Forum Discussion

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

Avalon ST to FFT megafunction variable speed

Hi everyone,

I have an implemenation of the FFT megacore, currently under the Avalon ST interface

In front of this I have a fifo

the data coming in to the system is relatively slow, possibly irregular time periods

Is it safe to use clock gating on the FFT/Avalon interface as a means to hold it back (even though this could be mid packet) while collecting more data ?

Or is it better to de-assert the valid? or both?

Hope you can point me the right way,

Regards

Pete B

4 Replies

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

    clock gating isn't really safe in FPGAs. It is better to use the valid signal and deassert it when you don't have any new data to give to the Avalon sink.

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

    --- Quote Start ---

    clock gating isn't really safe in FPGAs. It is better to use the valid signal and deassert it when you don't have any new data to give to the Avalon sink.

    --- Quote End ---

    Ok, thanks,

    so deasserting Valid mid packet doesnt do any harm though?

    Thanks again
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    13 years ago

    no it shouldn't. The sink will just wait until there is valid data again.

    Be sure to check the ready signal too. A data sample is only transferred from a source to a sink when both the valid and ready signals are asserted.