AR# 7161: Foundation 2.1i The PLC attribute for clbmap primitive not supported
Foundation 2.1i The PLC attribute for clbmap primitive not supported
Keywords: fndtn, clb map, PLC, PUC, P, attribute
General Description: Using the PLC attribute to lock pins on clbmaps does not work, the workaround suggested in the libraries guide does not work either.
When using the clbmap primitive for xc3000 designs it is possible to use a PLC attribute in order to lock specific signals to CLB pins. Currently this attribute is not supported and is translated to PUC where the specific signals are not locked to clb pins and it is possible for the Xilinx tools to swap these in order to ease routing congestion.
A possible workaround is suggested in the libraries guide to use the PUC attribute but to lock the pins individually using the P attribute on the clbmap pins but this does not work either. We currently have no mechanism for locking pins, but one is being considered for a future release.