Answers Database

MAP: CY4 Symbol Errors. FPGA Express: Reading xnf or edf netlists into project.


Record #3508

Product Family:  Software

Product Line:  Synopsys

Problem Title:
MAP: CY4 Symbol Errors. FPGA Express: Reading xnf or edf netlists into
project.



Problem Description:
Keywords: FPGA Express, Foundation Express, Import, Add, CY4, Netlist, XNF

Urgency: Standard

General Description:
Reading XNF netlists into FPGA Express is a legitimate process.  If an XNF file

is instantiated in HDL code, it can be read in and re-optimized by Express.

Unfortunately, re-optimization of XNF files can produce problems.  Certain
attributes (like RLOCs and other placement parameters) can be removed during
the import process.  In many cases this re-optimization will remove information

that is needed to properly implement the design.  The most common problem is
with carry chains.

The following is an error message from MAP that occured after re-optimization
by Express:

ERROR:x4kma:338 - CY4 symbol
   "pv_data_MULT_A1_USIGNED_COL_1__UN_SIGNED_G1_0__M0_UB2_CARRY_0_B_U1"
   (output signal=pv_data_MULT_N32X) has a CIN signal but is configured as
   carry-initiating mode ADD-G-F1.  In this mode, the CIN pin must be left
   undriven.  Please make sure that this ADD-G-F1 CY4 has not been improperly
   instantiated in the middle of a carry chain.

ERROR:x4kma:338 - CY4 symbol
   "pv_data_MULT_A1_USIGNED_COL_0__UN_SIGNED_G1_0__M0_UB2_CARRY_0_B_U1"
   (output signal=pv_data_MULT_N39O) has a CIN signal but is configured as
   carry-initiating mode ADD-G-F1.  In this mode, the CIN pin must be left
   undriven.  Please make sure that this ADD-G-F1 CY4 has not been improperly
   instantiated in the middle of a carry chain.


Solution 1:

Simply instantiate the netlist and treat it as a black box.  Do not read the
XNF netlist into Express.  Allow M1 to merge the netlists and perform any
needed optimization.

See (Xilinx Solution 2738) for black box instantiation with Express 1.2.

For the black box instantiation flow with Express 2.0 (Foundation F1.4),
consult the Application Note Supplement.



End of Record #3508