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Altera_Forum
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12 years ago

block ram area equivalent in logic elements , Cyclone iv

Hi,

I have several designs synthesized on cyclone iv fpga and all of them use only 2 resources : Logic elements and Block Rams (M9k). I want to compare the area consumption of the designs , but since each of them has different number of LE s and BRAM s I don't have a common unit of comparison. Would it make sense to find out the area equivalence of BRAMs in terms of LE s so that we have all the resources in terms of LE s and it would be possible to do a area comparison?

I wanted to know how many LE s would make up a BRAM. So

1) First I synthesised only a simple dual port memory. So the resource used was only 1 BRAM (M9K). No LE s are used.

2)Next I turned off the "auto RAM replacement" option so that the entire design is implemented using LEs. 9,939 / 109,424 ( 9 % ) - So many LE s were used up.

so 1 bram is apprx equal to 9,939 LE s. Does this make any sense or trying to express brams in terms of LE s doesn't make sense at all?

Thanks

5 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    For the present example, the comparison doesn't make much sense. Nobody would replace a dual port memory by registers, except as a mistake. It's more interesting if register banks are replaced by small sclices of block memory. In this cases, RAM blocks are often only partly populated but can still save a lot of overall FPGA resources. Due to this partial utilization, calculating LE equivalents misses the point.

  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    The synthesisor will also auto generate code into syncrams without you realising, or pack common logic together that you didnt realise was common. Shift registers are a common example. You can stop the synthesisor doing this via settings or instance assignments in the qpf, but usually this may only be neccesary for tight timing requirements.

  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    Thanks guys...

    I appreciate your replies. So is there any other way I can measure the area of the design? I was just trying to replace RAM s by LE s so that I have a common unit for measurement. Now area = no. of LEs + no. of BRAM s . How else can I compare area of my designs ? Kindly suggest me if yo have any ideas...
  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    Why do you want to? Some designs use up a lot of logic, some a lot of memory and some a lot of multipliers. If you migrate to a different family these numbers may change because of differences in architecture. Converting everything to LEs is meaningless (why would I use LEs when I have memories/DSPs available).

    You just list you project in N LEs, memories and DSP blocks, and you can carry it accross the family. The compiler will give you a % total used for each.