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Observer ppc_mp
Observer
4,578 Views
Registered: ‎09-27-2013

Correct procedure for handling unconnected ports

Sometime when working with block designs in Vivado and making a block interface external I get more ports than I'm using. For example, the GMII interface  (via EMIO) from a Zynq PS block has the TX_ER signal ,which my HW don't use, and the tx_data bus is 8 bits long when I only use 4-bit MII on HW.

If I leave these ports unconnected (gray) they become assigned to package pins after running implemention. Does the ports connect to the package pins in the same manner as the "wanted" pins?

 

What is the correct or recommended way to handle this?

 

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4 Replies
Scholar austin
Scholar
4,543 Views
Registered: ‎02-27-2008

Re: Correct procedure for handling unconnected ports

From the constraints users guide:

 

"To trim any unused ports from the design, remove the associated constraints. The
Translate (NGDBuild) phase trims these unused pins.
In this example, there are six top-level ports. Only three (clk, A, C) are currently used.
Of the remaining three ports:
• B is kept because it has a Location (LOC) constraint.
• D is kept because it has an Input Output Standard (IOSTANDARD) constraint.
• E is trimmed because it is completely unused and unconstrained."

 

Remove any constraints that refer to that port, and it will be trimmed....

Austin Lesea
Principal Engineer
Xilinx San Jose
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Observer ppc_mp
Observer
4,524 Views
Registered: ‎09-27-2013

Re: Correct procedure for handling unconnected ports

I have now removed the ports from all the xdc files I can find in the project. They are still assigned to pins after running implementation.

 

Is the constraints users guide (UG625 ?) valid for xdc and Vivado too?

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Scholar austin
Scholar
4,519 Views
Registered: ‎02-27-2008

Re: Correct procedure for handling unconnected ports

Vivado has all new constraints, using the xdc format,

 

You will need to review the Vivado constraints....

Austin Lesea
Principal Engineer
Xilinx San Jose
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Visitor mbruno222
Visitor
1,826 Views
Registered: ‎10-03-2012

Re: Correct procedure for handling unconnected ports

In case anyone else is running into the same problem, see my solution here:

https://forums.xilinx.com/t5/Implementation/Leave-top-level-ports-unplaced/m-p/765373/highlight/true#M17855

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