How to use the avalon bus correctly?

Hi Owerty

Look at this code:

library IEEE;
use IEEE.std_logic_1164.all;
ENTITY example IS PORT (
    clk      : IN STD_LOGIC;
    nreset      : IN STD_LOGIC;
    -- Nios interface
    Nios_Cs  : IN STD_LOGIC;
    Nios_Rd  : IN STD_LOGIC;
    Nios_Wr  : IN STD_LOGIC;
    Nios_Addr    : IN STD_LOGIC_VECTOR(2 DOWNTO 0);    -- just an example
    Nios_Din    : IN STD_LOGIC_VECTOR(31 DOWNTO 0);
    Nios_Dout   : OUT STD_LOGIC_VECTOR(31 DOWNTO 0);
    -- The output from your entity
    output: OUT STD_LOGIC
);
END example;
ARCHITECTURE behavior OF example IS
-- Define some constnts to help woth addressing when the design gets bigger
CONSTANT INPUT_1_ADDR    :    STD_LOGIC_VECTOR(2 DOWNTO 0) := "000";
CONSTANT INPUT_2_ADDR    :    STD_LOGIC_VECTOR(2 DOWNTO 0) := "001";
-- I also find this constant helpful
CONSTANT ZEROS      :    STD_LOGIC_VECTOR(31 DOWNTO 0) := (OTHERS => '0');
-- Some registers to hold internal values
SIGNAL  Input1      :    STD_LOGIC;
SIGNAL  Input2      :    STD_LOGIC;
BEGIN
PROCESS(clk,nreset)
BEGIN
    IF (nreset = '0') THEN
  Input1 <= &#39;0&#39;;
  Input2 <= &#39;0&#39;;
    ELSIF (rising_edge(clk)) THEN
  IF (Nios_Cs = &#39;1&#39; AND Nios_Wr = &#39;1&#39;) THEN
      CASE Nios_Addr IS
    WHEN "000" =>
        Input1 <= Nios_Din(0);
        Input2 <= Input2;
    WHEN "001" =>
        Input1 <= Input1;
        Input2 <= Nios_Din(1);
    WHEN OTHERS =>
        Input1 <= Input1;
        Input2 <= Input2;
      END CASE;
  ELSE
      Input1 <= Input1;
      Input2 <= Input2;
  END IF;
    END IF;
END PROCESS;
Nios_Dout <= ZEROS(31 DOWNTO 1) & Input1 WHEN Nios_Cs = &#39;1&#39; AND Nios_Rd = &#39;1&#39; AND Nios_Addr = INPUT_1_ADDR ELSE
    ZEROS(31 DOWNTO 1) & Input2 WHEN Nios_Cs = &#39;1&#39; AND Nios_Rd = &#39;1&#39; AND Nios_Addr = INPUT_2_ADDR ELSE
    (OTHERS => &#39;0&#39;);
    
output <= Input1 AND Input2    
END behavior;

This code generates a peripheral with two registers. You need to add it to your SOPC builder system and assign it with an address. You'll be able to access it from sw the same way you access any other address (with IOWR and IORD commands).

Hope this helps.

Nir