FPGA基础知识29(lut as logic 资源优化)

来自：https://forums.xilinx.com/t5/7-Series-FPGA-%E5%85%B6%E4%BB%96-FPGA-%E5%99%A8%E4%BB%B6/zynq7000-020-synthesis-LUT-overflow/m-p/886425#M892

Hi,

     我在使用zynq7000 020时，使用ECC纠错算法逻辑，综合下来LUT资源所需为73580，而020中的LUT资源为53000，超出将近40%。使用Flow_AreaOptimized_high策略替换默认策略，效果甚微，请问还有没有什么别的办法？谢谢！

注册日期： ‎05-27-2018

回复： zynq7000 020 synthesis LUT overflow

Hi @andy_lvjing,

     你在implemention那一栏下面选择report utilization,看一下你设计的哪一个模块占用了大量的LUT资源，是LUT as logic还是LUT as memory占用的多，再考虑一下从哪方面优化自己的设计。

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修改时间 ‎08-31-2018 05:14 PM

Hi,

   我们主要占用的是LUT Logic，因为ECC算法中用了大量的异或单元：

修改时间 ‎09-03-2018 06:06 PM

Hi @andy_lvjing，

    先参考一下这个链接, 你的设计里面资源利用不均，算法也需要优化。

来自：https://forums.xilinx.com/t5/7-Series-FPGAs/How-can-I-utilize-Memory-LUTs-as-a-Logic-LUT/m-p/639178/highlight/true#M12418

Hi,

I am using Kintex-7 XC7K160T-2FFG676C device with Vivado 2013.4. Since I'm not able to implement my design due over resource utilization, I have attached resourse utilization report generated after synthesis.

As per synthesis utilization report, I can see only 14% utilization of LUT as Memory and logic LUT utilization exceeds 100%. So is there a way that Memory LUTs can be utilized as logic LUTs?

Thanks,

Vijay

o answer the original question...

All LUTs are able to be used as logic. Rougly 1/4 of them can also be used as memory. Looking at your numbers it says there are 101,400 slice LUTs in the FPGA. Of this, only 35,000 can be used as memory, but all can be used as logic. Your design is trying to use 107,195 as logic and 4,727 as memory - thus a total of 111,922 of the 101,400 are used.

This is WAY too much for the device. Vivado is much better than ISE at getting high LUT utilizations, but even at that you should not be targetting more than 85% utilization - you can get a bit more, but it starts getting very difficult to meet timing at higher utilizations.

You either have to choose a larger device of simplify your design so that it doesn't use as many LUTs. You may be able to do some recoding that will allow some LUT based logic to be moved to block RAMs (some state machines can) and/or DSP slices (although you are using a good number of DSPs already), but I doubt that this is going to be enough to get this to fit in your device.