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Altera_Forum
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19 years ago

NIOS FPU Performance

Hello everybody:

I've been testing the NIOS II FPU performance and it seems to be very bad unless I'm missunderstoding something. When running the tutorial example I get the following results:

Addition: Time(Clocks) No FPU approximately 254 cycles

With FPU approximately 22 cycles

Similar results for sub and multiply instructions.

In my opinion 22 cycles is too much for an FPU. I've been searching the web and there are other processor with the FPU integrated within the pipeline which perform operations in only 1 cycle (plus latency).

Is the NIOS II FPU integrated within the pipeline?

How many cycles does it itakes to perform an operation?

The information provide by Altera doesn't talk too much about this issues.

Thanks in advance,

Luis

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    19 years ago

    --- Quote Start ---

    originally posted by luisalba@Feb 1 2007, 05:20 AM

    hello everybody:

    i've been testing the nios ii fpu performance and it seems to be very bad unless i'm missunderstoding something. when running the tutorial example i get the following results:

    addition: time(clocks) no fpu approximately 254 cycles

    with fpu approximately 22 cycles

    similar results for sub and multiply instructions.

    in my opinion 22 cycles is too much for an fpu. i've been searching the web and there are other processor with the fpu integrated within the pipeline which perform operations in only 1 cycle (plus latency).

    is the nios ii fpu integrated within the pipeline?

    how many cycles does it itakes to perform an operation?

    the information provide by altera doesn't talk too much about this issues.

    thanks in advance,

    luis

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    --- quote end ---

    --- Quote End ---

    You may have a look at www.opencores.org. There is a good FPU project. This implementation is pipelined.

    According to the doc:

    - Nr. of logic elements :

    *3468

    - fmax:

    100 MHz

    -Clock Cycles:

    Addition/Subtraction

    7

    Multiplication

    12

    Division

    35

    Square-root

    35

    Hope this helps.

    BR
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    19 years ago

    The Nios II FPU has the following calculation times (Taken from the Nios II 6.1 release notes):

    * 6 cycles

    + and - 8 cycles

    / 32 cycles

    I suspect you have overhead being accumulated in the time measurement.