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Visitor cuhrw
Visitor
7,659 Views
Registered: ‎11-03-2015

Strange behaviour using elsif

Hello,

 

I found very strange behaviour in the synthesis in Vivado 2015.03 vor the xc7a100tcsg324-1.

 

I tried to use an "elsif" statement and the result is crap.

So I changed it so an if statement which excludes the old if condition. In theory I think that should give the same result, but in the "if statement" case it works how expected and so completely different to the elsif case.

 

Is there something that I don't see at the moment, why there os this different behavior?

 

This ist the code of the process: I change the italic to the bold part (com1 to com2).

 

process(clk) -- write_screen
variable val_pos : integer range 0 to 255;
variable value : std_logic_vector(15 downto 0);
begin
   if rising_edge(clk) then
      vga_r <= "0000";   -- Black if nothing different
      vga_g <= "0000";
      vga_b <= "0000";
      if (vga_x < 512) and (vga_y < 256) then -- Oszi Screen
         if screen_buf = bufa then
            value := buf_a(vga_x);
         else
            value := buf_b(vga_x);
         end if;
         val_pos := 256 - to_integer(unsigned((not value(15)) & value(14 downto 8)));
         if val_pos = vga_y then
            vga_b <= "1111";
         end if; -- COM 2
         if (vga_y = 128) and (val_pos /= vga_y) then  -- COM 2
       --  elsif vga_y = 128 then   -- COM 1
            vga_g <= "1111";  
         end if;
      end if;
   end if;
end process;

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1 Reply
Moderator
Moderator
7,656 Views
Registered: ‎07-21-2014

Re: Strange behaviour using elsif

@cuhrw

 

Can you elaborate on the behavior? If you are validating results with testbench then share the testbench.

 

Thanks,
Anusheel
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