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PicoZed SDR Software-Defined Radio Negative Slack

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Negative Slack

ags1 over 8 years ago

I have a design (an IP) which is working fine with ZC706 but the same design is giving me a negative slack problem when used with PicoZed.

Please let me know the difference between the two on functional level.

0 drozwood90 over 8 years ago

Hi there,

Which PicoZed?
We have some that use Artix fabric (PicoZed 7010,7015,7020). We also have one that uses Kintex Fabric (PicoZed 7030).

If you are moving from a ZC706 (which uses a Zynq 7045 device), you have Kintex fabric.
https://www.xilinx.com/products/boards-and-kits/ek-z7-zc706-g.html

The Kintex fabric is faster. If your constraints are not 100% solid, you can certainly see issues like this. If your constraints are 100%, the tools will adjust the timing paths in order to account for the differences in fabric speed.

This is especially true running a lot of asynchronous latching.

--Dan
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0 albertabeef over 8 years ago

If both devices have kintex fabric (ie. 7030 versus 7045), another difference may be related to speed grade:
- the ZC706 has a Zynq-7045 device with -2 speed grade (mid)
- the PicoZed 7030 has a Zynq-7030 device with -1 speed grade (slowest)
Regards,
Mario.
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0 ags1 over 8 years ago

Thanks you for the replies . I am using PicoZed SDR (Zynq 7035) .
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0 drozwood90 over 8 years ago

Hi there,

Since you seem to have such similar fabric, I would suggest you go back through your constraints. If you are marginal on one chip, there is a strong possibility that you will not be able to meet timing on the other, this is especially true if the clock tree changes as the constraints are not providing enough information to properly set the layout.

The other issue I can think, were you working in different version of Vivado? The algorithms used to meet timing can sometimes change between versions.

--Dan
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0 ags1 over 8 years ago in reply to drozwood90

Thanks for the reply Dan.
Yes I was using Vivado 2014.2 for the ZC-706 but I had to switch to Vivado 2015.2.1 for PicoZed SDR.
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