The "ise_flow.bat" implementation script file provided with MIG v2.1 controllers for all Spartan-3 Generation devices sets the XIL_ROUTE_ENABLE_DATA_CAPTURE environment variable. What does this environment variable do and is it necessary?
This environment variable is set to enable a specific algorithm within the PAR router. The Spartan-3 Generation architectures require this specific template router to ensure timing. See (Xilinx Answer 25245) for further information on the router algorithm used.
This router algorithm and the environment variable are not required for Virtex-4 and Virtex-5 MIG controllers. Setting this variable in Virtex-4 and Virtex-5 controllers has no effect on the routing.
This environment variable is also required in MIG 007 controllers for the Virtex-II and Virtex-II Pro architectures.