!続・VHDLでの除算について
パス遅延65.6ns，つまり最大動作周波数が15MHzくらいになる，というのは
受け入れ難いな，とは思うけど，
ちゃんと合成可能なライブラリが用意されているのは素晴しい．

!VHDLでの除算

VHDLでは，除算で商と剰余を求めるには，それぞれ/とmodという演算子が
あることは知っていたけど，シミュレーション用であって，
合成できないと信じていた．
@kibayosさんに尋ねられたので，エラーメッセージを見てもらおうと合成してみると...
合成できるのね．使ったツールはISE 14.4．
""

HDLのソースコードは，素直に↓の通り．
singedじゃなくてunsingedでも合成できる．
 library ieee;
 use ieee.std_logic_1164.all;
 use ieee.numeric_std.all;
 
 entity arith is
   port (
     a : in signed(31 downto 0);
     b : in signed(31 downto 0);
     q : out signed(31 downto 0);
     r : out signed(31 downto 0)
     );
 end arith;
 
 architecture RTL of arith is
 
 begin  -- RTL
   process (a, b)
   begin  -- process
     q <= a / b;
     r <= a mod b;
   end process;
 end RTL;
""

対象をXC7K325T-2とした時のログからの抜粋ですが，
パス遅延は，
   Maximum combinational path delay: 65.661ns
で，合成レポートは↓のような感じ．
P&Rまで行ったときの占有スライス数は958でした．
合成したモジュールのSchematicを見ようとしたのですが，
VMWare上のWindowsで動かしているISEには荷が重いようで，断念．

 =========================================================================
 Advanced HDL Synthesis Report
 
 Macro Statistics
 # Adders/Subtractors                                   : 72
  32-bit adder                                          : 1
  32-bit adder carry in                                 : 66
  32-bit subtractor                                     : 4
  33-bit adder                                          : 1
 # Comparators                                          : 66
  32-bit comparator greater                             : 1
  32-bit comparator lessequal                           : 1
  33-bit comparator greater                             : 1
  33-bit comparator lessequal                           : 1
  34-bit comparator greater                             : 1
  34-bit comparator lessequal                           : 1
  35-bit comparator greater                             : 1
  35-bit comparator lessequal                           : 1
  36-bit comparator greater                             : 1
  36-bit comparator lessequal                           : 1
  37-bit comparator greater                             : 1
  37-bit comparator lessequal                           : 1
  38-bit comparator greater                             : 1
  38-bit comparator lessequal                           : 1
  39-bit comparator greater                             : 1
  39-bit comparator lessequal                           : 1
  40-bit comparator greater                             : 1
  40-bit comparator lessequal                           : 1
  41-bit comparator greater                             : 1
  41-bit comparator lessequal                           : 1
  42-bit comparator greater                             : 1
  42-bit comparator lessequal                           : 1
  43-bit comparator greater                             : 1
  43-bit comparator lessequal                           : 1
  44-bit comparator greater                             : 1
  44-bit comparator lessequal                           : 1
  45-bit comparator greater                             : 1
  45-bit comparator lessequal                           : 1
  46-bit comparator greater                             : 1
  46-bit comparator lessequal                           : 1
  47-bit comparator greater                             : 1
  47-bit comparator lessequal                           : 1
  48-bit comparator greater                             : 1
  48-bit comparator lessequal                           : 1
  49-bit comparator greater                             : 1
  49-bit comparator lessequal                           : 1
  50-bit comparator greater                             : 1
  50-bit comparator lessequal                           : 1
  51-bit comparator greater                             : 1
  51-bit comparator lessequal                           : 1
  52-bit comparator greater                             : 1
  52-bit comparator lessequal                           : 1
  53-bit comparator greater                             : 1
  53-bit comparator lessequal                           : 1
  54-bit comparator greater                             : 1
  54-bit comparator lessequal                           : 1
  55-bit comparator greater                             : 1
  55-bit comparator lessequal                           : 1
  56-bit comparator greater                             : 1
  56-bit comparator lessequal                           : 1
  57-bit comparator greater                             : 1
  57-bit comparator lessequal                           : 1
  58-bit comparator greater                             : 1
  58-bit comparator lessequal                           : 1
  59-bit comparator greater                             : 1
  59-bit comparator lessequal                           : 1
  60-bit comparator greater                             : 1
  60-bit comparator lessequal                           : 1
  61-bit comparator greater                             : 1
  61-bit comparator lessequal                           : 1
  62-bit comparator greater                             : 1
  62-bit comparator lessequal                           : 1
  63-bit comparator greater                             : 1
  63-bit comparator lessequal                           : 1
  64-bit comparator greater                             : 1
  64-bit comparator lessequal                           : 1
 # Multiplexers                                         : 2087
  1-bit 2-to-1 multiplexer                              : 2080
  32-bit 2-to-1 multiplexer                             : 6
  33-bit 2-to-1 multiplexer                             : 1
 # Xors                                                 : 2
  1-bit xor2                                            : 2
 
 =========================================================================