Warning for open cell library

when i use nangate opencell library for syenthesis or1k(openrisc 1000 core), it(RC) gives a warning like this...

Warning : Found CCS construct in the cell. [LBR-408]
: Found 'CCS' construct in file 'NangateOpenCellLibrary_worst_low_ccs.lib', at line 255, column 27.
: Currently, CCS constructs are only parsed & ignored.

what's the reason?
how can i avoid this?

and also i get target slack unconstrained for the whole design..
constraints given to the design is clk : 100MHz

please do help..

you are using the liberty file which is based on CCS model which is not supported by your tool [RTL Compiler] .
Use the liberty files which are based on the NLDM models. This will solve the problem. CCS models are more accurate than NLDM.

so What is the reason for showing "Target slack unconstrained" after synthesis???
and there also shows no generated clock found for "report clocks -generated" command in RC?

rc:/> report clocks -generated
============================================================
Generated by: Encounter(R) RTL Compiler v09.10-p104_1
Generated on: Jan 25 2011 12:01:28 PM
Module: soc_top
Technology library: NangateOpenCellLibrary revision 1.0
Operating conditions: typical (balanced_tree)
Wireload mode: enclosed
Area mode: timing library
============================================================

No clocks to report


but i given a clock constraint like this..

rc:/> report clocks
============================================================
Generated by: Encounter(R) RTL Compiler v09.10-p104_1
Generated on: Jan 25 2011 12:02:19 PM
Module: soc_top
Technology library: NangateOpenCellLibrary revision 1.0
Operating conditions: typical (balanced_tree)
Wireload mode: enclosed
Area mode: timing library
============================================================


Clock Description
-----------------

Clock Clock Source No of
Name Period Rise Fall Domain Pin/Port Registers
---------------------------------------------------------------
clk 10000.0 0.0 5000.0 domain_1 0

Clock Network Latency / Setup Uncertainty
-----------------------------------------

Network Network Source Source Setup Setup
Clock Latency Latency Latency Latency Uncertainity Uncertainity
Name Rise Fall Rise Fall Rise Fall
------------------------------------------------------------------------
clk 0.0 0.0 0.0 0.0 0.0 0.0

Clock Relationship (with uncertainity & latency)
-----------------------------------------------

From To R->R R->F F->R F->F
---------------------------------------------------
clk clk 10000.0 5000.0 5000.0 10000.0



Please do reply..