simulation/cpu/decoder.vhd

   1 library ieee;
   2 use ieee.std_logic_1164.all;
   3 use ieee.std_logic_arith.conv_std_logic_vector;
   4 --use ieee.std_logic_arith.all;
   5 use std.textio.all;
   6 use ieee.std_logic_textio.all;
   7 use ieee.std_logic_unsigned.conv_integer;
   8
   9 entity decoder is
  10     generic (dsize : integer := 8);
  11     port (  set_clk         : in std_logic;
  12             trig_clk        : in std_logic;
  13             res_n           : in std_logic;
  14             irq_n           : in std_logic;
  15             nmi_n           : in std_logic;
  16             rdy             : in std_logic;
  17             instruction     : in std_logic_vector (dsize - 1 downto 0);
  18             status_reg      : in std_logic_vector (dsize - 1 downto 0);
  19             pcl_d_i_n       : out std_logic;
  20             pcl_d_o_n       : out std_logic;
  21             pcl_a_o_n       : out std_logic;
  22             pch_d_i_n       : out std_logic;
  23             pch_d_o_n       : out std_logic;
  24             pch_a_o_n       : out std_logic;
  25             pc_inc_n        : out std_logic;
  26             r_nw            : out std_logic
  27         );
  28 end decoder;
  29
  30 architecture rtl of decoder is
  31
  32 procedure d_print(msg : string) is
  33 variable out_l : line;
  34 begin
  35     write(out_l, msg);
  36     writeline(output, out_l);
  37 end  procedure;
  38
  39 procedure d_print(msg : string; sig : std_logic_vector) is
  40 variable out_l : line;
  41 begin
  42     write(out_l, msg);
  43     write(out_l, sig);
  44     writeline(output, out_l);
  45 end  procedure;
  46
  47 procedure d_print(msg : string; ival : integer) is
  48 variable out_l : line;
  49 begin
  50     write(out_l, msg);
  51     write(out_l, ival);
  52     writeline(output, out_l);
  53 end  procedure;
  54
  55 type dec_status is (reset0, reset1, reset2, reset3, reset4, reset5,
  56                     fetch, exec,
  57                     sei,
  58                     ldx1, ldx2, ldx3,
  59                     jmp1, jmp2, jmp3, jmp4,
  60                     nop,
  61                     unknown_stat
  62                     );
  63
  64 signal cur_status : dec_status;
  65
  66 begin
  67
  68     main_p : process (set_clk, trig_clk, res_n)
  69     begin
  70         if (res_n'event and res_n = '0') then
  71             d_print(string'("reset"));
  72             cur_status <= reset0;
  73         end if;
  74
  75         if (set_clk'event and set_clk = '1') then
  76             d_print(string'("*"));
  77
  78             case cur_status is
  79                 when reset0 =>
  80                     cur_status <= reset1;
  81                 when reset1 =>
  82                     cur_status <= reset2;
  83                 when reset2 =>
  84                     cur_status <= reset3;
  85                 when reset3 =>
  86                     cur_status <= reset4;
  87                 when reset4 =>
  88                     cur_status <= reset5;
  89                 when reset5 =>
  90                     cur_status <= fetch;
  91                 when fetch =>
  92                     d_print(string'("fetch"));
  93                     pcl_a_o_n <= '0';
  94                     pch_a_o_n <= '0';
  95                     r_nw <= '1';
  96                     pc_inc_n <= '0';
  97                     cur_status <= exec;
  98                 when exec =>
  99                     d_print(string'(" exec and decode "), conv_integer(instruction));
 100                     ---one byte instruction decoding.
 101                     if instruction = conv_std_logic_vector(16#78#, dsize) then
 102                         --0x78 = 120
 103                         d_print(string'("   sei"));
 104                         pcl_a_o_n <= '1';
 105                         pch_a_o_n <= '1';
 106                         pc_inc_n <= '1';
 107                         ---set flag operation here.
 108                         cur_status <= fetch;
 109                     elsif instruction = conv_std_logic_vector(16#a2#, dsize) then
 110                         --0xa2 = 162
 111                         d_print(string'("   ldx 0"));
 112                         pcl_a_o_n <= '0';
 113                         pch_a_o_n <= '0';
 114                         pc_inc_n <= '0';
 115                         ---load X operation here.
 116                         cur_status <= fetch;
 117                     elsif instruction = conv_std_logic_vector(16#9a#, dsize) then
 118                         --0x9a = 154
 119                         d_print(string'("   txs"));
 120                         pcl_a_o_n <= '1';
 121                         pch_a_o_n <= '1';
 122                         pc_inc_n <= '1';
 123                         cur_status <= fetch;
 124                     elsif instruction = conv_std_logic_vector(16#4c#, dsize) then
 125                         --0x4c = 76
 126                         cur_status <= jmp1;
 127                         d_print(string'("   jmp 0"));
 128                         pc_inc_n <= '0';
 129                         pcl_a_o_n <= '0';
 130                         pch_a_o_n <= '0';
 131                         cur_status <= jmp1;
 132
 133                     else
 134                         cur_status <= unknown_stat;
 135                         d_print(string'("unknown inst."));
 136                         pc_inc_n <= '1';
 137                         pcl_a_o_n <= '1';
 138                         pch_a_o_n <= '1';
 139                     end if;
 140
 141                 when ldx1 =>
 142                     d_print(string'("   ldx 1"));
 143                     cur_status <= unknown_stat;
 144                 when jmp1 =>
 145                     d_print(string'("   jmp 1"));
 146                     pc_inc_n <= '0';
 147                     pcl_a_o_n <= '1';
 148                     pch_a_o_n <= '1';
 149                     cur_status <= fetch;
 150                 when jmp2 =>
 151                     d_print(string'("   jmp 2"));
 152
 153                 when others => null;
 154                     d_print(string'("unknown status."));
 155                     cur_status <= unknown_stat;
 156             end case;
 157         end if;
 158
 159     end process;
 160
 161 end rtl;
 162