Forum Discussion

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

Howto keep Fan-Out-Free Nets? (noprune does not work)

I tried to implement ring oscillators that can be enabled/disabled for the purpose of consuming power / producing heat ( http://www.alteraforum.com/forum/showthread.php?t=53431 ).

But their relevant part gets removed until Post-Mapping (i.e. are not in the Technology Map Viewer).

I tried numerous preserve and noprune attributes on registers that save an arbitrary ring oscillator's output signal value, but not even one gets preserved. I even connected one output to an LED port, but it still removes it.

As described in another thread "noprune" could be a solution, but it did not work for me. (thread: http://www.alteraforum.com/forum/showthread.php?t=25178 )

Of course I also set "Remove Redundant Logic Cells" to "Off" and everything that even looked like remotely being able to influence this.

Any better suggestions?

1 Reply

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

    OK I worked around this problem by actually giving them a fanout. I made a counter and and put all outputs in a big vector that the counter addresses and selects for putting out one of them to a LED-port. Not really a nice solution as it now uses much other logic (MUXes..).

    I am still happy if someone can recommend a better solution, but for now this is ok for my experiments.