Snippets

T McDonnell A Simple Computer

Created by T McDonnell
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Program ASC (Input,Output); {A Simple Computer}

uses CRT, DOS;

{----------------(ASC Simulation)---------------}
{CPU Registers}
var
  ACC : Longint; {ACCumulator}
  MBR : Longint; {Memory Buffer Register}
  MAR : Word;    {Memory Address Register}
  IR : Word;     {Instruction Register}
  PC : Word;     {Program Counter}
  IR1 : Word;    {Index Register 1}
  IR2 : Word;    {Index Register 2}
  IR3 : Word;    {Index Register 3}

{Random Access Memory}
  RAM : Array[1..1000] of Longint; {1Kb RAM}
{IR decoder variables}
  memoryAddr : Integer;   {IR bits 7-15} {0-511}
  idx : Integer;          {IR bits 0-1}  {0-3}
  indirect : Integer;     {IT bit 2}     {0-1}
  opcode : Integer;       {IR bits 3-6}  {0-15}
{-----------------------------------------------}


{-----------------------------------------------}
var key : Char;  {Stores users menu choice}
{-----------------------------------------------}


{-----------------------------------------------}
procedure PrintHex( X : Word);
  const s : array[0..15] of char = '0123456789ABCDEF';
  var i : integer;

  begin
    for i:=3 downto 0 do
      Write( s[$000F and (X shr(i*4))]);
  end;
  {taken from PASCAL Programers Phasebook}
  {by Ian A. Clari, Sigma Press, 1992}
{-----------------------------------------------}


procedure RegWin;
  begin
    Window(1,1,80,8);
    TextBackground(blue);
    TextColor(white);
    ClrScr;
    WriteLn('+============================================================================+');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    Write('+============================================================================+');
    TextColor(yellow);
    GotoXY(9,3); Write('ACCumalator:');             GotoXY(44,3); Write('Instruction Register:');
    GotoXY(9,4); Write('Program Counter:');         GotoXY(44,4); Write('Index Register 1:');
    GotoXY(9,5); Write('Memory Buffer Register:');  GotoXY(44,5); Write('Index Register 2:');
    GotoXY(9,6); Write('Memory Address Register:'); GotoXY(44,6); Write('Index Register 3:');
    TextColor(white);
    GotoXY(34,3); PrintHex(ACC); GotoXY(66,3); PrintHex(IR);
    GotoXY(34,4); PrintHex(PC);  GotoXY(66,4); PrintHex(IR1);
    GotoXY(34,5); PrintHex(MBR); GotoXY(66,5); PrintHex(IR2);
    GotoXY(34,6); PrintHex(MAR); GotoXY(66,6); PrintHex(IR3);
  end;


procedure MainWin;
  begin
    Window(1,9,80,25);
    TextBackground(blue);
    TextColor(white);
    ClrScr;
    WriteLn('+============================================================================+');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    Write('+============================================================================+');
    TextColor(lightred);
    GotoXY(11,16);
    Write('A Simple Computer simulator - T.McDonnell, SYS-1C22,UEA,1999');
    TextColor(yellow);
    GotoXY(17,3); Write('1.....Load progam to ASC RAM');
    GotoXY(17,4); Write('2.....Start ASC simulation using program in ASC RAM');
    GotoXY(17,5); Write('3.....Step through a running ASC Simulation');
    GotoXY(17,6); Write('4.....Show map of ASC RAM');
    GotoXY(17,7); Write('5.....Edit contents of a ASC CPU register');
    GotoXY(17,8); Write('6.....Edit contents of a ASC RAM address');
    GotoXY(17,9); Write('7.....Set program break points');
    GotoXY(17,11); Write('C.....Clear registers');
    GotoXY(17,13); Write('X.....Exit ASC simulator');
  end;


