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--

--      Input file         : core_wb_adapter.vhd

--      Design name        : core_wb_adapter.vhd

--      Author             : Tamar Kranenburg

--      Company            : Delft University of Technology

--                         : Faculty EEMCS, Department ME&CE

--                         : Systems and Circuits group

--

--      Description        : Wishbone adapter for the MB-Lite microprocessor. The data output

--                           is registered for multicycle transfers. This adapter implements

--                           the synchronous Wishbone Bus protocol, Rev3B.

--

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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 core_wb_adapter is port

(

    dmem_i : out dmem_in_type;

    wb_o   : out wb_mst_out_type;

    dmem_o : in dmem_out_type;

    wb_i   : in wb_mst_in_type

);

end core_wb_adapter;

architecture arch of core_wb_adapter is

    signal r_cyc_o : std_logic;

    signal rin_cyc_o : std_logic;

    signal r_data, rin_data : std_logic_vector(CFG_DMEM_WIDTH - 1 downto 0);

    signal s_wait : std_logic;

begin

    -- Direct input-output connections

    wb_o.adr_o   <= dmem_o.adr_o;

    wb_o.sel_o   <= dmem_o.sel_o;

    wb_o.we_o    <= dmem_o.we_o;

    dmem_i.dat_i <= wb_i.dat_i;

    -- synchronous bus control connections

    wb_o.cyc_o <= r_cyc_o or wb_i.ack_i;

    wb_o.stb_o <= r_cyc_o;

    -- asynchronous core enable connection

    dmem_i.ena_i <= '0' when (dmem_o.ena_o = '1' and rin_cyc_o = '1') or s_wait = '1' else '1';

    wb_o.dat_o   <= rin_data;

    -- logic for wishbone master

    wb_adapter_comb: process(wb_i, dmem_o, r_cyc_o, r_data)

    begin

        if wb_i.rst_i = '1' then

            -- reset bus

            rin_data <= r_data;

            rin_cyc_o <= '0';

            s_wait <= '0';

        elsif r_cyc_o = '1' and wb_i.ack_i = '1' then

            -- terminate wishbone cycle

            rin_data <= r_data;

            rin_cyc_o <= '0';

            s_wait <= '0';

        elsif dmem_o.ena_o = '1' and wb_i.ack_i = '1' then

            -- wishbone bus is occuppied

            rin_data <= r_data;

            rin_cyc_o <= '1';

            s_wait <= '1';

        elsif r_cyc_o = '0' and dmem_o.ena_o = '1' and wb_i.ack_i = '0' then

            -- start wishbone cycle

            rin_data <= dmem_o.dat_o;

            rin_cyc_o <= '1';

            s_wait <= '0';

        else

            -- maintain wishbone cycle

            rin_data <= r_data;

            rin_cyc_o <= r_cyc_o;

            s_wait <= '0';

        end if;

    end process;

    wb_adapter_seq: process(wb_i.clk_i)

    begin

        if rising_edge(wb_i.clk_i) then

            r_cyc_o <= rin_cyc_o;

            r_data <= rin_data;

        end if;

    end process;

end arch;