AR# 4822: 4.1i XC4000 PAR - PAR_NOGENRAMBLOCK environment variable
4.1i XC4000 PAR - PAR_NOGENRAMBLOCK environment variable
Keywords: PAR, NOGENRAMBLOCK, variable, RAM
General Description: What is the function of the PAR_NOGENRAMBLOCK environment variable?
In the M1.5 release of the Xilinx software, PAR specifically looks for distributed RAM structures in an input design, and internally builds each one up as a macro. It then places each distributed RAM macro as a whole, rather than as a collection of individual CLBs.
Typically this improves the performance of designs with large distributed RAM structures in them. However, for certain design topologies, this can sometimes decrease performance. Because of this possibility, when PAR builds these RAM structures, it also informs the user that they may disable the formation of the macros by setting a PAR_NOGENRAMBLOCK environment variable.