procedure Dialog;
  begin
    Window(21,12,60,18);
    TextBackground(cyan);
    TextColor(white);
    WriteLn('+======================================+');
    WriteLn('|                                      |');
    WriteLn('|                                      |');
    WriteLn('|                                      |');
    WriteLn('|                                      |');
    WriteLn('|                                      |');
    Write('+======================================+');
    TextColor(black);
  end;


procedure Greeting;
  begin
    GotoXY(10,2); Write('A Simple Computer');
    GotoXY(9,6); Write('T. McDonnell, 1999');
    TextColor(lightred+blink);
    GotoXY(10,4); Write('S I M U L A T O R');
    repeat until KeyPressed;
  end;


function Addr : Word;
  var address : Word;

  begin
    CursorOn;
    Dialog; GotoXY(6,4); Write('Address: ');
    GotoXY(6,2); Write('Enter in either Hex or Dec');
    GotoXY(6,6); Write('Use $ for Hex values');
    GotoXY(15,4); TextBackground(lightgray); Write('          ');
    GotoXY(15,4); TextColor(white); ReadLn(address);
    CursorOff;
    MainWin;
    Addr := address;
  end;


function Val : Word;
  var value : Word;

  begin
    CursorOn;
    Dialog; GotoXY(6,4); Write('Value: ');
    GotoXY(6,2); Write('Enter in either Hex or Dec');
    GotoXY(6,6); Write('Use $ for Hex values');
    GotoXY(15,4); TextBackground(lightgray); Write('          ');
    GotoXY(15,4); TextColor(white); ReadLn(value);
    CursorOff;
    MainWin;
    Val := value;
  end;


function UserIn : Word;
  var data : Word;

  begin
    Window(21,1,60,7);
    TextBackground(cyan);
    TextColor(white);
    WriteLn('+---------------------------------------------------------+');
    WriteLn('|                                                         |');
    WriteLn('|                                                         |');
    WriteLn('|                                                         |');
    WriteLn('|                                                         |');
    WriteLn('|                                                         |');
    Write('+---------------------------------------------------------+');
    TextColor(black);
    Window(22,2,69,6);
    GotoXY(3,3); Write('Enter Data: ');
    TextBackground(lightgray); TextColor(white);
    Write('               '); GotoXY(15,3);
    ReadLn(data);
    UserIn := data;
  end;


procedure UserOut(data:Word);
  begin
    Window(21,1,60,7);
    TextBackground(cyan);
    TextColor(white);
    WriteLn('+---------------------------------------------------------+');
    WriteLn('|                                                         |');
    WriteLn('|                                                         |');
    WriteLn('|                                                         |');
    WriteLn('|                                                         |');
    WriteLn('|                                                         |');
    Write('+---------------------------------------------------------+');
    TextColor(black);
    Window(22,2,69,6);
    WriteLn(data);
  end;


procedure Fetch;
  begin
    memoryAddr := 0; idx := 0; indirect := 0; opcode := 0;
    MAR := PC;
    MBR := RAM[MAR];
    PC := PC + 1;
    IR := MBR;
  end;


procedure Decode;
  begin
    memoryAddr := IR;

    {--------------------------------------}
    {calculate which index register, if any, is used}
    if memoryAddr >= $0000 then
    begin
      idx := 3;
      memoryAddr := memoryAddr - $0000;
    end
    else if memoryAddr >=$8000 then
    begin
      idx := 2;
      memoryAddr := memoryAddr - $8000;
    end
    else if memoryAddr >=$4000 then
    begin
      idx := 1;
      memoryAddr := memoryAddr - $8000;
    end;

    {--------------------------------------}
    {check for indirect addressing mode}
    if memoryAddr >= $2000 then
    begin
      indirect := 1;
      memoryAddr := memoryAddr - $2000;
    end;

