atosm.v

   1 // Atosm Chip
   2 // Copyright (C) 2008 Tomasz Malesinski <tmal@mimuw.edu.pl>
   3 //
   4 // This program is free software; you can redistribute it and/or modify
   5 // it under the terms of the GNU General Public License as published by
   6 // the Free Software Foundation; either version 2 of the License, or
   7 // (at your option) any later version.
   8 //
   9 // This program is distributed in the hope that it will be useful,
  10 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 // GNU General Public License for more details.
  13 //
  14 // You should have received a copy of the GNU General Public License
  15 // along with this program; if not, write to the Free Software
  16 // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  17
  18 `include "atari.v"
  19
  20 module atosm(rst_i, clk_i,
  21              atari_clk_i, atari_clk2_i);
  22    input rst_i, clk_i, atari_clk_i, atari_clk2_i;
  23
  24    wire rst_i, clk_i, atari_clk_i, atari_clk2_i;
  25
  26    wire [15:0] adr;
  27    reg [7:0]  slavedat_o;
  28    wire [7:0] masterdat_o;
  29    wire       stb;
  30    wire       we;
  31    wire       ack;
  32    wire       cyc;
  33
  34    // Masters outputs.
  35    wire [15:0] cpuadr_o;
  36    wire [7:0]  cpudat_o;
  37    wire        cpustb_o;
  38    wire        cpuwe_o;
  39    wire        cpucyc_o;
  40
  41    // Outputs from address decoder.
  42    reg         ramsel, romsel, atarisel;
  43    reg         dummysel;
  44
  45    // Slaves STB_I signals.
  46    wire        ramstb, romstb, ataristb;
  47    wire        dummystb;
  48
  49    // Slaves DAT_O signals.
  50    wire [7:0]  ramdat_o, romdat_o, ataridat_o;
  51
  52    // Slaves ACK_O signals.
  53    wire        ramack_o, romack_o, atariack_o;
  54
  55    // Masters ACK_I signals.
  56    wire        cpuack_i;
  57
  58    wire       nmi, irq;
  59
  60    assign     masterdat_o = cpudat_o;
  61    assign     adr = cpuadr_o;
  62    assign     we = cpuwe_o;
  63    assign     stb = cpustb_o;
  64
  65    assign     cyc = cpucyc_o;
  66
  67    // Address decoder.
  68    always @ (adr) begin
  69       ramsel = 0;
  70       romsel = 0;
  71       atarisel = 0;
  72       dummysel = 0;
  73       if (adr[15] == 0)
  74         ramsel = 1;
  75       else if (adr[15:8] == 8'h80)
  76         atarisel = 1;
  77       else if (adr[15:14] == 2'b11)
  78         romsel = 1;
  79       else
  80         dummysel = 1;
  81    end
  82
  83    // Slaves stb_i.
  84    assign ramstb = ramsel & cyc & stb;
  85    assign romstb = romsel & cyc & stb;
  86    assign ataristb = atarisel & cyc & stb;
  87    assign dummystb = dummysel & cyc & stb;
  88
  89    assign ack = ramack_o | romack_o | atariack_o | dummystb;
  90
  91    assign cpuack_i = ack;
  92
  93    // Slaves dat_o mux.
  94    always @ (ramsel or ramdat_o or
  95              romsel or romdat_o or
  96              atarisel or ataridat_o)
  97      if (ramsel)
  98        slavedat_o = ramdat_o;
  99      else if (romsel)
 100        slavedat_o = romdat_o;
 101      else if (atarisel)
 102        slavedat_o = ataridat_o;
 103      else
 104        slavedat_o = 'hff;
 105
 106    assign nmi = 0;
 107    assign irq = 0;
 108
 109    defparam u_ram.size = 'h8000;
 110    defparam u_ram.adrbits = 15;
 111
 112    ram u_ram(.clk_i(clk_i),
 113              .adr_i(adr[14:0]),
 114              .dat_i(masterdat_o),
 115              .rst_i(rst_i),
 116              .stb_i(ramstb),
 117              .we_i(we),
 118              .ack_o(ramack_o),
 119              .dat_o(ramdat_o));
 120
 121    defparam u_rom.size = 'h4000;
 122    defparam u_rom.adrbits = 14;
 123
 124    rom u_rom(.clk_i(clk_i),
 125              .adr_i(adr[13:0]),
 126              .rst_i(rst_i),
 127              .stb_i(romstb),
 128              .ack_o(romack_o),
 129              .dat_o(romdat_o));
 130
 131    cpu6502 u_cpu(.clk_i(clk_i),
 132                  .adr_o(cpuadr_o),
 133                  .dat_i(slavedat_o),
 134                  .rst_i(rst_i),
 135                  .stb_o(cpustb_o),
 136                  .we_o(cpuwe_o),
 137                  .ack_i(cpuack_i),
 138                  .dat_o(cpudat_o),
 139                  .cyc_o(cpucyc_o),
 140                  .nmi(nmi),
 141                  .irq(irq));
 142
 143    atari u_atari(.clk_i(atari_clk_i),
 144                  .clk2_i(atari_clk2_i),
 145                  .rst_i(rst_i),
 146                  .ext_rst_i(rst_i),
 147                  .ext_clk_i(clk_i),
 148                  .ext_adr_i(adr[3:0]),
 149                  .ext_dat_i(masterdat_o),
 150                  .ext_dat_o(ataridat_o),
 151                  .ext_we_i(we),
 152                  .ext_stb_i(ataristb),
 153                  .ext_ack_o(atariack_o));
 154
 155 endmodule