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-- The Potato Processor - A simple processor for FPGAs

-- (c) Kristian Klomsten Skordal 2014 - 2015 <kristian.skordal@wafflemail.net>

-- Report bugs and issues on <http://opencores.org/project,potato,bugtracker>

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

use work.pp_types.all;

use work.pp_csr.all;

use work.pp_utilities.all;

entity pp_memory is

        port(

                clk    : in std_logic;

                reset  : in std_logic;

                stall  : in std_logic;

                -- Data memory inputs:

                dmem_read_ack  : in std_logic;

                dmem_write_ack : in std_logic;

                dmem_data_in   : in std_logic_vector(31 downto 0);

                -- Current PC value:

                pc : in std_logic_vector(31 downto 0);

                -- Destination register signals:

                rd_write_in  : in  std_logic;

                rd_write_out : out std_logic;

                rd_data_in   : in  std_logic_vector(31 downto 0);

                rd_data_out  : out std_logic_vector(31 downto 0);

                rd_addr_in   : in  register_address;

                rd_addr_out  : out register_address;

                -- Control signals:

                branch         : in  branch_type;

                mem_op_in      : in  memory_operation_type;

                mem_size_in    : in  memory_operation_size;

                mem_op_out     : out memory_operation_type;

                -- Whether the instruction should be counted:

                count_instr_in  : in  std_logic;

                count_instr_out : out std_logic;

                -- Exception signals:

                exception_in          : in std_logic;

                exception_out         : out std_logic;

                exception_context_in  : in  csr_exception_context;

                exception_context_out : out csr_exception_context;

                -- CSR signals:

                csr_addr_in   : in  csr_address;

                csr_addr_out  : out csr_address;

                csr_write_in  : in  csr_write_mode;

                csr_write_out : out csr_write_mode;

                csr_data_in   : in  std_logic_vector(31 downto 0);

                csr_data_out  : out std_logic_vector(31 downto 0)

        );

end entity pp_memory;

architecture behaviour of pp_memory is

        signal mem_op   : memory_operation_type;

        signal mem_size : memory_operation_size;

        signal rd_data : std_logic_vector(31 downto 0);

begin

        mem_op_out <= mem_op;

        pipeline_register: process(clk)

        begin

                if rising_edge(clk) then

                        if reset = '1' then

                                rd_write_out <= '0';

                                csr_write_out <= CSR_WRITE_NONE;

                                count_instr_out <= '0';

                                mem_op <= MEMOP_TYPE_NONE;

                        elsif stall = '0' then

                                mem_size <= mem_size_in;

                                rd_data <= rd_data_in;

                                rd_addr_out <= rd_addr_in;

                                if exception_in = '1' then

                                        mem_op <= MEMOP_TYPE_NONE;

                                        rd_write_out <= '0';

                                        csr_write_out <= CSR_WRITE_REPLACE;

                                        csr_addr_out <= CSR_EPC;

                                        csr_data_out <= pc;

                                        count_instr_out <= '0';

                                else

                                        mem_op <= mem_op_in;

                                        rd_write_out <= rd_write_in;

                                        csr_write_out <= csr_write_in;

                                        csr_addr_out <= csr_addr_in;

                                        csr_data_out <= csr_data_in;

                                        count_instr_out <= count_instr_in;

                                end if;

                        end if;

                end if;

        end process pipeline_register;

        update_exception_context: process(clk)

        begin

                if rising_edge(clk) then

                        if reset = '1' then

                                exception_out <= '0';

                        else

                                exception_out <= exception_in or to_std_logic(branch = BRANCH_SRET);

                                if exception_in = '1' then

                                        exception_context_out.status <= (

                                                        pim => exception_context_in.status.im,

                                                        im => exception_context_in.status.im,

                                                        pei => exception_context_in.status.ei,

                                                        ei => '0'

                                                );

                                        exception_context_out.cause <= exception_context_in.cause;

                                        exception_context_out.badvaddr <= exception_context_in.badvaddr;

                                elsif branch = BRANCH_SRET then

                                        exception_context_out.status <= (

                                                        pim => exception_context_in.status.pim,

                                                        im => exception_context_in.status.pim,

                                                        pei => exception_context_in.status.pei,

                                                        ei => exception_context_in.status.pei

                                                );

                                        exception_context_out.cause <= CSR_CAUSE_NONE;

                                        exception_context_out.badvaddr <= (others => '0');

                                else

                                        exception_context_out.status <= exception_context_in.status;

                                        exception_context_out.cause <= CSR_CAUSE_NONE;

                                        exception_context_out.badvaddr <= (others => '0');

                                end if;

                        end if;

                end if;

        end process update_exception_context;

        rd_data_mux: process(rd_data, dmem_data_in, mem_op, mem_size)

        begin

                if mem_op = MEMOP_TYPE_LOAD or mem_op = MEMOP_TYPE_LOAD_UNSIGNED then

                        case mem_size is

                                when MEMOP_SIZE_BYTE =>

                                        if mem_op = MEMOP_TYPE_LOAD_UNSIGNED then

                                                rd_data_out <= std_logic_vector(resize(unsigned(dmem_data_in(7 downto 0)), rd_data_out'length));

                                        else

                                                rd_data_out <= std_logic_vector(resize(signed(dmem_data_in(7 downto 0)), rd_data_out'length));

                                        end if;

                                when MEMOP_SIZE_HALFWORD =>

                                        if mem_op = MEMOP_TYPE_LOAD_UNSIGNED then

                                                rd_data_out <= std_logic_vector(resize(unsigned(dmem_data_in(15 downto 0)), rd_data_out'length));

                                        else

                                                rd_data_out <= std_logic_vector(resize(signed(dmem_data_in(15 downto 0)), rd_data_out'length));

                                        end if;

                                when MEMOP_SIZE_WORD =>

                                        rd_data_out <= dmem_data_in;

                        end case;

                else

                        rd_data_out <= rd_data;

                end if;

        end process rd_data_mux;

end architecture behaviour;