    {--------------------------------------}
    {remove opcode}
    if memoryAddr >= $1E00 then
    begin
      opcode := $F;           {TDX I,x}
      memoryAddr := memoryAddr - $1E00;
    end
    else if memoryAddr >= $1C00 then
    begin
      opcode := $E;           {TIX I,x}
      memoryAddr := memoryAddr - $1C00;
    end
    else if memoryAddr >= $1A00 then
    begin
      opcode := $D;           {STX I,x}
      memoryAddr := memoryAddr - $1A00;
    end
    else if memoryAddr >= $1800 then
    begin
      opcode := $C;           {LDX, I,x}
      memoryAddr := memoryAddr - $1800;
    end
    else if memoryAddr >= $1600 then
    begin
      opcode := $B;           {SHR}
      memoryAddr := memoryAddr - $1600;
    end
    else if memoryAddr >= $1400 then
    begin
      opcode := $A;           {SHL}
      memoryAddr := memoryAddr - $1400;
    end
    else if memoryAddr >= $1200 then
    begin
      opcode := $9;           {WWD}
      memoryAddr := memoryAddr - $1200;
    end
    else if memoryAddr >= $1000 then
    begin
      opcode := $8;           {RWD}
      memoryAddr := memoryAddr - $1000;
    end
    else if memoryAddr >= $0E00 then
    begin
      opcode := $7;           {BIN x}
      memoryAddr := memoryAddr - $0E00;
    end
    else if memoryAddr >= $0C00 then
    begin
      opcode := $6;           {BIP x}
      memoryAddr := memoryAddr - $0C00;
    end
    else if memoryAddr >= $0A00 then
    begin
      opcode := $5;           {BRU x}
      memoryAddr := memoryAddr - $0A00;
    end
    else if memoryAddr >= $0800 then
    begin
      opcode := $4;           {HLT}
      memoryAddr := memoryAddr - $0800;
    end
    else if memoryAddr >= $0600 then
    begin
      opcode := $3;           {TCA}
      memoryAddr := memoryAddr - $0600;
    end
    else if memoryAddr >= $0400 then
    begin
      opcode := $2;           {ADD x}
      memoryAddr := memoryAddr - $0400;
    end
    else if memoryAddr >= $0200 then
    begin
      opcode := $1;           {STA x}
      memoryAddr := memoryAddr - $0200;
    end
    else if memoryAddr >= $0000 then
    begin
      opcode := $0;           {LDA x}
      memoryAddr := memoryAddr - $0000;
    end;
    {------------------------------}
    {update registers}
    MAR := memoryAddr;

    if idx = 0 then
      begin
        if indirect = 0 then
          begin
            MBR := RAM[MAR];
          end
          else
          begin
            MBR := RAM[MAR];
            MAR := MBR;
            MBR := RAM[MAR];
          end;
      end
      else
      begin
        if indirect = 0 then
        begin
          if idx = 1 then MBR := RAM[MAR + IR1];
          if idx = 2 then MBR := RAM[MAR + IR2];
          if idx = 3 then MBR := RAM[MAR + IR3];
        end
        else
        begin
          if idx = 1 then MBR := RAM[MAR + IR1];
          if idx = 2 then MBR := RAM[MAR + IR2];
          if idx = 3 then MBR := RAM[MAR + IR3];
          MAR := MBR;
          MBR := RAM[MAR];
        end;
      end;

    if opcode = $C then
      begin
        MAR := memoryAddr;
        MBR := RAM[MAR];
      end;

    if opcode = $D then MAR := memoryAddr;
    if opcode = $E then MAR := memoryAddr;
    if opcode = $F then MAR := memoryAddr;
  end;


