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Visitor timostehmann
Visitor
1,025 Views
Registered: ‎04-10-2014

attribute IOB "FORCE" on bi-directional pins

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Hi

 

I haven't tried IOB packing before, but I have some timing issues with an external memory bus. I am using Spartan-6. The IOB packing works for pure output pins. However, I have a bidrectional data bust. The output data (including tri-state 'Z') is clocked out onto the DATA_BUS. However, when I try to read data from DATA_BUS (e.g. data_bus_snapshot <= DATA_BUS) it generates Pack:1560 error. Ok, it makes sense, because it looks like the output of the packed FF is being used back inside the FPGA and that prevents moving the FF into the IOB. However, how else can I get hold of the data on the DATA_BUS?

 

Sorry, in advance for a probably stupid question.

 

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Xilinx Employee
Xilinx Employee
1,517 Views
Registered: ‎09-20-2012

Re: attribute IOB "FORCE" on bi-directional pins

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Hi @timostehmann

 

Rather than tapping the data at ouput of register which is getting packed in to IOB, You can tap the data at the register input. If possible you can add additional register on this path so that you loop back registered output. 

Thanks,
Deepika.
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Google your question before posting. If someone's post answers your question, mark the post as answer with "Accept as solution". If you see a particularly good and informative post, consider giving it Kudos (the star on the left)
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Xilinx Employee
Xilinx Employee
1,518 Views
Registered: ‎09-20-2012

Re: attribute IOB "FORCE" on bi-directional pins

Jump to solution

Hi @timostehmann

 

Rather than tapping the data at ouput of register which is getting packed in to IOB, You can tap the data at the register input. If possible you can add additional register on this path so that you loop back registered output. 

Thanks,
Deepika.
--------------------------------------------------------------------------------------------
Google your question before posting. If someone's post answers your question, mark the post as answer with "Accept as solution". If you see a particularly good and informative post, consider giving it Kudos (the star on the left)
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Visitor timostehmann
Visitor
934 Views
Registered: ‎04-10-2014

Re: attribute IOB "FORCE" on bi-directional pins

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Thank you vemulad! That makes sense.
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