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[/] [mblite/] [trunk/] [hw/] [core/] [fetch.vhd] - Rev 11

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----------------------------------------------------------------------------------------------
--
--      Input file         : fetch.vhd
--      Design name        : fetch
--      Author             : Tamar Kranenburg
--      Company            : Delft University of Technology
--                         : Faculty EEMCS, Department ME&CE
--                         : Systems and Circuits group
--
--      Description        : Instruction Fetch Stage inserts instruction into the pipeline. It
--                           uses a single port Random Access Memory component which holds
--                           the instructions. The next instruction is computed in the decode
--                           stage.
--
----------------------------------------------------------------------------------------------
 
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
 
library mblite;
use mblite.config_Pkg.all;
use mblite.core_Pkg.all;
use mblite.std_Pkg.all;
 
entity fetch is port
(
    fetch_o : out fetch_out_type;
    imem_o  : out imem_out_type;
    fetch_i : in fetch_in_type;
    rst_i   : in std_logic;
    ena_i   : in std_logic;
    clk_i   : in std_logic
);
end fetch;
 
architecture arch of fetch is
    signal r, rin   : fetch_out_type;
begin
 
    fetch_o.program_counter <= r.program_counter;
    imem_o.adr_o <= rin.program_counter;
    imem_o.ena_o <= ena_i;
 
    fetch_comb: process(fetch_i, r, rst_i)
        variable v : fetch_out_type;
    begin
        v := r;
        if rst_i = '1' then
			v.program_counter := (OTHERS => '0');
		elsif fetch_i.hazard = '1' then
            v.program_counter := r.program_counter;
        elsif fetch_i.branch = '1' then
            v.program_counter := fetch_i.branch_target;
        else
            v.program_counter := increment(r.program_counter(CFG_IMEM_SIZE - 1 downto 2)) & "00";
        end if;
        rin <= v;
    end process;
 
    fetch_seq: process(clk_i)
    begin
        if rising_edge(clk_i) then
            if rst_i = '1' then
                r.program_counter <= (others => '0');
            elsif ena_i = '1' then
                r <= rin;
            end if;
        end if;
    end process;
 
end arch;
 

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