procedure Execute;
  begin
    if opcode = $0 then ACC := MBR;
    if opcode = $1 then
      begin
        MBR := ACC;
        RAM[MAR] := MBR;
      end;
    if opcode = $2 then ACC := ACC + MBR;
    if opcode = $3 then ACC := 0 - ACC;
    if opcode = $5 then PC := MAR;
    if opcode = $6 then if ACC > 0 then PC := MAR;
    if opcode = $7 then if ACC < 0 then PC := MAR;
    if opcode = $8 then ACC := UserIn;
    if opcode = $9 then UserOut(ACC);
    if opcode = $A then ACC := ACC * 2;
    if opcode = $B then ACC := ACC DIV 2;
    if opcode = $C then
      begin
        if idx = 1 then IR1 := MBR;
        if idx = 2 then IR2 := MBR;
        if idx = 3 then IR3 := MBR;
      end;
    if opcode = $D then
      begin
        if idx = 1 then MBR := IR1;
        if idx = 2 then MBR := IR2;
        if idx = 3 then MBR := IR3;
      end;
    if opcode = $E then
      begin
        if idx = 1 then
          begin
            IR1 := IR1 + 1;
            if IR1 = 0 then PC := MAR;
          end;
        if idx = 2 then
          begin
            IR2 := IR2 + 1;
            if IR2 = 0 then PC := MAR;
          end;
        if idx = 3 then
          begin
            IR3 := IR3 + 1;
            if IR3 = 0 then PC := MAR;
          end;
      end;
    if opcode = $F then
      begin
        if idx = 1 then
          begin
            IR1 := IR1 - 1;
            if not(IR1 = 0) then PC := MAR;
          end;
        if idx = 2 then
          begin
            IR2 := IR2 - 1;
            if not(IR2 = 0) then PC := MAR;
          end;
        if idx = 3 then
          begin
            IR3 := IR3 - 1;
            if not(IR3 = 0) then PC := MAR;
          end;
      end;
  end;

  {---------------------------------------}
procedure Load;
  var F : Text;
      userfile : String;
      address : integer;
      temp : Word;
      SRec : SearchRec;

  begin
    {--------------------}
    Dialog;
    GotoXY(3,2); Write('Load ASC machine code from...');
    GotoXY(3,5); Write('Do not enter DOS extension (.asc)');
    GotoXY(5,4); Write('File: ');
    Textbackground(lightgray); TextColor(white); Write('          ');
    CursorOn;
    repeat
      GotoXY(11,4); ReadLn(userfile);
    until not(userfile='');
    userfile := userfile + '.asc';
    CursorOff; Dialog;
    TextColor(lightred+blink); GotoXY(11,4); Write('Processing ',userfile);
    {--------------------}
    FindFirst(userfile, AnyFile, SRec);
    if DosError = 2 then
      begin
        Dialog; GotoXY(6,4); TextColor(lightred);
        Write('ERROR - File does not exist');
        repeat until KeyPressed;
      end
      else
      begin
        {---------------------}
        address := Addr;
        Dialog;
        TextColor(lightred+blink);
        GotoXY(11,4); Write('Processing ',userfile);
        {---------------------}
        Assign(f,userfile); Reset(f);
        repeat
          if address > 1000 then
            begin
              Read(F, temp);
              Dialog; GotoXY(6,4); TextColor(lightred);
              Write('FATAL ERROR - ASC out of RAM');
              repeat until KeyPressed;
            end
            else
            begin
              Read(F, RAM[address]);
              address := address + 1;
            end;
        until Eof(F);
        close(F);
      end;
    MainWin;
  end;


procedure FetchExecute;
  begin
    PC := Addr;
    Dialog; TextColor(lightred+blink);
    GotoXY(11,4); Write('Processing...');
    repeat
      Fetch;
      Decode;
      Execute;
      RegWin;
    until opcode = $4;
    MainWin;
  end;


procedure Trace;
  var
    step : char;
    charcheck : Integer;

