06-22-2009 09:41 AM
I am currently doing initial analysis on a design. I am researching different FPGA´s regarding the required resources to implement different features. I cannot find a method of relating the number of LUT´s used by a design and translating this into Logic Cells for the virtex and spartan range.
Could you please, if possible, provide me with a good estimate for each of these families? Also if possible is it possible to use convert from logic cells in Xilinx to Logic elements from altera . Are there factors that can be used between the respective families?
Basically I am looking for a general approximation of how to interchange between both LUT´s and logic elements and between logic elements and logic cells
Thank you very much for your time,
06-22-2009 11:20 AM
It is possible to do some math and compare Xilinx and Altera logic utilization. But in my experience it's not going to be accurate because there are too many factors that should be taken into consideration.
I'd recommend taking an open source design (for exampel from opencores.org) similar to yours and synthesizing it for different FPGAs.
06-25-2009 03:59 AM
I find that number of (FFs) registers in the design generally provides a better comparison between utilizations in different families.
Obviously there are some cases, such as very high speed, or logic intensive functions where this does not work, but for 95% of the cases it is OK.
Utilization is not the only factor to consider. Feature size has a major effect on power consumption and speed. Also packaging may affect your choice.
Hope this helps.
06-25-2009 04:32 AM
short answer: Forget it.
Long answer: Look at comp.arch.fpga and search for "gate equivalent" or "gate count". You will find many threads on that topic with detailed discussions.
Have a nice synthesis
06-26-2009 11:59 AM
I agree with Peter about the flip-flops.
When comparing FPGAs from different families / companies, I look at the number of flip-flops and the amount of block RAM to get an idea of how beefy the FPGA is. Next I look at the amount of multipliers available, especially if I'm doing DSP work. I also consider the other features I might want (embedded processor, ethernet MAC, etc).