spfd_pdlo - Perform SPFD-based simultaneous placement and logic optimization.
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   spfd_pdlo [-D <depth>] [-h] [-n <file>] [-r] [-t <sec>] [-v <n>] [-w <file>]
   net_file arch_file place_file route_file

   This command performs SPFD-based combined logic and placement optimization
   of combinational circuits mapped to LUT-based FPGAs to improve circuit area
   and speed. The flexibilities in the circuit are represented by SPFDs. The
   following references explain in detail the theory behind SPFDs.

   S. Yamashita, H. Sawada, and A. Nagoya. A new method to express functional
   permissibilities for LUT based FPGAs and its applications. In International
   Conference on Computer Aided Design, pages 254-261, 1996.

   Subarnarekha Sinha and Robert K. Brayton. Implementation and use of SPFDs in
   optimizaing Boolean networks. In International Conference on Computer Aided
   Design, 1998.

   The  command  implements  a technique that tightly links the logic and
   placement optimization steps. The algorithm is based on simulated annealing.
   Two types of moves, directed towards global reduction in the cost function
   (total wire length), are accepted by the simulated annealing algorithm: (1)
   wire removal/replacement, and (2) swapping of a pair of blocks in the FPGA.
   Feedback from placement is valuable in making an informed choice of a target
   wire during logic optimization moves. The logic optimization steps performed
   are similar to those of spfd_pilo, except that the placement information is
   now used instead of the fanout count. More information on this technique can
   be found in :

   Balakrishna Kumthekar and Fabio Somenzi. Power and delay reduction via
   simultaneous  logic  and  placement  optimization in FPGAs. In Design,
   Automation and Test in Europe, 2000.

   The command produces a placement file which is used by VPR for routing.

   This command can be used only if VIS is linked with VPR 4.22 (Versatile
   Place and Route), the FPGA place and route tool [1]VPR, from the University
   of Toronto. Please follow the instructions provided in the release notes to
   use VPR with VIS. You can also contact kumtheka@avanticorp.com if you need
   more help.

   Before calling this command a network should be created for the design (use
   flatten_hierarchy) and MDD ids for every node in the network should be
   created (static_order -o all -n append). Dynamic variable ordering (dvo -e
   sift) can be enabled to reduce BDD sizes.

   Command options:

   -D <depth>
          A cluster is computed which includes nodes within the specified
          'depth'. The default value is 1.

   -n <file>
          File to output the optimized circuit in VPR's .net format.

   -r
          Do not reprogram LUTs if no structural changes have been performed
          with in the cluster, i.e., if no nodes or wires have been removed do
          not  change  the local implementation of LUTs even if alternate
          implementations are availabe from SPFD information. The default is to
          reprogram.

   -t <sec>
          Time in seconds allowed to complete the command. If the computation
          time goes above that limit, the process is is aborted. The default is
          no limit.

   -v <n>
          Verbosity level.

   -w <file>
          File to output final optimized circuit.

   The following is needed by VPR:

   net_file
          The description of the circuit in the .net format. Logic optimization
          uses the circuit described in .BLIF format whereas VPR needs the same
          circuit  described in .net format. VPack (which comes with VPR)
          converts a .BLIF format into a .net format.

   arch_file
          Architecture description file for FPGAs. More information can be
          found in VPR's manual.

   place_file
          File to dump placement information.

   route_file
          File to dump routing information.

          Relevant flags to be set by the set command:

        spfd_pdlo_logic_move_freq "r1 m1 r2 m2 ..."
                Perform m1 logic moves whenever the rate of acceptance during
                simulated annealing is greater than or equal to r1, and so on.
                r1, r2, r3 ... should be monotonically decreasing, else the
                results would be unpredictable. 0 <= ri <= 1.0. For example:

                set spfd_pdlo_logic_move_freq "0.8 0 0.5 5 0.2 10"

                In the above logic schedule, zero logic moves per temperature
                will be performed when the rate of acceptance is above 0.8, 5
                logic moves between 0.8 and 0.5, 10 moves between 0.5 and 0.2.
                As no value is specified for acceptance rate close to 0.0, by
                default, 1 logic move per temperature will be performed. In
                this example it will be 1 logic move between 0.2 and 0.0. The
                quotes around the schedule are necessary.

        spfd_repl_rem
                If no, the logic optimization performs only wire removal. If
                yes, both wire replacement and removal are performed.

        spfd_pdlo_timing
                If set, use timing driven method to remove or replace wires on
                the critical path. If not set, use bounding box of the wires as
                the cost function.

        spfd_pdlo_timing_nodeorwire
                Remove/replace all the wires belonging to the most critical
                net.  If not set, attempt to remove/replace only the most
                critical wire.

        spfd_pdlo_out_crit_nets_first
                Output the circuit in VPR's .net format with the nets appearing
                in the increasing order of their slack. If not set, the initial
                net order specified in the original circuit's .net file is
                used. The file is specified with -n option. This variable is
                valid only if spfd_pdlo_timing is set.

        spfd_pdlo_remap_clb_array
                During logic optimization, due to the removal of nodes in the
                network, the current size of FPGA might be bigger than it is
                necessary. In such cases, if this variable is set, the size of
                the FPGA is reduced to fit the current logic network.

          Relevant flags that are options to VPR:

          For detailed information on the following options please refer to the
          manual that accompanies VPR source distribution.

        vpr_nodisp
        vpr_fix_pins
        vpr_nx
        vpr_ny
        vpr_fast
        vpr_init_t
        vpr_alpha_t
        vpr_exit_t
        vpr_inner_num
        vpr_seet
        vpr_place_cost_exp
        vpr_place_chan_width
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          Last updated on 20100410 00h02

References

   1. http://www.eecg.toronto.edu/~vaughn/vpr/vpr.html