Automatic LUT sharing for SRL16s is being introduced in ISE version 11.2. The following describes the behavior of the three affected device families:
Virtex-6 Default is "AUTO", other values are "AREA" and "OFF" The value can be changed with the following variable: setenv XIL_MAP_SRL_COMPRESSION AREA (Linux) SET XIL_MAP_SRL_COMPRESSION=AREA (Windows)
Spartan-6 Default is "AREA", other values are "AUTO" and "OFF" The value can be changed with the following variable: setenv XIL_MAP_SRL_COMPRESSION AUTO (Linux) SET XIL_MAP_SRL_COMPRESSION=AUTO (Windows)
Virtex-5 Default is off. When turned on, this feature is equivalent to AREA mode. The feature can be turned on with the following variable: setenv XIL_MAP_SRL_COMPRESSION 1 (Linux) SET XIL_MAP_SRL_COMPRESSION AUTO=1 (Windows) NOTE: Unset the variable to turn this feature off for Virtex-5. Do not use "0" as any value is considered to be "on".