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Back to Simili VHDL simulator with a random.

1. As part of an evaluation to Simili simulator, I tried to compile a VHDL random module.
   The original page is page


2. The code did not compile as is from the web site. Simili did not like the way the variable is initialized. A slight code modification did it well.



1. ...
   
2. architecture Behavioral of random is
   
4.   --Pini
   
5.   constant temp_c : std_logic_vector(width-2 downto 0):=
   
6.   (others => '0');
   
8. begin
   
9.   process(clk)
   
11.     variable rand_temp : std_logic_vector(width-1 downto 0):=
    
12.     '1' & temp_c;
    
13.   --Pini
    
14.   --(width-1 => '1',others => '0');
    
16.     variable temp : std_logic := '0';
    
17.     begin
    
18.     if(rising_edge(clk)) then
    
19.       temp := rand_temp(width-1) xor rand_temp(width-2);
    
20. ...
    


3. The modified code can be downloaded from: code




4. In another project, using simili, I needed to work on a flash model from FMF. During the debug simili proved to be better than GHDL:
   
   1. While GHDL crashes on Segmentation fault, simili reported an invalid parameter used in vital function:
      VitalPathDelay01 ...
      --Commented out by Pini
      --IgnoreDefaultDelay => TRUE,
      GHDL also crashed (segmentation fault) also on a generic, which was initialized with the following string "*".
      I re-write the code to the following:
      InstancePath :STRING := "kuku";
      Another option, which proved excellent in debug, is
      --ttace-processes.
      It printed the offending process, which first removed (memory pre-load) and later fixed.
   
   
   2. Next was much more difficult to debug and fix. The FMF model used some arrays of 0 to 3. The index, which was used is an integer with range starting with -1. This caused also vhdle simulator to crash, but it did give a clue that an access of -1 to range of 0 to 3 is not allowed. Although not giving the line number, it was enough to debug. I created a function to convert negative numbers to 0 and used it instead:
      
      
      1. function f_to_pos (n : integer) return integer is
         
      2.   variable r : integer;
         
      3. variable my_line : line;
         
      4. begin
         
      5.   if( n < 0) then
         
      6.     write(my_line, string'("f_to_pos "));
         
      7.     write(my_line, n);
         
      8.     write(my_line, string'(" at "));
         
      9.     write(my_line, now);
         
      10.     writeline(output, my_line);
          
      11.     r := 0;
          
      12.   else
          
      13.     r := n;
          
      14.   end if;
          
      15.   return r;
          
      16. end f_to_pos;
          
   
   




5. The following shows a script to use vhdle (simulation script):
   
   1. #!/bin/bash
      
   2. 
      
   4. #-p no timing display to speed simulation
      
   5. #presently limit the simulation from running too long
      
   7. vhdle -nostderr -breakon error -do a.do -p -t 50us TB | tee vhdle.log
      
   8. if [ -e "simili.lst" ] ; then
      
   9.   ~/bin/lst2vcd simili.lst simili.vcd
      
   10.   if [ -e "simili.vcd.gz" ] ; then
       
   11.     rm -f simili.vcd.gz
       
   12.     gzip simili.vcd
       
   13.   fi
       
   14. fi
       

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