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Custom Clock Tree Routing

Neeraja90

Can someone fill me with details of clock tree routing with a custom clock distribution network like H -Tree, X- Tree, etc. i. e. Can we do custom routing prior to clock tree synthesis in cadence? If so which files are to be modified?

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  • Neeraja
    Custom manual clock tree !! Why ? What doesn’t the automated flow do correctly ?
    There are hooks in the system to do almost anything you need.
    Buffer types , Route preferred layers , non-default rules , extra space , shield for root, trunk and leaf levels.

    The ONLY time we have ever done custom manual routing and buffering is at the top root level.
    We used the extra thick metal layers usually reserved for the main power grid to distribute the clock root to multiple drop points. From the drop points on CTS was totally automated.
    This was an attempt to reduce the total clock tree insertion delay on an 18x18mm die, in the end it worked, but implementation / verification was very tedious.

    I would stick to the automated flow if at all possible.
    Shawn
Reply
  • Neeraja
    Custom manual clock tree !! Why ? What doesn’t the automated flow do correctly ?
    There are hooks in the system to do almost anything you need.
    Buffer types , Route preferred layers , non-default rules , extra space , shield for root, trunk and leaf levels.

    The ONLY time we have ever done custom manual routing and buffering is at the top root level.
    We used the extra thick metal layers usually reserved for the main power grid to distribute the clock root to multiple drop points. From the drop points on CTS was totally automated.
    This was an attempt to reduce the total clock tree insertion delay on an 18x18mm die, in the end it worked, but implementation / verification was very tedious.

    I would stick to the automated flow if at all possible.
    Shawn
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