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Altera_Forum's avatar
Altera_Forum
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15 years ago

Generating small rom & ram for Cyclone 3

MegaFunction wizard doesn't seem to allow using Logic Cells for small

roms & rams in Cyclone 3 as it allows in Cyclone 2. I don't want to

use a M9K for a small memory block. Anyway to get around this silly

limitation ? Am I missing something ?

TIA

Jim

2 Replies

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

    Hi,

    Using Quartus II 9.0SP2, the megawizard allows one to select LEs for RAMs but not ROMs. This seems to apply to all supported device families. Weird, I must say.

    Suggestions:

    a) hope for the best, ie, set it to "AUTO" and let the tools balance registers vs M9Ks

    b) do not use the ROM megafunction, use just plain HDL for your ROMs.
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    On second thought, I think I just made sense on what's going on.

    With RAM/ROM megafunctions, Quartus allows one to change MIF files and the quickly update the programming files without recompiling the entire design.

    However, this is only feasible when using dedicated memory blocks.

    Thus, the following restrictions are observed:

    a) ROM megafunctions (which have to have a MIF file) must use dedicated memory blocks

    b) RAM megafunctions that force the usage of LEs do not support MIF files

    So, you need to go with "b)" for any small ROMs and initialized RAMs