1 ---------------------------------------------------------------------
2 -- TITLE: Memory Controller
3 -- AUTHOR: Steve Rhoads (rhoadss@yahoo.com)
4 -- DATE CREATED: 1/31/01
5 -- FILENAME: mem_ctrl.vhd
6 -- PROJECT: Plasma CPU core
7 -- COPYRIGHT: Software placed into the public domain by the author.
8 -- Software 'as is' without warranty. Author liable for nothing.
10 -- Memory controller for the Plasma CPU.
11 -- Supports Big or Little Endian mode.
12 ---------------------------------------------------------------------
14 use ieee.std_logic_1164.all;
15 use work.mlite_pack.all;
18 port(clk : in std_logic;
19 reset_in : in std_logic;
20 pause_in : in std_logic;
21 nullify_op : in std_logic;
22 address_pc : in std_logic_vector(31 downto 2);
23 opcode_out : out std_logic_vector(31 downto 0);
25 address_in : in std_logic_vector(31 downto 0);
26 mem_source : in mem_source_type;
27 data_write : in std_logic_vector(31 downto 0);
28 data_read : out std_logic_vector(31 downto 0);
29 pause_out : out std_logic;
31 address_next : out std_logic_vector(31 downto 2);
32 byte_we_next : out std_logic_vector(3 downto 0);
34 address : out std_logic_vector(31 downto 2);
35 byte_we : out std_logic_vector(3 downto 0);
36 data_w : out std_logic_vector(31 downto 0);
37 data_r : in std_logic_vector(31 downto 0));
38 end; --entity mem_ctrl
40 architecture logic of mem_ctrl is
41 --"00" = big_endian; "11" = little_endian
42 constant ENDIAN_MODE : std_logic_vector(1 downto 0) := "00";
43 signal opcode_reg : std_logic_vector(31 downto 0);
44 signal next_opcode_reg : std_logic_vector(31 downto 0);
45 signal address_reg : std_logic_vector(31 downto 2);
46 signal byte_we_reg : std_logic_vector(3 downto 0);
48 signal mem_state_reg : std_logic;
49 constant STATE_ADDR : std_logic := '0';
50 constant STATE_ACCESS : std_logic := '1';
54 mem_proc: process(clk, reset_in, pause_in, nullify_op,
55 address_pc, address_in, mem_source, data_write,
56 data_r, opcode_reg, next_opcode_reg, mem_state_reg,
57 address_reg, byte_we_reg)
58 variable address_var : std_logic_vector(31 downto 2);
59 variable data_read_var : std_logic_vector(31 downto 0);
60 variable data_write_var : std_logic_vector(31 downto 0);
61 variable opcode_next : std_logic_vector(31 downto 0);
62 variable byte_we_var : std_logic_vector(3 downto 0);
63 variable mem_state_next : std_logic;
64 variable pause_var : std_logic;
65 variable bits : std_logic_vector(1 downto 0);
67 byte_we_var := "0000";
69 data_read_var := ZERO;
70 data_write_var := ZERO;
71 mem_state_next := mem_state_reg;
72 opcode_next := opcode_reg;
76 data_read_var := data_r;
78 when MEM_READ16 | MEM_READ16S =>
79 if address_in(1) = ENDIAN_MODE(1) then
80 data_read_var(15 downto 0) := data_r(31 downto 16);
82 data_read_var(15 downto 0) := data_r(15 downto 0);
84 if mem_source = MEM_READ16 or data_read_var(15) = '0' then
85 data_read_var(31 downto 16) := ZERO(31 downto 16);
87 data_read_var(31 downto 16) := ONES(31 downto 16);
90 when MEM_READ8 | MEM_READ8S =>
91 bits := address_in(1 downto 0) xor ENDIAN_MODE;
93 when "00" => data_read_var(7 downto 0) := data_r(31 downto 24);
94 when "01" => data_read_var(7 downto 0) := data_r(23 downto 16);
95 when "10" => data_read_var(7 downto 0) := data_r(15 downto 8);
96 when others => data_read_var(7 downto 0) := data_r(7 downto 0);
98 if mem_source = MEM_READ8 or data_read_var(7) = '0' then
99 data_read_var(31 downto 8) := ZERO(31 downto 8);
101 data_read_var(31 downto 8) := ONES(31 downto 8);
105 data_write_var := data_write;
106 byte_we_var := "1111";
109 data_write_var := data_write(15 downto 0) & data_write(15 downto 0);
110 if address_in(1) = ENDIAN_MODE(1) then
111 byte_we_var := "1100";
113 byte_we_var := "0011";
117 data_write_var := data_write(7 downto 0) & data_write(7 downto 0) &
118 data_write(7 downto 0) & data_write(7 downto 0);
119 bits := address_in(1 downto 0) xor ENDIAN_MODE;
122 byte_we_var := "1000";
124 byte_we_var := "0100";
126 byte_we_var := "0010";
128 byte_we_var := "0001";
134 if mem_source = MEM_FETCH then --opcode fetch
135 address_var := address_pc;
136 opcode_next := data_r;
137 mem_state_next := STATE_ADDR;
139 if mem_state_reg = STATE_ADDR then
140 if pause_in = '0' then
141 address_var := address_in(31 downto 2);
142 mem_state_next := STATE_ACCESS;
145 address_var := address_pc;
146 byte_we_var := "0000";
149 if pause_in = '0' then
150 address_var := address_pc;
151 opcode_next := next_opcode_reg;
152 mem_state_next := STATE_ADDR;
153 byte_we_var := "0000";
155 address_var := address_in(31 downto 2);
156 byte_we_var := "0000";
161 if nullify_op = '1' and pause_in = '0' then
162 opcode_next := ZERO; --NOP after beql
165 if reset_in = '1' then
166 mem_state_reg <= STATE_ADDR;
168 next_opcode_reg <= ZERO;
169 address_reg <= ZERO(31 downto 2);
170 byte_we_reg <= "0000";
171 elsif rising_edge(clk) then
172 if pause_in = '0' then
173 address_reg <= address_var;
174 byte_we_reg <= byte_we_var;
175 mem_state_reg <= mem_state_next;
176 opcode_reg <= opcode_next;
177 if mem_state_reg = STATE_ADDR then
178 next_opcode_reg <= data_r;
183 opcode_out <= opcode_reg;
184 data_read <= data_read_var;
185 pause_out <= pause_var;
187 address_next <= address_var;
188 byte_we_next <= byte_we_var;
190 address <= address_reg;
191 byte_we <= byte_we_reg;
192 data_w <= data_write_var;
194 end process; --data_proc
196 end; --architecture logic