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999068709169
Explorer
Explorer
8,865 Views
Registered: ‎09-08-2009

Unconstrained FPGA input

After checking unconstrained paths report I am wondering for a source sync.input data.

  1. Would it make sense if I use "offset in" constraint for Input Pad to IODELAY2 ? (even when phase detection is enabled)
  2. Can I ignore the unconstrained path?

 

 

 

Extra info:

I have source synchronous data and clock coming to FPGA (spartan 6 100 , PlanAhead 14,6)

I am using a ISERDES2 primitive deserializer to deserialize the data.

Phase detection is already enabled  Would it make sense if I still use "offset in" constraint?

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viviany
Xilinx Employee
Xilinx Employee
8,854 Views
Registered: ‎05-14-2008

1. I guess you're referring to using OFFSET IN to constrain the path from input pad to ISERDES. Input pad to IDELAY is not a valid timing path. And the answer is no. When you use IDELAY in variable mode, you don't need to add OFFSET IN constraint. 

2. It depands. Some unconstrained paths can be ignored but some cannot. What unconstrained path do you have?

 

Vivian

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999068709169
Explorer
Explorer
8,839 Views
Registered: ‎09-08-2009

 

  1. From the differential clock input to the internal registers (which are driven by the outputs of PLL,differential clock is PLL input) 
  2. From the differential data input to the iserdes.m and iserdes_s. (Total delay is fixed for 9 different channels and 1.674ns)

 

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viviany
Xilinx Employee
Xilinx Employee
8,823 Views
Registered: ‎05-14-2008

1. From the differential clock input to the internal registers (which are driven by the outputs of PLL,differential clock is PLL input)

----AR#18392 answers this.

http://www.xilinx.com/support/answers/18392.htm

You can just ignore this kind of paths

 

2. From the differential data input to the iserdes.m and iserdes_s. (Total delay is fixed for 9 different channels and 1.674ns)

----If these are the paths from the differential data to the data input of the ISERDES and you're using IDELAY in variable mode on these paths, you can ignore them.

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如果提供的信息能解决您的问题,请标记为“接受为解决方案”。
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