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Question: String matching with CAM?

 
 
Seth
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      07-31-2003
Has anyone used Content Addressable Memory to perform string matching?

I don't know much of anything about CAM, but I can imagine it would be
much more flexible than hard-coding the strings I want to search for.
However, will there be a huge hit in speed? I realize they can be
read in 1 clk, but will the max speed of the FPGA take a hit?

I don't suppose there are coded examples out there?
 
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Ray Andraka
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      08-01-2003
All the CAM really is, is a soft version of the hard coded logic. What I
mean is
by using the CAM you have the capability of reloading the 'tables' used
for the
hard coded decode. In the case of the Xilinx CAM implementation, it is
basically
an SRL-16 that gets reloaded when you write the CAM. Reads are the same
as if
the SRL16 was just a LUT. If your character set reference is not
changing, then a
LUT will serve the exact same function with possibly less overhead (the
CAM needs
a full decode on the match to handle all possibilities).

Seth wrote:

> Has anyone used Content Addressable Memory to perform string matching?
>
> I don't know much of anything about CAM, but I can imagine it would be
> much more flexible than hard-coding the strings I want to search for.
> However, will there be a huge hit in speed? I realize they can be
> read in 1 clk, but will the max speed of the FPGA take a hit?
>
> I don't suppose there are coded examples out there?


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401/884-7930 Fax 401/884-7950
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