Multiply and memory collision in Spartan 3

Discussion in 'VHDL' started by vcraft, May 26, 2011.

  1. vcraft

    vcraft

    Joined:
    Feb 14, 2011
    Messages:
    7
    Cheers everybody

    I am implementing some computation and some memory blocks in Xilinx Spartan 3.
    and there is following collision between memory block and multipliers:

    Code is OK, simulation and rough synthesis OK.

    But when it comes to implementation, it crahes because for each memory component Xilinx needs to allocate 1 multiply unit (for some unknown reasons, sharing some elements, whatever)

    Unfortunately I have more multiplications in the design than available. Normally it is not a problem - Xilinx allocates all hard multipliers available and the rest is created from dissipated logic.

    But in this particular case Xilinx ISE tool (fool?) first allocates absolutely all multipliers available on board for the arithmetics and then says it cannot make the memories because there are no more free multiply units left.

    Such stupid thing ...
    The question is:

    How to force Xilinx ISE to first implement the memory and then use the remaining multipliers for arithemtic action (as it should be by default).

    OR perhaps

    How to turn off the allocation of the hard multipliers for arithmetic

    OR something ?

    Is there any other way than to design these multiplying units on my own ...

    Thanks in advance
     
    vcraft, May 26, 2011
    #1
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  2. vcraft

    jeppe

    Joined:
    Mar 10, 2008
    Messages:
    348
    Location:
    Denmark
    Hi

    You can turn on/off the initialization of multipliers like this.

    1) Right click at the Synthesize -XST icon
    2) Select Process properties
    3) Select the Category - Hdl option
    4) You will find the multiplier option at the button

    your welcome
     
    jeppe, May 27, 2011
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  3. vcraft

    vcraft

    Joined:
    Feb 14, 2011
    Messages:
    7
    I am impressed.
    I have gone through enormous list of constraints, looking for something like this, but haven't found it. Whilst it was hidden just 3 clicks away.

    In desperation I have created my own multiplying unit and it helped of course.
    But is is better to use the genuine optimised design

    Thank you! I
     
    vcraft, May 30, 2011
    #3
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