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Altera_Forum's avatar
Altera_Forum
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9 years ago

Addition wrong Values, DE1-SoC

Hi,

I have the De1-SoC board. I wanted to implement an adder on fpga. The data are on the DDR3 of the HPS. I get access to them with a MSGDMA, what is controlled by the HPS.

That works fine. The addition component gets it's values from MSGDMA over Avalon Streaming interface (sink and source).

I can start the transaction and I get values back but here is the problem:

I just add +1 to the input, but the output is +2 higher

Example:

0+1 = 2 ??? is this possible?

4+1 = 6 ???

Where is the mistake?

Can anyone help me?

Thanks, Jules

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    9 years ago

    If that's all your code, the mistake is to connect to the data line of the streaming interface without providing any handshake. 

    library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.numeric_std.all;
entity Addition is
generic ( Number_of_Taps : integer := 2);
	PORT ( 		
		clk 		: in std_logic;
		reset 	: in std_logic;
		
		inDATA 	:  in std_logic_vector (15 downto 0);
		outDATA	: out std_logic_vector (15 downto 0)
		);
end Addition 
architecture rtl of Addition is
begin
  outDATA <= std_logic_vector(signed(inDATA) + 1);
end architecture;
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    9 years ago

    Thank's for your answer.

    I have a Top vhdl with the avalon streaming interface. I use the following signals: valid, ready, data

    Now I found a way. I changed the Memory from the HPS DDR3 to a on chip memory. One memory is for the input, another for the outputs. Now there are the right values.

    Is there somebody who can explain me why i have wrong values with the HPS DDR3 memory?

    I am accessing it with the fpga to hps bridge. Linux has a limited memory. So I have no problem with the access.