=3D20 have to implement and what do I have to look out for?
>
>Thanks in advance
>Peter
>
>_________________________________________________________________
>Last ned MSN Messenger gratis http://www.msn.no/computing/messenger=20
>-=3D20 Den korteste veien mellom deg og dine venner
>
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