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lfd111x_building_a_risc-v-cpu_core
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Add VHDL impl. equivalent to tlv version

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T. Meissner 4 years ago
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306c34abb5
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3 changed files with 241 additions and 0 deletions
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  1. +9
    -0
      vhdl/Makefile
  2. +192
    -0
      vhdl/risc_v.vhd
  3. +40
    -0
      vhdl/tb_risc_v.vhd

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vhdl/Makefile View File

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.PHONY: sim
sim: risc_v.vhd tb_risc_v.vhd
ghdl -a --std=08 risc_v.vhd tb_risc_v.vhd
ghdl -e --std=08 tb_risc_v
ghdl -r --std=08 tb_risc_v --vcd=tb_risc_v.vcd --wave=tb_risc_v.ghw
.PHONY: clean
clean:
rm tb_risc_v tb_risc_v.ghw tb_risc_v.vcd work* *.o

+ 192
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vhdl/risc_v.vhd View File

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library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
entity risc_v is
port (
reset_n_i : in std_logic;
clk_i : in std_logic
);
end entity;
architecture rtl of risc_v is
type t_slv_array is array (natural range <>) of std_logic_vector;
subtype t_reg_file is t_slv_array(0 to 31)(31 downto 0);
subtype t_imem is t_slv_array(natural range 0 to 8)(31 downto 0);
-- Test program
constant c_imem : t_imem := (
-- ADDI, x14, x0, 0
b"0000_0000_0000_0000_0000_0111_0001_0011",
-- ADDI, x12, x0, 1010
b"0000_0000_1010_0000_0000_0110_0001_0011",
-- ADDI, x13, x0, 1
b"0000_0000_0001_0000_0000_0110_1001_0011",
-- LOOP begin
-- ADD, x14, x13, x14
b"0000_0000_1110_0110_1000_0111_0011_0011",
-- ADDI, x13, x13, 1
b"0000_0000_0001_0110_1000_0110_1001_0011",
-- BLT, x13, x12, 1111111111000 (branch to LOOP begin if x13 < x12)
b"1111_1110_1100_0110_1100_1100_1110_0011",
-- ADDI, x0, x0, 1010 (Test write ignore to x0)
b"0000_0000_1010_0000_0000_0000_0001_0011",
-- ADDI, x30, x14, 111111010100
b"1111_1101_0100_0111_0000_1111_0001_0011",
-- BGE, x0, x0, 0 (Infinite loop)
b"0000_0000_0000_0000_0101_0000_0110_0011");
signal s_reg_file : t_reg_file;
signal s_instr : std_logic_vector(31 downto 0);
signal s_imm : std_logic_vector(31 downto 0);
signal s_dec_bits : std_logic_vector(10 downto 0);
signal s_src1_value : std_logic_vector(31 downto 0);
signal s_src2_value : std_logic_vector(31 downto 0);
signal s_pc : unsigned(31 downto 0);
signal s_next_pc : unsigned(31 downto 0);
signal s_br_tgt_br : unsigned(31 downto 0);
signal s_result : signed(31 downto 0);
signal s_taken_br : boolean;
signal s_is_r_instr : boolean;
signal s_is_i_instr : boolean;
signal s_is_s_instr : boolean;
signal s_is_b_instr : boolean;
signal s_is_u_instr : boolean;
signal s_is_j_instr : boolean;
signal s_rd_valid : boolean;
signal s_funct3_valid : boolean;
signal s_rs1_valid : boolean;
signal s_rs2_valid : boolean;
signal s_funct7_valid : boolean;
signal s_imm_valid : boolean;
signal s_is_beq : boolean;
signal s_is_bne : boolean;
signal s_is_blt : boolean;
signal s_is_bge : boolean;
signal s_is_bltu : boolean;
signal s_is_bgeu : boolean;
signal s_is_addi : boolean;
signal s_is_add : boolean;
alias a_opcode : std_logic_vector(6 downto 0) is s_instr(6 downto 0);
alias a_rd : std_logic_vector(4 downto 0) is s_instr(11 downto 7);
alias a_funct3 : std_logic_vector(2 downto 0) is s_instr(14 downto 12);
alias a_rs1 : std_logic_vector(4 downto 0) is s_instr(19 downto 15);
alias a_rs2 : std_logic_vector(4 downto 0) is s_instr(24 downto 20);
alias a_funct7 : std_logic_vector(6 downto 0) is s_instr(31 downto 25);
begin
-- prog counter next state logic
s_next_pc <= 32x"0" when not reset_n_i else
s_br_tgt_br when s_taken_br else
s_pc + 4;
-- prog counter register
process (clk_i) is
begin
