56 lines
2.1 KiB
Plaintext
56 lines
2.1 KiB
Plaintext
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WHAT IS XNF
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Xilinx Netlist Format. This is somewhat specific to the Xilinx tool
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chain, but that is sufficiently ubiquitous that it is worth it. This
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format can be fed to place and route tools and simulators. since third
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party simulators accept XNF, the format may be useful even independent
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of Xilinx parts.
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The xnfio function is highly recommended as it optimizes use of the IO
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blocks. Without this function, the I/O blocks will probably remain
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unused.
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XNFIO FUNCTION
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The "xnfio" function transforms the netlist where the IOBs are
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concerned. The signals with PAD attributes are checked, and
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surrounding circuitry generated to conform to the logic available in
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the IOB.
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If the pad is an OPAD, the function will look for an existing buf or
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not gate connected to the PAD signal. If the gate is appropriately
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connected, the buf or not gate will be turned into an OBUF. This pulls
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the buf or inverter into the IOB, freeing a CLB and providing the
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required pin circuitry.
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If the pad is an IPAD, the function will look for a buf, and convert
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that to an IBUF. Since Xilinx IOBs cannot invert the output from an
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IBUF, NOT gates cannot be absorbed as in the OPAD case.
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/*
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* Copyright (c) 1998-1999 Stephen Williams (steve@icarus.com)
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*
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* This source code is free software; you can redistribute it
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* and/or modify it in source code form under the terms of the GNU
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* General Public License as published by the Free Software
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* Foundation; either version 2 of the License, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
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*/
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$Log: xnf.txt,v $
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Revision 1.1 1999/05/01 02:57:11 steve
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XNF target documentation.
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