how will the selection of FPGA affect the utilization for a common program? (Xilinx)

[his_grace]

Hi,
I am using Xilinx ISE 9.2 for my program code. Will the number of slices used, slice registers used, LUTs, IOBs etc change if we change the FPGA device, if we use the very same program for all these devices? Am working on Virtex2p, vitex4, spartan3, spartan3e... The same program should use only same number of slices even if it is on different devices. Am I right? If not, why is it so?

 

[bking]

No, it likely will not be the same.

The different families have different internal stuctures. The number of inputs per LUT may differ between familes (Spartan3 vs Virtex2 vs Virtex4, etc.), so that number may differ depending on how you are using them. IOB's may be able to utilize registers in one family that may not exist in another. There is no real comparison between different families of parts.

 

[TrickyDicky]

Heres something that also may confuse you: two builds with exactly the same source code and exactly the same chip can have different resource usages. It can depend on other things like project settings, timing specs and fitter seed.

 

[his_grace]

Heres something that also may confuse you: two builds with exactly the same source code and exactly the same chip can have different resource usages. It can depend on other things like project settings, timing specs and fitter seed.

Ohh that is something serious I should look into.
Thanks lot