Floorplanning with only usage estimates. Is it possible?

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I posted the jist of this on the Xilinx forums, but thought I might get
a quicker response through here...

I recently joined a large company, and my first assignment while
familiarizing myself with our imaging algorithm entails drawing a very
rough floorplan of a design that ultimately will consist 3 modules of
code (code will also be designed by two other companies). The PCB will
then be re-laid out around the FPGA (definitely a board spin at this

I have only received projected estimates on resource usage from the two
other companies. I could probably convince them to shoot over more
info, but I am certain they aren't close to finished with the coding.
My team's code should eat approx. 30% of the resources on a Virtex-II
XC2V-6000. I can easily obtain the HDL for this section.

To be frank, it's been a while since I worked with FPGAs and from
toying around with ISE, I feel like I can only manipulate a floorplan
after place and route. However, this doesn't make any sense to me b/c I
feel floorplanning ideally should be performed during development.

Would someone point me in the direction floorplanning w/o code?
Any feedback is appreciated.


Re: Floorplanning with only usage estimates. Is it possible?
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By floorplanning, do you mean picking a pinout?  That should be
relatively easy - in fact, using a Virtex-II or newer device, I'll bet
there is a decent chance you could live with your current pinout(your
first paragraph seems to imply that there is an existing PCB with the
device in question on it), due to the incredible routing resources in
the Virtex-II and newer devices.  This is especially true if all three
teams do a good job of pipelining their designs.

Or... were you actually referring to making an educated guess where
individual LUTs and FFs will go?  Perhaps others would have a different
take on it, but it seems to me that this would be quite a challenge
without a high percent of the code completed, and I'm not sure what the
quality of the floorplan would really be (ie, how close it would match
what ends up going to production).

Have fun,


Re: Floorplanning with only usage estimates. Is it possible?

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Area constraints maybe? Allocate a suitably large (from best known
information) rectangle to each module, and make "the module will fit
within this allotted area, n * m slices" part of the module

If single rectangles don't work for you, then multiple rectangles may be
used, BUT the tools seem best equipped to fit one rectangle per module,
so allocate each new rectangle to one sub-module if oyu have tobreak up
a module in this way.

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Then you can try the area constraint approach with this section and see
if it fits well within the estimated area and meets timing.

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Floorplanning certainly works better after P&R, but you can draw area
constraints and save them (as an UCF) earlier in the design.

- Brian

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