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CTS and Routing

amythpai
Hello. 
I have some doubts regarding clock tree generation and routing. I am just a beginner in this field, so certain question might seem trivial:

1. Is the CTS done before the routing process or after the routing process.

2. I was trying the optimisation option in SOC encounter before routing and it inserts buffers for the two clocks which I have in the design. Can i do the optimisation after the CTS as I donot want these buffers to be added before CTS as it doesnot detect the entire path when I do the CTS. Only till the first buffer.

3.  I have a pad 
BD3CRUDQP_1V2_SF_LIN PAD_N_Clk ( .A(1'b0), .TA(1'b0), .TM(1'b0), .EN(1'b1), 
        .TEN(1'b0), .IO(Clk_PAD), .PDN(1'b1), .PUN(1'b0), .ZI(Clk) );
While doing the CTS, in the .ctstch file should i mention PAD_N_CLK/ZI in the AutoCTSRootPin option or is there any other command for IO pads?

4. I tried doing CTS after the rooting and found a lot of DRC errors when I did the verify geometry. What may be the problem? Should I now run the optimisation of the design command?

Thank you
Parents

  • 1. CTS is done before nanoRoute, but all the steps up until nanoRoute use trialRoute to do some "unofficial" routing.

    2. The opt should not be touching clock nets. The clocks are probably not defined properly in the SDC (constraints).

    3.  is the pad the root of the clock? If so, then yes you can specify that in the .ctstch. However, you probably want to specify the PAD of the IO cell, so that you get the timing through the IO cell as part of the clock tree.

    4. CTS needs to be done before nanoroute - usually the clocks are detail routed at the CTS step when all the routing resource is available. 

Reply

  • 1. CTS is done before nanoRoute, but all the steps up until nanoRoute use trialRoute to do some "unofficial" routing.

    2. The opt should not be touching clock nets. The clocks are probably not defined properly in the SDC (constraints).

    3.  is the pad the root of the clock? If so, then yes you can specify that in the .ctstch. However, you probably want to specify the PAD of the IO cell, so that you get the timing through the IO cell as part of the clock tree.

    4. CTS needs to be done before nanoroute - usually the clocks are detail routed at the CTS step when all the routing resource is available. 

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