Question: String matching with CAM?

Discussion in 'VHDL' started by Seth, Jul 31, 2003.

  1. Seth

    Seth Guest

    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?
    Seth, Jul 31, 2003
    #1
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  2. Seth

    Ray Andraka Guest

    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?


    --
    --Ray Andraka, P.E.
    President, the Andraka Consulting Group, Inc.
    401/884-7930 Fax 401/884-7950
    email
    http://www.andraka.com

    "They that give up essential liberty to obtain a little
    temporary safety deserve neither liberty nor safety."
    -Benjamin Franklin, 1759
    Ray Andraka, Aug 1, 2003
    #2
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