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2 questions : sprams pins and gcells

tsahi

Hello friends,

  • my first question :  

In my design there are few kinds of spram (single port ram).

My question is about the pin out of these rams, they have the same pins in every metal layer from M1 to M4 (the upper layer in the specific rams). I mean that there is a duplication of the ram pins…

Why the duplication of the pins is for ? (For more convenient routing choice for the router? , and how the router know what to choose? , can the user determine which pins on which layer will be connected –"routed"? )

I understand that when running the memory compiler, the designer choose what is the mask layer ….. – How this is connected to my question?


  • my second question :


Cadence products use the term gcell - global routing cells when the tool starting the global route.
What is the GRC percentage actually means? If I have a total GRC = 0.1% - what is actually describe? How the tool  calculate this number?

 Many thanks,

Tsahi

Parents

  •  I think it's pretty common for rams or other IP to have pins on several layers. It's so the router has a choice. If routing to one pin layer would cause a DRC violation, it can pick another layer. Whether the user can choose which one the router will connect to - well, that depends if you're talking about signal routing or power routing. For power routing, you have control. For signal routing, the router will do what it thinks is best. If you really need to control it, you could edit the LEF or put a routing blockage, etc.

    The Nanoroute chapter of the Encounter User Guide has a description of gcells. Look at the section called "Checking Congestion".

     

Reply

  •  I think it's pretty common for rams or other IP to have pins on several layers. It's so the router has a choice. If routing to one pin layer would cause a DRC violation, it can pick another layer. Whether the user can choose which one the router will connect to - well, that depends if you're talking about signal routing or power routing. For power routing, you have control. For signal routing, the router will do what it thinks is best. If you really need to control it, you could edit the LEF or put a routing blockage, etc.

    The Nanoroute chapter of the Encounter User Guide has a description of gcells. Look at the section called "Checking Congestion".

     

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