一句xilinx ise时序约束语言求解

请问这句时序约束语言怎么理解?TIMEGRP "adc_data" OFFSET = IN 1.57ns VALID 1.55ns BEFORE "adc_clk_p" RISING】1.57ns VALID 1.55ns是什么意思?

虽然不是很懂，但是搜了一下，果然是setup和hold时间定义！
搜索关键词：TIMEGRP + VALID
OFFSET_IN
The OFFSET IN constraint defines the relationship of a clock and data as they enter
the device:
OFFSET = IN 2 ns VALID 16 ns BEFORE “clk20";  
This constraint tells the tools that data will be setup at PADs 2 ns before the clk20
rising edge, and that the data will remain valid for 16 ns after it arrives.
This
constraint only applies to PADs that go to registers that are clocked by clk20, or a
derivative of clk20 (a derived constraint).

这个应该对你有帮助！
http://www.doc88.com/p-1106054638292.html

对输入信号做一个约束，意思是说在采样沿之前要准备好，具体之前多长时间是由语句中valid前面的数字确定，valid+后面的数字是说这个信号可以持续多长时间保持有效。总的来说就是建立和保持的关系。