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sebastianro
Participant
Participant
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Registered: ‎10-22-2010

Spartan 6 clocking wizzard ip or "manually" derive a clock

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Hi,

 

I'm working on a PCIe design on Spartan6, the clock frequency is 100 MHz but I need to read the statuses of some inputs every 10 ms. I have the following question: which is the best aproach in deriving the new clock for reading the inputs: using the clock wizzard or using a counter (from 100 MHz to 100 Hz I would need quite a counter)

 

Thanks

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eteam00
Professor
Professor
3,598 Views
Registered: ‎07-21-2009

If 100MHz is the only clock used by the fabric, then use this clock to generate the timer.

  • In the scope of a Spartan-6 device, the "quite a counter" is still a tiny flea speck of logic.
  • The counter will consume very little power compared to a 2nd clock distribution network.
  • You won't have "clock domain crossing" issues to concern yourself.
  • The S-6 PLL has a minimum output frequency of 3.125MHz.  At best you would save yourself only 6 bits of counter compared to using the 100MHz clock.

-- Bob Elkind

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eteam00
Professor
Professor
3,599 Views
Registered: ‎07-21-2009

If 100MHz is the only clock used by the fabric, then use this clock to generate the timer.

  • In the scope of a Spartan-6 device, the "quite a counter" is still a tiny flea speck of logic.
  • The counter will consume very little power compared to a 2nd clock distribution network.
  • You won't have "clock domain crossing" issues to concern yourself.
  • The S-6 PLL has a minimum output frequency of 3.125MHz.  At best you would save yourself only 6 bits of counter compared to using the 100MHz clock.

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.

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bassman59
Historian
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2,869 Views
Registered: ‎02-25-2008

 


@sebastianro wrote:

Hi,

 

I'm working on a PCIe design on Spartan6, the clock frequency is 100 MHz but I need to read the statuses of some inputs every 10 ms. I have the following question: which is the best aproach in deriving the new clock for reading the inputs: using the clock wizzard or using a counter (from 100 MHz to 100 Hz I would need quite a counter)

 

Thanks


 

Bob is correct.

Additionally, I wouldn't use the clocking wizard to create the DCM/whatever instance. I'd just instantiate the primitive directly.

----------------------------Yes, I do this for a living.
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