Foundation XVHDL, F6.x: Instantiating I/O buffers causes XNFPREP error 3530
Keywords: 3530, xnfprep, bufg, ibuf, metamor
Versions: Foundation 6.x
During design implementation, the Optimize step fails. The DRC Report lists the following error:
XNFPREP: ERROR 3530 The signal 'U1_i' is illegally connected to I/O symbols as shown below:
<lists of symbol pins corresponding to I/O and internal logic>
This error may occur if I/O components were instantiated in VHDL source code. The XVHDL compiler automatically adds I/O buffers and flip-flops to all top-level entity ports. If an I/O component is instantiated, XVHDL inserts another I/O buffer in front of the instantiated component, producing an invalid netlist.
To specify a BUFG on a clock port, use the Xilinx_BUFG attribute:
attribute Xilinx_BUFG : boolean; attribute Xilinx_BUFG of CLOCK : signal is true;
To specify an XC7300 BUFFOE on an output enable port, use the following syntax:
attribute Xilinx_BUFG : boolean; attribute Xilinx_BUFG of OUTEN : signal is true; attribute property : string; attribute property of OUTEN : signal is "SCHNM=BUFFOE";
Compile the design as a Chip. XVHDL will insert the appropriate global buffer on the port instead of an IBUF.
To specify other I/O buffers, registers, or latches, compile the design as a Macro, place the symbol on a top-level schematic, and add all I/O components using the schematic editor.