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Altera_Forum
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15 years ago

Inefficient M9K RAM usage with FPOINT

Hi Folks- I'm using Cyclone III with NIOS2 and I need to include the Altera FPOINT custom instruction. My part has 66 M9K blocks. The RAM usage summary reports that FPOINT uses a total of 1084...
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Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

My most excellent Altera FAE from Arrow solved the problem. Here are his instructions:

"I put together a little design to replicate what you are seeing, and I was able to reduce the FPOINT M9K usage from 15 to 2 by changing the following setting:

Auto RAM to Logic Cell Conversion = On

To change this, go to

Assignments - Settings - Analysis & Synthesis Settings,

click the More Settings button, and scroll down to the Auto Ram to Logic Cell Conversion setting."

I tried it and it works! You pay the price in extra LEs but the tradeoff was acceptable to me. Reviewing the RAM usage summary leads me to conclude that there is a threshold at which the build tools will decide if block RAM or LEs will be used.

I wonder what that threshold is. I wonder if the threshold is configurable.

Thanks for the comments, John Speth