Spartan 3器件上的专用乘法器路径时间随着阶段数量的增加而减少

嘿
我对Spartan 3 FPGA的乘法有一些疑问。
Spartan 3包含多达104个专用乘法器。
显然我可以选择管道这些乘法器（例如，系统生成器的“复数乘法3.1”块为我提供了这个机会，此外，所提到的块的数据表包含与乘法速度和流水线级数量相关的表格。
）。
我在18x18bit乘法器上使用17x17bit信号进行了一些测试，以查看流水线级和速度之间的关系，以找到我设计的最佳级数。
结果很奇怪。
在综合报告中，最坏情况路径时间随着阶段数量的增加而减少（对我来说听起来合乎逻辑），同时定时报告显示0个管道乘法的不合理1-2ns的最坏情况路径和1个合理的10-15ns或者
2阶段流水线。
但是，应用更多的管道并没有帮助提高速度，相反，速度随着更多阶段而降低..（所有这些应用相同的端口映射和ucf文件用于生成过程）
现在我的问题
a）是专用的乘法器，设计用于管道，还是这个选项而不是基于LUT的乘法架构？
这至少可以解释为什么在使用专用乘法器时提高流水线等级不会提高速度。
b）最好的解决方案是让System Generator自己选择阶段数量。
这里的问题是我看不到插入了多少个阶段。
因此，我无法在适当的时间内延迟与乘法器并行的路径。
我在哪里可以看到使用了多少个阶段？
顺便说一句。
我正在使用ISE 13.4和matlab 2012a
问候
baesae



以下为原文

Hey there

I do have some questions regarding multiplication on Spartan 3 FPGAs. Spartan 3 contains up to 104 dedicated multipliers. Apparently I can chose to pipeline these multipliers (I. e. the 'Complex Multiplication 3.1' block of System Generator offers me this opportunity, furthermore the datasheet of the mentioned block contains tables relating the speed of the multiplication and the amount of pipelining-stages).

I made some tests to see the relation between pipelining stages and speed using a 17x17bit signal on the 18x18bit multiplier to find the optimal amount of stages for my design. The result was strange. In the synthesis report the worst case path time decreased with increasing amount of stages (what sounds logical to me), meanwhile the timing report displayed worst case paths of unreasonable 1-2ns for the 0 piped-multiplication and reasonable 10-15ns for 1 or 2 stages pipelining. but still, applying more pipes did not help to increase speed, contrariwise the speed decreased with more stages.. (all this applying the same port map and ucf-file for generation-process)

Now my questions

a) are dedicated multipliers designed to be piped or is this option rather for the LUT based multiplication architecture? This would at least explain why enhancing grade of pipelining does not enhance speed when using dedicated multipliers.
b) The nicest solution would be to let System Generator chose the amount of stages by itself. Problem here is I cannot see how many stages were inserted. Thus I cannot delay the paths parallel to the multipliers for the appropriate time. Where can I see how many stages were used?

btw. I'm using ISE 13.4 and Matlab 2012a

Regards
baesae