Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

onchip RAM resource usage

Hi all

I'm using a cyclone III EP3C40 device which boasts 126 M9K blocks for over 1Mbit onchip RAM.

I understand that 'real' memory bits are 8/9, so I have almost exactly 1Mbit.

My former design used 618472 memory bits and fitter report correctly shows 53% RAM is used.

So I increased the onchip RAM used in sopc builder, 8kbytes more: it should still fit in my device.

But Quartus answer is not!

When Quartus processes the design, it tells me it can't fit in the device because I'm using 102% of available memory.

Why?

2 Replies

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

    It depends how effeciently you are using the memory. each M9k holds 9kbits, and can only be used by 1 thing. If you have something in the design somewhere that doesnt use the memories to their max potential (like I suspenct you have) then you run into the situation you have.

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

    Thank you for your answer, Tricky

    You are right. I explored the fitter report and found out:

    Total memory bits: 618472 ot 1161216 (53%)

    M9Ks: 122 of 127 (97%)

    These are the ip modules using M9Ks in my design:

    - Nios II/f with cache

    - clock crossing bridge

    - 4 onchip memory

    - 2 tse mac

    - 2 sgdma

    - epcs and jtag controllers

    If I understand correctly what you said, even if Quartus reports a device utilizing only 40 memory bits, actually it requires a whole M9K block, then 8kbits !

    I discovered tse and sgdma modules contain plenty of such devices.

    Can I overcome this situation?

    I believe I once saw somewhere an option forcing synthesis of memory into registers rather than M9K but now I can't find it any more. Is this possible and safe?

    Thank you

    Cris