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Interfacing SDRAM DIMM module to DM642 over EMIF

Started by Gautham March 16, 2006
Hello
We've successfully built a board based on DM642 and we've interfaced an SDRAM
DIMM module to DM642 over EMIF (MTYPE: 64 bit SDRAM). Has anyone tried this
before. I'd like to know if there's any performance hit in using SDRAM DIMM
modules versus using a standard SDRAM chips. If yes, how much.

We're running DM642 at 600 MHz & SDRAM is configured at 100 MHz.

Thanx & regards
Gautham
	
Hello Gautham,

--- Gautham <gautham@gaut...> wrote:

> Hello
> We've successfully built a board based on DM642 and
> we've interfaced an SDRAM
> DIMM module to DM642 over EMIF (MTYPE: 64 bit
> SDRAM). Has anyone tried this
> before. I'd like to know if there's any performance
> hit in using SDRAM DIMM
> modules versus using a standard SDRAM chips. If yes,
> how much.
I haven't tried this but...
The DM642 does not have very 'strong' drivers on the
EMIF [as compared to 'bus drivers'].  Using DIMMs
successfully requires three basic things -
layout, layout, layout.  [Of course it would be much
easier if you had access to some high end simulation
tools].
1. keep the paths as short as possible
2. use the smallest series termination resistors that
you can find
3. using very rigorous testing, determine the max mem
system speed [empirically].  This can be done
effectively by using a programmable clock source to
increase the granularity of EMIF timing. Once you
think that you have it, elevate the temperature
slightly and test, test, test to verify that you have
enough margin.  Testing on DSPs from multiple lots
should be done if this is going to be productized.  I
will take a wild *guess* and say that you will end up
around 83-87 Mhz.

Also, I do not have any data on DIMMs, but you might
want to do some leg work on them regarding bus
loading.  For example, I have noticed that some
vendors use different geometry parts to get to the
same capacity - if so, the ones that use 'fewer and
wider' parts will load the address lines much less.
	mikedunn

> 
> We're running DM642 at 600 MHz & SDRAM is configured
> at 100 MHz.
> 
> Thanx & regards
> Gautham
> 
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