source: vis_dev/vis-2.1/share/vis/help/write_blifCmd.txt @ 14

  write_blif - determinize, encode and write an hnode to a blif file
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   write_blif   [-c]   [-l]   [-e  <encoding_file_name>]  [-R]  [-h]  [-v
   <verbosity_value>] [<file>]

   Encodes, determinizes, and writes all tables in the current hnode to a
   BLIF file. With the '-l' or '-c' options, or when 'write_blif' is used
   with no options, only the current hnode is written out as a blif file.
   The  '-R'  option  writes  the  entire hierarchy rooted at the current
   hnode  to the blif file, assuming all tables are deterministic and all
   variables are boolean.

   Encoding the Multi-Valued Variables:

   First,  all  multi-valued  variables  in the hnode are binary encoded.
   Each  multi-valued  variable  requires  'm'  binary  variables  in its
   encoding,  where  m = log2(n). Here 'n' is the number of values in the
   domain  of  the  multi-valued  variable.  If  variable  X has n binary
   variables  in  its encoding, these are called X0, X1, ... X. X0 is the
   least  significant  encoding  variable.  The  value  i of multi-valued
   variable X is encoded such that X0 + 2^1 * X1 + ... + 2^(n-1) * X = i.
   After  encoding,  each  table  in the hnode is written out to the blif
   file.

   Determinizing Non-Deterministic Tables:

   Non-deterministic  tables  are  determinized  by  adding  more  binary
   variables  to  a  particular variable's encoding. The variable that is
   chosen  is the one that has the smallest number of binary variables in
   its encoding. Determinization is explained by means of an example:

   Consider  the  BLIF-MV  table,  where  each  of a, b, and c can have 4
   values.  Each  multi-valued  variable  has two binary variables in its
   encoding. These are called a0, a1, b0, b1, c0 and c1.

   .model foo

   .inputs a b

   .outputs c

   .mv a, b, c 4

   .table a b ->c

   2 1 (1,2)

   (1,2) 1 3

   .end

   The  first  row  of this table represents non-determinism, since for a
   given  assignment of input values (i.e. a=2, b=1), the output can take
   on  two values (1 or 2). To determinize this row, it is split into two
   rows, each with a unique singleton output value. A new binary variable
   is  added  to the encoding of a (or b, since in this case each of them
   has  the  same  number  of  binary variables in its encoding). The new
   variable  a2  is  given  separate  values in each of the new rows. The
   resulting blif table looks like:

   .model foo

   .inputs a0 a1 a2 b0 b1

   .outputs c0 c1

   .names a0 a1 a2 b0 b1 ->c0 c1

   0 1 0 1 0 1 0 (these two rows represent

   0 1 1 1 0 0 1 row 1 of the MV table)

   1 0 - 1 0 1 1 (these two rows represent

   0 1 - 1 0 1 1 row 2 of the MV table)

   .end

   Note  that  this  table is still not deterministic, since rows 1 and 4
   have  input  minterm(s)  in  common, but the corresponding outputs are
   different.  To  resolve  this,  a  new binary variable is added to the
   encoding  for b (since b currently has the smallest encoding). For the
   conflicting  rows,  this variable b2 is assigned different values, and
   for  all  other  rows,  it is assigned a '-' value. After this change,
   rows  1 and 4 no longer have common input minterm(s). The intermediate
   table now looks like:

   .model foo

   .inputs a0 a1 a2 b0 b1 b2

   .outputs c0 c1

   .names a0 a1 a2 b0 b1 b2->c0 c1

   0 1 0 1 0 1 1 0

   0 1 1 1 0 - 0 1

   1 0 - 1 0 - 1 1

   0 1 - 1 0 0 1 1

   .end

   This  process  is  continued  until the table is determinized. In this
   example, the final blif file looks like:

   .model foo

   .inputs a0 a1 a2 a3 b0 b1 b2

   .outputs c0 c1

   .table a0 a1 a2 a3 b0 b1 b2 ->c0 c1

   0 1 0 - 1 0 1 1 0

   0 1 1 1 1 0 - 0 1

   1 0 - - 1 0 - 1 1

   0 1 - 0 1 0 0 1 1

   .end

   Blif  allows  only single output tables, so in reality the above table
   is split into two single output tables before being written out to the
   blif  file.  The  new  binary  variables  that are thus introduced are
   treated as primary inputs in the blif file.

   We  make  no  claim on the optimality of this process, just that it is
   simple.  It  may  turn  out  that  the number of new variables is much
   larger than the optimum one.

   Interfacing Between Binary and Multi-Valued Variables:

   In  order  for  the SIS-optimized version of this file to be read back
   into   VIS,  we  need  to  re-create  the  corresponding  multi-valued
   variables.  For this purpose, interface information (model name, input
   and  output  declarations  for  the hnode) is written out to a special
   encoding   file  (e.g.  foo.enc).  Additionally,  binary->multi-valued
   encoding  tables  are written to the encoding file for each PO. In the
   above  example,  the  binary->multi-valued  table for variable c looks
   like

   .table c0 c1 -> c

   0 0 0

   1 0 1

   0 1 2

   1 1 3

   and  this can be seen as a decoder of the binary variables. Similarly,
   multi-valued->binary  encoding tables are written to the encoding file
   for  each  PI.  The  multi-valued->binary  table for variable b in the
   above example is:

   .table b -> b0 b1

   0 0 0

   1 1 0

   2 0 1

   3 1 1

   and  this  can  be  seen  as an encoder of the multi-valued variables.
   Similar tables are written to the encoding file for sub-circuit inputs
   and  outputs.  Likewise,  such tables are written out for latch inputs
   and  outputs. This is needed so that the original multi-valued latches
   can  be  reinstated  while  the blif file is being read back into VIS.
   These multi-valued latch declarations are written to the encoding file
   during the write_blif process.

   The  combination  of this encoding file and the blif file results in a
   legal BLIF-MV hnode description.

   If  no file is specified, the blif file is written out to the standard
   output. If the encoding file is not specified, encoding information is
   written out to .enc.

   Options:

   The  '-R'  option  writes  the  entire hierarchy rooted at the current
   hnode   to   the  blif  file,  first  checking  that  all  tables  are
   deterministic  and  all  variables  are  boolean. Other options ('-c',
   '-l', or write_blif with no options) only write out the current hnode.
   Also,  when  the '-R' option is specified, no encoding file is written
   since none is needed.

   Command options:

   -c
          Writes only combinational part to blif file.

   -l
          Writes  out  latches,  making  latch IOs primary outputs in the
          blif file.

   -e <encoding_file_name>
          If  set,  the program writes the encoding information into this
          file.  The  default  is  the  model  name  for the current node
          extended by .enc.

   -R
          Recursively  writes  out  the  entire  hierarchy  rooted at the
          current  hnode  to  the  blif  file. In this sub-hierarchy, all
          tables must be deterministic and all variables must be boolean.
          Either of the -c, -l or -e options cannot be used together with
          this option.

   -h
          Prints the command usage.

   -v <verbosity_value>
          Specifies verbosity level, an integer less than 3.

   <file>
          name of blif file to be written, default is standard output.

          Note  that if neither the -c or the -l options are chosen, then
          latches  are  written  out,  without  making  latch IOs primary
          outputs in the blif file. Currently the files written out using
          this option cannot be read back into VIS.
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   Last updated on 20050519 10h16