  begin
    PC := Addr;
    Dialog;
    GotoXY(6,3); Write('[S] - Step');
    GotoXY(6,5); Write('[X] - Exit');
    repeat
      charcheck := 0;
      Fetch;
      Decode;
      Execute;
      RegWin;
      repeat
        repeat until KeyPressed;
        step := ReadKey;
        if step = 'x' then
        begin
          step := 'X';
          charcheck := 1;
        end;
        if step = 'X' then charcheck := 1;
        if step = 's' then charcheck := 1;
        if step = 'S' then charcheck := 1;
      until charcheck = 1;
      if opcode = $4 then step := 'X';
    until step = 'X';
    MainWin;
  end;


procedure Map;
  var
    startAddr : Word;
    endAddr : Word;
    address : Word;

  begin
    Dialog; GotoXY(6,3); Write('Start Addr: ');
    GotoXY(6,5); Write('End Addr: ');
    GotoXY(6,2); Write('Enter in either Hex or Dec');
    GotoXY(6,6); Write('Use $ for Hex values');
    TextBackground(lightgray);
    GotoXY(18,3); Write('          ');
    GotoXY(18,5); Write('          ');
    CursorOn; TextColor(white);
    GotoXY(18,3); ReadLn(startAddr);
    GotoXY(18,5); ReadLn(endAddr);
    CursorOff;
    MainWin;
    {---------------------------}
    Window(38,1,79,24);
    WriteLn('+----------------------------------------------------------------------------+');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    WriteLn('|                                                                            |');
    Write('+----------------------------------------------------------------------------+');
    TextColor(black);
    GotoXY(4,2); Write('Address      Contents');
    GotoXY(19,3); Write('Hex      Decimal');
    {-------------------------------}
    Window(43,5,74,22);
    for address := startAddr to endAddr do
      begin
        TextColor(yellow); PrintHex(address);
        TextColor(white); Write('      '); PrintHex(RAM[address]);
        WriteLn('      ',RAM[address]);
      end;
    repeat until KeyPressed;
    RegWin; MainWin;
  end;


procedure RegEdit;
  var
    reg : String;

  begin
    Dialog;
    GotoXY(3,2); Write('Enter Register code');
    GotoXY(3,6); Write('Capital letters in register window');
    GotoXY(6,4); Write('Register: ');
    TextBackground(lightgray); TextColor(white);
    GotoXY(16,4); Write('          ');
    GotoXY(16,4); ReadLn(reg);
    if reg='ACC' then ACC := Val;
    if reg='acc' then ACC := Val;
    if reg='PC' then PC := Val;
    if reg='pc' then PC := Val;
    if reg='MBR' then MBR := Val;
    if reg='mbr' then MBR := Val;
    if reg='MAR' then MAR := Val;
    if reg='mar' then MAR := Val;
    if reg='IR' then IR := Val;
    if reg='ir' then IR := Val;
    if reg='IR1' then IR1 := Val;
    if reg='ir1' then IR1 := Val;
    if reg='IR2' then IR2 := Val;
    if reg='ir2' then IR2 := Val;
    if reg='IR3' then IR3 := Val;
    if reg='ir3' then IR3 := Val;
    RegWin;
    MainWin;
  end;


procedure AddrEdit;
  var
    address : Word;

  begin
    address := Addr;
    RAM[address] := Val;
  end;


procedure BreakPts;
  begin
  end;


procedure Clear;
  begin
    ACC := 0;  IR := 0;
    PC := 0;   IR1 := 0;
    MAR := 0;  IR2 := 0;
    MBR := 0;  IR3 := 0;
    RegWin;
  end;

{-------------------------------------------------}

{Main Subroutine}
begin
  {startup}
  CursorOff;
  RegWin;
  MainWin;
  Dialog;
  Greeting;
  MainWin;

  {main loop}
  repeat
    key := ReadKey;
    case key of
      '1' : Load;
      '2' : FetchExecute;
      '3' : Trace;
      '4' : Map;
      '5' : RegEdit;
      '6' : AddrEdit;
      '7' : BreakPts;
      'C' : Clear;
      'c' : Clear;
      'x' : key := 'X';
    end;
  until key = 'X';
end

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