General Description: The Core Description (inside CORE Generator) states that it is possible to place the Virtex Synchronous FIFO core in either SelectRAM+ or in Distributed RAM. However, there is no option to choose which kind of RAM to implement.
解决方案
This is an error in the Core Description for the Synchronous FIFO v1_0; this version of the core only supports Distributed RAM type.
The new version (v2_0) of Synchronous FIFO that will be released with 3.1i IP Update # 3 will have an option to implement RAM using either the Distributed RAM (SRL16) or SelectRAM+(Block RAM).