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Altera_Forum's avatar
Altera_Forum
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8 years ago

SignalTap & Keep Attribute - how to prepare signals for SignalTap during RTL coding?

Hi All,

I'm using the keep attribute in order to prevent from the Quartus Synthesizer to optimize (rename/delete/etc) the signals, which have such attribute.

So, is it possible to select the signals for the SignalTap using the signals attributes (e.g. keep)?

What's the technique to prepare the signals for the SignalTap during RTL coding stage? Choosing the signals manually takes toooooooo muuuuuuuch time!

Thank you!

3 Replies

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

    Instead of using keep/preserve, you can tap pre-synthesis (RTL signals) as they appear in your code (set the filter appropriately in the Node Finder when you are adding signals to the Node List). Tapping pre-synthesis signals essentially preserves them through place and route.

  • GZwei's avatar
    GZwei
    Icon for New Contributor rankNew Contributor
    6 years ago

    Unfortunately, this is not entirely true as it seems. Nodes that get removed in synthesis cannot be selected in SignalTap using pre-synthesis. The signals are visible when using the option "Design Entry (all names)", but attaching SignalTap to registers that get optimized away is not possible. Neither the syn_keep attribute and the preserve attributes work. The only way to get SignalTap to attach to these registers is to combine them with a dummy logic function that is never true, and then or it to some other signal that is used. :-(

  • MRezn's avatar
    MRezn
    Icon for New Contributor rankNew Contributor
    5 years ago

    agree, all guides lie about 'keep' flag, it does not work really for many years