if rising_edge(clk_i) then
s_pc <= s_next_pc;
end if;
end process;
-- Instruction memory
s_instr <= c_imem(to_integer(s_pc(31 downto 2)));
-- Decode
-- Decode instruction type
s_is_r_instr <= s_instr(6 downto 2) = "01011" or
s_instr(6 downto 2) = "01100" or
s_instr(6 downto 2) = "01110" or
s_instr(6 downto 2) = "10100";
s_is_i_instr <= std_match(s_instr(6 downto 2), "0000-") or
std_match(s_instr(6 downto 2), "001-0") or
s_instr(6 downto 2) = "11001";
s_is_s_instr <= std_match(s_instr(6 downto 2), "0100-");
s_is_b_instr <= s_instr(6 downto 2) = "11000";
s_is_u_instr <= std_match(s_instr(6 downto 2), "0-101");
s_is_j_instr <= s_instr(6 downto 2) = "11011";
-- Extract instruction fields
s_imm <= (31 downto 11 => s_instr(31),
10 downto 0 => s_instr(30 downto 20)) when s_is_i_instr else
(31 downto 11 => s_instr(31),
10 downto 5 => s_instr(30 downto 25),
4 downto 0 => s_instr(11 downto 7)) when s_is_s_instr else
(31 downto 12 => s_instr(31),
11 => s_instr(7),
10 downto 5 => s_instr(30 downto 25),
4 downto 1 => s_instr(11 downto 8),
0 => '0') when s_is_b_instr else
( 31 => s_instr(31),
30 downto 12 => s_instr(30 downto 12),
11 downto 0 => 12x"0") when s_is_u_instr else
(31 downto 20 => s_instr(31),
19 downto 12 => s_instr(19 downto 12),
11 => s_instr(20),
10 downto 1 => s_instr(30 downto 21),
0 => '0') when s_is_j_instr else
32x"0";
-- Calculate instruction fields valids
s_rd_valid <= s_is_r_instr or s_is_i_instr or s_is_u_instr or s_is_j_instr;
s_funct3_valid <= s_is_r_instr or s_is_i_instr or s_is_s_instr or s_is_b_instr;
s_rs1_valid <= s_funct3_valid;
s_rs2_valid <= s_is_r_instr or s_is_s_instr or s_is_b_instr;
s_funct7_valid <= s_is_r_instr;
s_imm_valid <= not s_is_r_instr;
-- Instruction code decoding
s_dec_bits <= (a_funct7(5), a_funct3, a_opcode);
s_is_beq <= std_match(s_dec_bits, b"-_000_1100011");
s_is_bne <= std_match(s_dec_bits, b"-_001_1100011");
s_is_blt <= std_match(s_dec_bits, b"-_100_1100011");
s_is_bge <= std_match(s_dec_bits, b"-_101_1100011");
s_is_bltu <= std_match(s_dec_bits, b"-_110_1100011");
s_is_bgeu <= std_match(s_dec_bits, b"-_111_1100011");
s_is_addi <= std_match(s_dec_bits, b"-_000_0010011");
s_is_add <= s_dec_bits = b"0_000_0110011";
-- ALU
s_result <= signed(s_src1_value) + signed(s_imm) when s_is_addi else
signed(s_src1_value) + signed(s_src2_value) when s_is_add else
32x"0";
-- Branch logic
s_taken_br <= s_src1_value = s_src2_value when s_is_beq else
s_src1_value /= s_src2_value when s_is_bne else
signed(s_src1_value) < signed(s_src2_value) when s_is_blt else
signed(s_src1_value) >= signed(s_src2_value) when s_is_bge else
unsigned(s_src1_value) < unsigned(s_src2_value) when s_is_bltu else
unsigned(s_src1_value) >= unsigned(s_src2_value) when s_is_bgeu else
false;
s_br_tgt_br <= s_pc + unsigned(s_imm);
-- Register file
process (clk_i) is
begin
if rising_edge(clk_i) then
if reset_n_i = '0' then
s_reg_file <= (others => 32x"0");
else
if s_rd_valid and a_rd /= 5x"0" then
s_reg_file(to_integer(unsigned(a_rd))) <= std_logic_vector(s_result);
end if;
end if;
end if;
end process;
s_src1_value <= s_reg_file(to_integer(unsigned(a_rs1))) when s_rs1_valid else
(others => '0');
s_src2_value <= s_reg_file(to_integer(unsigned(a_rs2))) when s_rs2_valid else
(others => '0');
end architecture rtl;

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vhdl/tb_risc_v.vhd View File

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library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
use std.env.all;
entity tb_risc_v is
end entity tb_risc_v;
architecture sim of tb_risc_v is
signal s_clk : std_logic := '1';
signal s_reset_n : std_logic := '0';
begin
s_clk <= not s_clk after 5 ns;
s_reset_n <= '1' after 20 ns;
DUT : entity work.risc_v
port map (
reset_n_i => s_reset_n,
clk_i => s_clk
);
process is
begin
wait for 380 ns;
stop(0);
end process;
end architecture sim;

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