`timescale 1us/1us

module instruction_decode_tb;

logic [15:0] tst_instruction, tst_result;
logic tst_destination_A, tst_destination_D, tst_destination_pA;
logic [15:0] tst_data_A, tst_data_D, tst_data_pA;
logic tst_should_jump;

instruction_decode uut (
  .instruction_in(tst_instruction),
  .dst_A_out(tst_destination_A),
  .dst_D_out(tst_destination_D),
  .dst_pA_out(tst_destination_pA),
  .A_in(tst_data_A),
  .D_in(tst_data_D),
  .pA_in(tst_data_pA),
  .result_out(tst_result),
  .do_jump_out(tst_should_jump)
);

string filename;
initial begin
`ifdef DUMP_FILE_NAME
  filename=`DUMP_FILE_NAME;
`else
  filename="instruction_decode.lxt2";
`endif
  $dumpfile(filename); $dumpvars();
end

`define TB_CHECK(result, expected) assert(result == expected) else $error("Expected %x, got %x", expected, result);

initial begin
  #1

  // LDI 0
  tst_instruction = 0;
  tst_data_A = 0;
  tst_data_D = 0;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 0);
  `TB_CHECK(tst_destination_A, 1);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // LDI ff
  tst_instruction = 'hff;
  tst_data_A = 0;
  tst_data_D = 0;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 'hff);
  `TB_CHECK(tst_destination_A, 1);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // Unless otherwise specified,
  // X=D
  // Y=A

  // (nodest) = D & A
  tst_instruction = 'h8000;
  tst_data_A = 0;
  tst_data_D = 0;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 'h00);
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // A = D & A
  tst_instruction = 'h8020;
  tst_data_A = 0;
  tst_data_D = 0;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 'h0);
  `TB_CHECK(tst_destination_A, 1);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // D = D & A
  tst_instruction = 'h8010;
  tst_data_A = 0;
  tst_data_D = 0;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 'h0);
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 1);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // M = D & A
  tst_instruction = 'h8008;
  tst_data_A = 0;
  tst_data_D = 0;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 'h0);
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 1);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // (result) = D & A
  tst_instruction = 'h8000;
  tst_data_A = 'b1100;
  tst_data_D = 'b1010;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 'b1000);
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // (result) = D | A
  tst_instruction = 'h8100;
  tst_data_A = 'b1100;
  tst_data_D = 'b1010;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 'b1110);
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // (result) = A ^ D
  tst_instruction = 'h8200;
  tst_data_A = 'b1100;
  tst_data_D = 'b1010;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 'b0110);
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // (result) = ~D
  tst_instruction = 'h8300;
  tst_data_A = 'b1010;
  tst_data_D = 'haaaa;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 'h5555);
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // (result) = D + A
  tst_instruction = 'h8400;
  tst_data_A = 2;
  tst_data_D = 3;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 5);
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // (result) = D + 1
  tst_instruction = 'h8500;
  tst_data_A = 5;
  tst_data_D = 7;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 8);
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // (result) = D - A
  tst_instruction = 'h8600;
  tst_data_A = 7;
  tst_data_D = 13;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 6);
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // (result) = D - 1
  tst_instruction = 'h8700;
  tst_data_A = 5;
  tst_data_D = 7;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 6);
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // bit 12: M
  // (result) = D & M
  tst_instruction = 'h9000;
  tst_data_A = 0;
  tst_data_D = 'b1010;
  tst_data_pA = 'b1100;
  #1
  `TB_CHECK(tst_result, 'b1000);
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // bit 7: zx
  // (result) = 0 + A
  tst_instruction = 'h8480;
  tst_data_A = 2;
  tst_data_D = 3;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 2);
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // bit 6: sw
  // (result) = A - D
  tst_instruction = 'h8640;
  tst_data_A = 13;
  tst_data_D = 7;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 6);
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // bit 6+7: sw+zx
  // (result) = 0 - D
  tst_instruction = 'h86c0;
  tst_data_A = 13;
  tst_data_D = 7;
  tst_data_pA = 0;
  #1
  `TB_CHECK(tst_result, 16'(-7));
  `TB_CHECK(tst_destination_A, 0);
  `TB_CHECK(tst_destination_D, 0);
  `TB_CHECK(tst_destination_pA, 0);
  `TB_CHECK(tst_should_jump, 0);
  #1

  // bit2(jl), bit1(je), bit0(jg)

  // --zero
  // (result) = D(0) + A(0), jl
  tst_instruction = 'h8404;
  tst_data_A = 0;
  tst_data_D = 0;
  #1
  `TB_CHECK(tst_should_jump, 0);
  #1

  // (result) = D(0) + A(0), je
  tst_instruction = 'h8402;
  tst_data_A = 0;
  tst_data_D = 0;
  #1
  `TB_CHECK(tst_should_jump, 1);
  #1

  // (result) = D(0) + A(0), jg
  tst_instruction = 'h8401;
  tst_data_A = 0;
  tst_data_D = 0;
  #1
  `TB_CHECK(tst_should_jump, 0);
  #1

  // -- >0
  // (result) = D(0) + A(0), jl
  tst_instruction = 'h8404;
  tst_data_A = 1;
  tst_data_D = 0;
  #1
  `TB_CHECK(tst_should_jump, 0);
  #1

  // (result) = D(0) + A(0), je
  tst_instruction = 'h8402;
  tst_data_A = 1;
  tst_data_D = 0;
  #1
  `TB_CHECK(tst_should_jump, 0);
  #1

  // (result) = D(0) + A(0), jg
  tst_instruction = 'h8401;
  tst_data_A = 1;
  tst_data_D = 0;
  #1
  `TB_CHECK(tst_should_jump, 1);
  #1

  // -- <0
  // (result) = D(0) + A(0), jl
  tst_instruction = 'h8404;
  tst_data_A = -1;
  tst_data_D = 0;
  #1
  `TB_CHECK(tst_should_jump, 1);
  #1

  // (result) = D(0) + A(0), je
  tst_instruction = 'h8402;
  tst_data_A = -1;
  tst_data_D = 0;
  #1
  `TB_CHECK(tst_should_jump, 0);
  #1

  // (result) = D(0) + A(0), jg
  tst_instruction = 'h8401;
  tst_data_A = -1;
  tst_data_D = 0;
  #1
  `TB_CHECK(tst_should_jump, 0);
  #1

  $finish();
end

endmodule